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DEVELOPMENT OF A SOIL MOISTURE MODEL FOR USE WITH PASSIVE MICROWAVE REMOTE SENSORS

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18 B E D F O R D ROW, LO N D O N W C1R 4 E J , E N G L A N D
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8023014
BAUSCH, WALTER CHARLES
DEVELOPMENT OF A SOIL MOISTURE MODEL FOR USE WITH PASSIVE MICROWAVE
REMOTE SENSORS
Texas A§M University
University
Microfilms
International
300 N. Zeeb Road, Ann Arbor, MI 48106
PH.D.
1980
18 Bedford Row, London WC1R 4EJ, England
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DEVELOPMENT OF A SOIL MOISTURE MODEL FOR USE
WITH PASSIVE MICROWAVE REMOTE SENSORS
A Dissertation
by
WALTER CHARLES BAUSCH
Submitted to the Graduate College of
Texas A&M University
in p a r t i a l f u l f i l l m e n t of the requirement f o r the degree of
DOCTOR OF PHILOSOPHY
May 1980
Major Subject:
A g r ic u lt u r a l Engineering
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DEVELOPMENT OF A SOIL MOISTURE MODEL FOR USE
WITH PASSIVE MICROWAVE REMOTE SENSORS
A Dissertation
by
WALTER CHARLES BAUSCH
Approved as to s t y l e and c on te nt by:
(Chairm&i o f Committee)
(Member)
(Member
(Member)
Member)
(Head o f Department)
May 1980
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ABSTRACT
Development o f a Soil Moisture Model f o r Use with
Passive Microwave Remote Sensors.
(May 1980)
Walter Charles Bausch
B .S ., Texas A&M U n iv er s it y ;
M.S., Texas A&M Univer sit y
Chairman o f Advisory Committee:
Dr. Bruce 0. Blanchard
Soil moisture p r o f i l e s were simulated f o r a hypothetical loam­
l i k e s oi l with a water and heat balance model.
Expected X-band and
L-band radiometer response t o th e se c o n d it io ns were simulated by a
r a d i a t i v e t r a n s f e r model.
From t h e s e s im u l a ti o n s, a model was developed
to estim ate s o il water content in two la ye r s o f a 1.5 m s oi l p r o f i l e .
Soil water cont ent in th e top 21 cm of th e hypothetical s o i l was
r e l a t e d to L-band e m i s s i v i t y over a wide range o f s oi l moisture con di­
tions.
Inverted s o il moisture p r o f i l e s which r e s u l t from small r a in s
were c l a s s i f i e d by use of the r a t e of change in L-band e m i s s i v i t y one
day a f t e r th e r a i n .
The amount of water added to th e s o il p r o f i l e
below the 21 cm depth due t o p e r c o l a ti o n was r e l a t e d to a r a t i o of the
r a t e of change in X-band and L-band e m i s s i v i t i e s one day a f t e r the
rain.
These r e l a t i o n s h i p s were combined i n t o a comprehensive model
t h a t p r e d i c t s so il moisture in two zones of th e s o il p r o f i l e .
This model was t e s t e d with measurements of s o il water co n te n t and
s o il temperature c o l l e c t e d during the f o u r seasons o f th e y e a r in a
sandy loam s o i l contained in an a r r a y of l y s im e te r s .
X-band and L-band
e m i s s i v i t i e s require d in the p r e d i c t o r equations were c a l c u l a t e d by the
with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
iv
r a d i a t i v e t r a n s f e r model from measured s o il moisture and so il tempera­
ture data.
The technique developed from simulated r e s u l t s to c l a s s i f y
in v e rte d s o il moisture p r o f i l e s was found t o be seas on ally dependent.
I t was al so found t h a t the second la y er algorithm showed seasonal
dependence.
P r ed ic ti on s o f s o il water content in th e top 21 cm of th e so il
p r o f i l e from L-band em is si v it y c a l c u l a t e d by t h e r a d i a t i v e t r a n s f e r
model o c c a s i o n a ll y conformed with measured s o i l water content.
Since
the equation to esti mat e s o i l water c o nt en t f o r in ve rte d so il moisture
p r o f i l e s did no t f i t th e measured d a t a , so il water cont ent on such
occurrences was ov erp red ic ted .
Applications o f small amounts o f water
produced th e most disagreement between p r e d ic te d and measured s o il
water cont ent .
An equation t o p r e d i c t s o i l water cont ent in th e top 21 cm of the
s o i l p r o f i l e was developed from an empirical approach t o estimate
e m is s i v it y .
P r ed ic ti o ns of so il water con tent with t h i s equation from
L-band e m is s i v it y estimated by th e empirical technique compared very
well with measured s o il water content re g a r d l e s s o f inv erted soil
moisture p r o f i l e s or amount of applied water.
However, th e r e l a t i o n ­
ship between amount of water added to th e 21 to 150 cm s o i l l a y e r
versus th e r a t i o of th e r a t e of change in X-band and L-band e m i s s i v i t i e s
estimated by the empirical approach s t i l l produced considerable data
scatter.
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V
DEDICATION
This d i s s e r t a t i o n is dedicated to my wi fe, Linda, f o r her
pat ien ce and moral support given to me during th e se p a s t f i v e yea rs .
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vi
ACKNOWLEDGEMENTS
The author would l i k e to acknowledge and thank Dr. Bruce J.
Blanchard f o r his a s s i s t a n c e and guidance throughout the course of
t h i s study.
Appreciation is extended to Dr. E. A. H i l e r , Dr. Donald
L. Reddell, Dr. Charles W. Wendt, and Dr. John L. Nieber f o r t h e i r
encouragement and help ful sugge sti ons .
The author would al so l i k e to
acknowledge Dr. Terry A. Howell and Dr. C. H. M. van Bavel f o r t h e i r
suggestions on the c a l i b r a t i o n of the two-probe de n s it y gauge.
Sincere thanks are extended to Mr. Steve Shiner and Mr. J e f f
Hermes in a s s i s t i n g with data c o l l e c t i o n and data red uc ti o n .
Special
thanks are expressed to Mr. Chris Breedlove in a s s i s t i n g with the
computer graph ic s.
Sincere thanks a r e al so expressed to Mrs. Linda
Stewart f o r typing t h i s d i s s e r t a t i o n .
The author i s indebted to the A g r ic ul t ur al Engineering Department
(Dr. E. A. H i l e r , Head) fo r use o f th e ly sim ete r i n s t a l l a t i o n and use
o f the meteorological equipment.
This study was supported by the
National Science Foundation under p r o j e c t RF-3757 and in p a r t by the
National Oceanic and Atmospheric Administration-National Environmental
S a t e l l i t e Service ( p r o j e c t RF-3843).
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vi i
TABLE OF CONTENTS
Page
ABSTRACT............................................................................................................
iii
DEDICATION .......................................................................................................
v
ACKNOWLEDGEMENTS ..........................................................................................
vi
TABLE OF CONTENTS ........................................................................................
v ii
LIST OF TABLES ...............................................................................................
ix
LIST OF FIGURES .............................................................................................
x
CHAPTER
I
II
III
IV
INTRODUCTION .....................................................................................
1
Objective ................................................................................
Approach ..................................................................................
3
3
REVIEW OF LITERATURE ....................................................................
5
Conventional Soil Moisture Models ............................
Remote Sensing of Soil Moisture ................................
5
10
THEORETICAL DEVELOPMENT OF THE MODEL .................................
16
Procedure ................................................................................
Resu lts ....................................................................................
The Model ................................................................................
16
25
83
EXPERIMENTAL STUDY ........................................................................
89
D es cri pt io n o f Experimental S i t e ..............................
Methods ....................................................................................
Two-Probe Density Gauge C a l ib r a ti o n .............
Measurement Procedures .........................................
Observations from Measured Data .................................
89
90
91
95
98
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viii
TABLE OF CONTENTS (continued)
CHAPTER
Page
V
Ill
VI
DISCUSSION OF RESULTS ..................................................................
V e r i f i c a t i o n o f th e Model .............................................
F i r s t Layer Algorithm ...........................................
Second Layer Algorithm .........................................
Empirical Approach to Estimating Emissivity ___
Ill
Ill
130
142
SUMMARY AND CONCLUSIONS .............................................................
153
Summary ....................................................................................
Conclusions ...........................................................................
Recommendations ...................................................................
153
156
157
REFERENCES ..............................................................................................................
159
VITA ...........................................................................................................................
164
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ix
LIST OF TABLES
TABLE
Page
1
GEOMETRY OF SIMULATED SOIL SYSTEM ..........................................
20
2
SIMULATION PERIOD AMD ASSOCIATED RAINFALL EVENTS ..........
22
3
CONDITIONS THAT EXISTED ON THE DAY OF RAIN FOR THE
SIMULATED RAINFALL EVENTS .................................................................
65
AMOUNT OF WATER (cm) APPLIED TO THE LYSIMETERS
DURING EACH SEASONAL EXPERIMENT ....................................................
96
4
5
6
7
8
9
10
ACTUAL AMOUNT OF WATER APPLIED TO THE SOIL IN
EACH LYSIMETER DURING THE SEASONAL EXPERIMENTS.................
106
AMOUNT OF WATER ADDED (in cm) TO THE 21 TO 150 CM
SOIL LAYER FROM WATER APPLIED (in cm) TO EACH
LYSIMETER DURING THE FOUR SEASONAL EXPERIMENTS ...................
136
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS
OF WATER ADDED ( i n cm) TO THE 21 TO 150 CM
SOIL LAYER DURING THE SPRING EXPERIMENT ..................................
137
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS
OF WATER ADDED ( in cm) TO THE 21 TO 150 CM
SOIL LAYER DURINGTHE SUMMER EXPERIMENT ..............................
138
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS
OF WATER ADDED (in cm) TO THE 21 TO 150 CM
SOIL LAYER DURINGTHE FALL EXPERIMENT ..................................
139
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS
OF WATER ADDED (in cm) TO THE 21 TO 150 CM
SOIL LAYER DURINGTHE WINTER EXPERIMENT ..............................
140
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LIST OF FIGURES
FIGURE
1
2
3
4
5
6
Page
R el ati ons hi p between s o il pres su re p o t e n t i a l and
volumetric moisture con tent (Clapp and Hornberger,
1978) f o r the hypothetical loam-like s o i l .
Hydraulic c o nd uc ti vi ty versus volumetric moisture
c o nt en t was c a l c u l a t e d a f t e r Jackson (1972)...................
18
Simulated s o i l moisture p r o f i l e s produced by 1.27
cm p r e c i p i t a t i o n on a hypothetical loam-like s o il
t h a t had pre viously received a 2.54 cm r a i n .
J u l i a n day 232 re pr es en ts the s o i l moisture
s t a t u s p r i o r to the r a i n f a l l e v e n t .......................................
25
Simulated s o il moisture p r o f i l e s produced by 2.54
cm p r e c i p i t a t i o n on a hypothetical loam-like so il
t h a t was i n i t i a l l y dry. J u l i a n day 202 r e p r e s e n t s
the s o i l moisture s t a t u s p r i o r to the r a i n f a l l
e v e n t .....................................................................................................
27
Simulated s o il moisture p r o f i l e s produced by 2.54
cm p r e c i p i t a t i o n on a hy po thetical loam-like s o il
t h a t had pr ev iou sl y received a 2.54 cm r a i n .
J u l i a n day 212 r e p r e s e n t s the s o i l moisture
s t a t u s p r i o r to the r a i n f a l l e v e n t ........................................
28
Simulated s o i l moisture p r o f i l e s produced by 5.08
cm p r e c i p i t a t i o n on a hypothetical loam-like so il
t h a t was i n i t i a l l y dry. J u l i a n day 196 r e p r e s e n t s
the s o i l moisture s t a t u s p r i o r to the r a i n f a l l
e v e n t .....................................................................................................
29
Simulated s o i l moisture p r o f i l e s produced by 5.08
cm p r e c i p i t a t i o n on a h ypo the tic al loa m-like s o il
t h a t had pre viously received a 5.08 cm r a i n .
J u l i a n day 212 r e p r e s e n t s the s o i l moisture
s t a t u s p r i o r to the r a i n f a l l e v e n t ........................................
30
Simulated s o i l moisture p r o f i l e s produced by 7.52
cm p r e c i p i t a t i o n on a hypoth et ica l loam-like so il
t h a t was i n i t i a l l y dry. J u l i a n day 196 r e p re s e n t s
the s o i l moisture s t a t u s p r i o r t o th e r a i n f a l l
e v e n t .....................................................................................................
31
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LIST OF FIGURES (continued)
FIGURE
8
9
10
11
12
13
14
Page
Simulated s o il moisture p r o f i l e s produced by 7.62
cm p r e c i p i t a t i o n on a hypothetical loam-like s o i l
t h a t had pr evi ou sl y received a 7.62 cm r a i n .
J u l i a n day 212 re p r e s e n t s the s o il moisture
s t a t u s p r i o r to the r a i n f a l l e v e n t .......................................
32
Simulated s o i l moisture p r o f i l e s produced by 10.16
cm p r e c i p i t a t i o n on a hypothetical loam-like s o il
t h a t was i n i t i a l l y dry. J u l i a n day 196 r e p r e s e n t s
the s o i l moisture s t a t u s p r i o r to the r a i n f a l l
e v e n t .....................................................................................................
33
Simulated s o i l moisture p r o f i l e s produced by 10.16
cm p r e c i p i t a t i o n on a hypothetical loa m-like s o il
t h a t had pr evi ous ly received a 5.08 cm r a i n .
J u l i a n day 212 r e p r e s e n t s the s o il moisture
s t a t u s p r i o r to the r a i n f a l l e v e n t .......................................
34
Con tri bu tio n of emitted microwave energy with depth
in r e l a t i o n to the t o t a l emitted energy as
c a l c u l a t e d by the r a d i a t i v e t r a n s f e r model f o r Xband (A) and L-band ( 8 ) from 1.27 cm p r e c i p i t a t i o n
on a hy po the tica l loam-like s o i l t h a t had
p r ev io u s l y received a 2.54 cm r a i n .......................................
36
Con tribu tion of emitted microwave energy with depth
in r e l a t i o n to the t o t a l emitted energy as
c a l c u l a t e d by the r a d i a t i v e t r a n s f e r model f o r Xband (A) and L-band (B) from 2.54 cm p r e c i p i t a t i o n
on a hy poth etica l loam-like s o i l t h a t had
p re v io us ly received a 2.54 cm r a i n .......................................
37
Con tribu tion of emitted microwave energy with depth
in r e l a t i o n to the t o t a l emitted energy as
c a l c u l a t e d by the r a d i a t i v e t r a n s f e r model f o r Xband (A) and L-band (B) from 5.08 cm p r e c i p i t a t i o n
on a hyp ot h e tic a l loam-like s o i l t h a t had
pr ev io u s l y rece ived a 5.08 cm r a i n .......................................
38
Con tri b ut io n o f emitted microwave energy with depth
in r e l a t i o n t o the t o t a l emitted energy as
c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model f o r Xband (A) and L-band (B) from 7.62 cm p r e c i p i t a t i o n
on a hyp ot h e tic a l loam-like s o il t h a t had
pr evi ous ly rece ive d a 7.62 cm r a i n .......................................
39
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LIST OF FIGURES (continued)
FIGURE
15
16
17
18
19
20
21
22
Page
P en et ra tio n depths c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r X-band ( s h o r t dashes) and Lband (long dashes) from simulated s o i l moisture
p r o f i l e s produced by a 2.54 cm r a i n on a hypo­
t h e t i c a l loam-like s o il t h a t had pr ev io us ly
rece ived 2.54 cm p r e c i p i t a t i o n ........................................... .
41
P e n e t ra ti o n depths c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r X-band ( s h o r t dashes) and Lband (long dashes) from simulated s o i l moisture
p r o f i l e s produced by a 5.08 cm r a i n on a hypo­
t h e t i c a l loam-like s o i l t h a t had p r ev io us ly
r ec ei ved 5.08 cm p r e c i p i t a t i o n ........................................... .
42
P e n tr a t io n depths c a l c u l a t e d by th e r a d i a t i v e
t r a n s f e r model f o r X-band ( s h o r t dashes) and Lband (long dashes) from simulated s o i l moisture
p r o f i l e s produced by a 7.62 cm r a i n on a hypo­
t h e t i c a l loam-like s o il t h a t p re v io u s ly
received 7.62 cm p r e c i p i t a t i o n ...........................................
43
Pe n tr at io n depths c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r X-band ( s h o r t dashes) and Lband (long dashes) from simulated s o i l moisture
p r o f i l e s produced by a 10.16 cm r a i n on a hypo­
t h e t i c a l loam-like s o il t h a t was i n i t i a l l y d r y .........
44
P en et ra ti o n depths c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r X-band ( s h o r t dashes) and Lband (long dashes) from simulated s o i l moisture
p r o f i l e s produced by a 10.16 cm r a i n on a hypo­
t h e t i c a l loam-like s o i l t h a t had pr ev iou sl y
received 5.08 cm p r e c i p i t a t i o n ...........................................
45
Rel ati on between L-band EQSM and s o i l water content
in the top 15 cm of the hy p o th e ti ca l loam-like
s o i l p r o f i l e ..................................................................................
47
Rel ati on between L-band EQSM and s o i l water con tent
in th e top 21 cm of the hyp ot h e tic a l loam-like
s o i l p r o f i l e ..................................................................................
48
Rela tion between L-band EQSM and s o i l water content
in the top 30 cm of th e hyp o th e tic a l loam-like
s o i l p r o f i l e ..................................................................................
49
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LIST OF FIGURES (continued)
FIGURE
23
24
25
26
27
28
29
30
31
Page
Re la ti ons hi p between L-band e m i s s i v i t y and L-band
EQSM as c a l c u l a t e d by the r a d i a t i v e t r a n s f e r mod el ...
50
Comparison between L-band EQSM and s o i l water con­
t e n t in th e top 21 cm o f the hyp ot h e tic a l loam-like
so il p r o f i l e f or a 2.54 cm r a i n on an i n i t i a l l y dry
p r o f i l e .................................................................................................
52
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm of the hy po th e tic a l loam-like
s o i l p r o f i l e f o r a 2.54 cm r a i n t h a t followed a
previous 2.54 cm r a i n e v e n t.......................................................
53
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm o f the hy po th e tic a l loam-like
s o i l p r o f i l e fo r a 1.27 cm r a i n t h a t followed a
previous 2.54 cm r a i n ev ent .......................................................
54
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm o f the hy p o th e ti ca l loam-like
s o i l p r o f i l e f o r a 5.08 cm r a i n on an i n i t i a l l y dry
p r o f i l e .................................................................................................
55
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm of the hy po th e tic a l loam-like
s o i l p r o f i l e f o r a 5.08 cm r a i n t h a t followed a
previous 5.08 cm r a i n ev ent .......................................................
56
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm o f the hyp ot h e tic a l loam-like
s o i l p r o f i l e f o r a 7.62 cm r a i n on an i n i t i a l l y dry
p r o f i l e .................................................................................................
57
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm o f the hy p ot h e tic a l loam-like
s o i l p r o f i l e f o r a 7.62 cm r a i n t h a t followed a
previous 7.62 cm r a i n e v en t .......................................................
58
Comparison between L-band EQSM and s o i l water con­
t e n t in the top 21 cm o f the hy p ot h e tic a l loam-like
s o i l p r o f i l e f o r a 10.16 cm r a i n on an i n i t i a l l y
dry p r o f i l e ........................................................................................
59
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xiv
LIST OF FIGURES (continued)
FIGURE
32
33
34
35
36
37
38
39
40
Page
Comparison between
t e n t in the top 21
soil profile fo r a
a previous 5.08 cm
L-band EQSM and s o il water con­
cm o f the hyp othetical loam-like
10.16 cm r a i n t h a t followed
r a i n e v e n t ........................................................
60
Rel ationship between s o i l water con te nt in the top
21 cm o f the hypoth et ica l loam-like s o i l p r o f i l e
and L-band e m i s s i v i t y as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r s e le c te d r a i n f a l l e v e n t s .......................
61
Relationship between s o i l water con tent in the top
21 cm of the hypoth et ica l loam-like so il p r o f i l e
and L-band e m i s s i v i t y as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f or a l l simulated r a i n f a l l e v e n t s
63
E f f ec t of s o i l t e x t u r e on
so il water co n te nt in the
t h e t i c a l s o i l s and L-band
by the r a d i a t i v e t r a n s f e r
the r e l a t i o n s h i p between
top 21 cm o f these hypo­
e m is s i v it y as ca l c u la te d
model.............................................
67
X-band and L-band e m i s s i v i t i e s as c a l c u la te d by the
r a d i a t i v e t r a n s f e r model versus time from a 2.54 cm
r a i n on the hypoth et ica l loam-like s o il t h a t was
i n i t i a l l y d r y ....................................................................................
69
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 2.54 cm
r a i n on th e hypoth et ica l loam-like so il t h a t had
pr eviousl y received 2.54 cm of p r e c i p i t a t i o n .................
70
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model vers us time from a 1.27 cm
r a i n on the hypoth et ica l loam-like s o i l t h a t had
prev iously received 2.54 cm o f p r e c i p i t a t i o n .................
71
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 5.08 cm
r a i n on the hy pot he tic al loam-like so il t h a t was
i n i t i a l l y d r y ....................................................................................
72
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 5.08 cm
r a i n on the hypoth et ica l loam-like s o i l t h a t had
prev iou sl y received 5,08 cm o f ... p r e c i p i t a t i o n .................
73
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LIST OF FIGURES (continued)
FIGURE
41
42
43
44
45
46
47
48
49
Page
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 7.62 cm
r a i n on th e hyp othe tical loam-like s o i l t h a t was
i n i t i a l l y d r y ..........................................................................................
74
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 7.62 cm
r a i n on th e hy poth etica l loam-like s o i l p r o f i l e t h a t
had pr evi ous ly received 7.62 cm of p r e c i p i t a t i o n
75
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 10.16 cm
r a i n on the h ypo the tic al loam-like s oi l t h a t was
i n i t i a l l y d r y ....................................................................................
76
X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the
r a d i a t i v e t r a n s f e r model versus time from a 10.16 cm
r a i n on the h ypo the tic al loam-like s o i l t h a t had
p re vio us ly received 5.08 cm o f p r e c i p i t a t i o n .................
77
Re la ti ons hi p between amount o f water added to the
hy po th e tic a l loa m-like s o il p r o f i l e (21 to 150 cm
depth) and the change in e m i s s i v i t y one day a f t e r
the r a i n f o r X-band and L-band...............................................
79
Re la ti o ns hi p between amount of water added to the
h ypo the tica l loam-like s o il p r o f i l e (21 to 150 cm
depth) and the r a t i o o f X-band and L-bandchange in
e m i s s i v i t i e s one day a f t e r the r a i n .....................................
80
R el ati ons hi p between amount of water added to the
h yp oth et ica l loa m- li ke s oi l p r o f i l e (21 to 150 cm
depth) and change in e m i s s i v i t y two days a f t e r the
r a i n f o r X-band and L-band........................................................
81
R e la ti o ns h ip between amount o f water added to the
hyp o th e tic a l loam-like s o i l p r o f i l e (21 to 150 cm
depth) and the r a t i o of X-band and L-band change in
e m i s s i v i t i e s two days a f t e r the r a i n ...................................
82
Generalized flow c h a r t o f the model.....................................
87
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XVI
LIST OF FIGURES (continued)
FIGURE
50
51
52
53
54
55
56
57
58
Page
Re la ti ons hi p between count r a t e and bulk d e n s i t y
f or th e two-probe d e n s i t y gauge determined from
various length aluminum b a r s ...........................................................
94
Approximate pl a n ar geometric shape of gamma-beam,
a f t e r DeVries (1969)............................................................................
99
Soil moisture p r o f i l e s measured in ly s im et e r 3R
during the spring f o r the days shown. J u l i a n day
142 r e p r e s e n t s the s o i l moisture s t a t u s p r i o r to
the
4.3 cm i r r i g a t i o n .................................................................
101
Soil moisture p r o f i l e s measured in l y s im e te r 3R
during the summer f o r the days shown. J u l i a n day
226 r e p r e s e n t s the s o il moisture s t a t u s p r i o r to
the
3.3 cm i r r i g a t i o n .................................................................
102
Soil moisture p r o f i l e s measured in ly s im e te r 3R
during th e f a l l f o r the days shown. J u l i a n day
319 r e p r e s e n t s the s o i l moisture s t a t u s p r i o r to
the
5.4 cm i r r i g a t i o n .................................................................
103
Soil moisture p r o f i l e s measured in ly s im et e r 3R
during th e w in te r f o r the days shown. J u l i a n day
22 r e p r e s e n t s the s o i l moisture s t a t u s p r i o r to
the
3.0 cm i r r i g a t i o n ...............................................................
104
E m i s s i v i t i e s c a l c u l a t e d by the r a d i a t i v e t r a n s f e r
model from measured s o i l water con te nt in l y s im e te r
3R and s o i l temperature f o r the s p r in g , summer,
f a l l , and w in te r experiments....................................................
108
Comparison between measured s o i l water co n t e n t in
the
top 21 cm of the s o i l p r o f i l e in ly s im e te r 3R
and
L-band EQSM as c a l c u l a t e d bythe r a d i a t i v e
t r a n s f e r model from measured s o il water co n te nt
and s o i l temperature f o r the s p r in g , summer, f a l l ,
and w in te r expe rime nts .................................................................
109
R e la ti on sh ip between measured s o i l water c o n t e n t in
th e top 21 cm o f the s o i l p r o f i l e and L-band
e m i s s i v i t y as c a l c u l a t e d by the r a d i a t i v e t r a n s f e r
model f o r s p r i n g , summer, f a l l , and w in te r d a t a .
Inverted s o i l moisture p r o f i l e s were d e l e t e d .................
112
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xv ii
LIST OF FIGURES (continued)
FIGURE
59
60
61
62
63
64
Page
Re la ti on shi p between measured s o il water cont ent in
t h e top 21 cm of the s o il p r o f i l e and L-band
e m i s s i v i t y f o r the spring experiment showing the
algorithm developed from simulated r e s u l t s super­
imposed on the d a t a . Inverted s o i l moisture
p r o f i l e s were d e l e t e d ..................................................................
114
Re la ti ons hi p between measured s o i l water con te nt in
the top 21 cm of the s o i l p r o f i l e and L-band
e m is s i v it y f o r the summer experiment showing the
algorithm developed from simulated r e s u l t s super­
imposed on th e d a t a . Inverted s o i l moisture
p r o f i l e s were.d e l e t e d ..................................................................
115
R el ati on shi p between measured s o i l water c o n t e n t in
the top 21 cm o f the s o i l p r o f i l e and L-band
e m is s i v it y f o r the f a l l experiment showing the
algorithm developed from simulated r e s u l t s su per ­
imposed on the d at a. Inverted s o i l moisture
p r o f i l e s were.d e l e t e d ..................................................................
116
Re la ti ons hi p between measured s o i l water co nt en t in
the top 21 cm o f the s o i l p r o f i l e and L-band
e m i s s i v i t y f o r the winte r experiment showing the
algorithm developed from simulated r e s u l t s super­
imposed on th e d a t a . Inverted s o i l moisture
p r o f i l e s were d e l e t e d ..................................................................
117
Re la ti ons hi p between measured s o i l water c on te nt in
the top 21 cm of the s o i l p r o f i l e and L-band
e m is s i v it y f o r the spr ing experiment inc lud ing
in ve rte d s o i l moisture p r o f i l e s with the al gorithm
developed from simulated r e s u l t s superimposed on
the d a t a ...............................................................................................
119
R el ati ons hi p between measured s o i l water co n t e n t in
the top 21 cm o f the s o i l p r o f i l e and L-band
e m i s s i v i t y f o r the summer experiment inc lud ing
in v e rte d s o i l moisture p r o f i l e s with the algorithm
developed from simulated r e s u l t s superimposed on
the d a t a ...............................................................................................
120
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xviii
LIST OF FIGURES (continued)
FIGURE
65
66
67
68
69
Page
R e la ti on sh ip between measured s o i l water con tent in
th e top 21 cm of the s o il p r o f i l e and L-band
e m i s s i v i t y f o r the f a l l experiment including
in v e r t e d s o i l moisture p r o f i l e s with the algorithm
developed from simulated r e s u l t s superimposed on
th e d a t a ..............................................................................................
121
Re la ti on sh ip between measured s o i l water content in
the top 21 cm of th e s o i l p r o f i l e and L-band
e m i s s i v i t y f o r the w in te r experiment including
in v e rt e d s o i l moisture p r o f i l e s with the algorithm
developed from simulated r e s u l t s superimposed on
the d a t a ..............................................................................................
122
Comparison between measured s o il water con te nt in
the top 21 cm o f the s o i l p r o f i l e and p re d ic te d
s o i l water cont ent from L-band e m i s s i v i t y ca l c u la te d
by the r a d i a t i v e t r a n s f e r model during the spring
experiment f o r (A) 2.31 cm of water ap pl ie d to
ly s im e te r 2C and (B) 4.82 cm of water app lied to
l y s im e te r 3R......................................................................................
125
Comparison between measured s o il water co nt en t in
the top 21 cm o f the s o i l p r o f i l e and p r ed ic te d
s o i l water co n te nt from L-band e m i s s i v i t y c a l c u la te d
by the r a d i a t i v e t r a n s f e r model during the summer
experiment f o r (A) 1.71 cm o f water followed by
1.44 cm o f water applied to ly si m et e r 1L and (B)
2.21 cm o f water followed by 4.80 cm o f water
ap p l ie d to ly si m et e r 1R..............................................................
126
Comparison between measured s o i l water c o n t e n t in
the top 21 cm of the s o il p r o f i l e and p r ed ic te d
s o i l water con tent from L-band e m i s s i v i t y ca l c u la te d
by the r a d i a t i v e t r a n s f e r model during the f a l l
experiment f o r (A) 1.63 cm o f water followed by
6.41 cm o f water applied to ly s im e te r 1R and (B)
6.37 cm of water followed by 3.93 cm o f water
ap pl ie d to ly si m et e r 4R..............................................................
127
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xix
LIST OF FIGURES (continued)
FIGURE
70
71
72
73
74
75
Page
Comparison between measured s o il water co n t e n t in
the top 21 cm of the s o i l p r o f i l e and p r ed ic te d
s o i l water co nt ent from L-band e m is s i v it y c a l c u l a t e d
by the r a d i a t i v e t r a n s f e r model during the winter
experiment f o r (A) 1.58 cm of water followed by
3.09 cm o f water applied to ly s im et e r 1R and (B)
5.17 cm o f water followed by 3.56 cm of water
applied to l y s im e te r 3C..............................................................
128
Relati on shi p between amount o f water added t o the
21 to 150 cm s o i l la y er in the measured s o il p r o f i l e
and th e r a t i o of X-band and L-band change in
e m i s s i v i t i e s f o r the spring experiment with the
algorithm developed from simulated r e s u l t s super­
imposed on the d a t a ......................................................................
132
Rel ationship between amount of water added to the
21 to 150 cm s o i l l a y e r in the measured s o i l p r o f i l e
and the r a t i o o f X-band and L-band change in
e m i s s i v i t i e s f o r the summer experiment with the
algorithm developed from simulated r e s u l t s super­
imposed on the d a t a ........................................................................
133
Relati ons hi p between amount of water added to the
21 to 150 cm s o i l l a y e r i n th e measured s o i l p r o f i l e
and the r a t i o of X-band and L-band change in
e m i s s i v i t i e s f o r the f a l l experiment with the
algorithm developed from simulated r e s u l t s super­
imposed on th e d a t a ........................................................................
134
Re la ti ons hi p between amount o f water added to the
21 to 150 cm s o i l la y e r in the measured s o i l p r o f i l e
and the r a t i o o f X-band and L-band change in
e m i s s i v i t i e s f o r the win ter experiment with the
algorithm developed from simulated r e s u l t s super­
imposed on the d a t a ........................................................................
135
Assumed X-band and L-band p e n e t r a ti o n depths ( s o l i d
l i n e s ) used with empirical approach to esti mat e
em is s i v it y compared to p e n e t r a ti o n depths c a l c u l a t e d
by the r a d i a t i v e t r a n s f e r model f o r X-band ( s h o r t
dashes) and L-band (long d a s h e s ) ...........................................
143
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XX
LIST OF FIGURES (continued)
FIGURE
76
77
78
79
80
81
Page
Rel ationship between e m i s s i v i t y and s o il moisture
co nt en t f o r X-band and L-band rad iom ete rs, a f t e r
Blanchard (1979)...................................................................................
144
Rel ationship between measured s o il water c on te n t in
t h e top 21 cm o f th e s o i l p r o f i l e and L-band
em is si v it y as determined by th e empirical a pp ro ac h. ..
145
Comparison between measured s o i l water c on te nt in
the top 21 cm o f the s o il p r o f i l e and p r e d ic te d so il
water c o n t e n t from L-band e m i s s i v i t y estimated by
th e empirical approach during th e sp rin g experiment
f o r (A) 2.31 cm o f water app li ed to ly s im et e r 2C
and (B) 4.82 cm of water ap p li ed to ly s im et e r 3R
147
Comparison between measured s o i l water co n t e n t in
the top 21 cm o f the s o il p r o f i l e and p r e d ic te d s o il
water co n te nt from L-band e m i s s i v i t y estimated by
the empirical approach during the summer experiment
f o r (A) 1.71 cm of water followed by 1.44 cm of
water applied to ly s im e te r 1L and (B) 2.21 cm of
water followed by 4.80 cm of water ap pl ied to
lys im et e r 1R......................................
148
Comparison between measured s o i l water co nt en t in
the top 21 cm of the s o i l p r o f i l e and pr ed ic te d s o i l
water co nt ent from L-band e m i s s i v i t y estimated by
the empirical approach during th e f a l l experiment
f o r (A) 1.63 cm of water followed by 6.41 cm of
water app lied to l y s im e te r 1R and (B) 6.37 cm of
water followed by 3.93 cm of water app li ed to
ly s im e te r 4R......................................................................................
149
Comparison between measured s o i l water co n t e n t in
the top 21 cm of the s o il p r o f i l e and pr ed ic te d so il
water co n t e n t from L-band e m i s s i v i t y estimated by
the empirical approach during th e w in te r experiment
f or (A) 1.58 cm of water followed by 3.09 cm of
water app lied to ly sim et e r 1R and (B) 5.17 cm of
water followed by 3.66 cm o f water ap pl ied to
ly si m et e r 3C......................................................................................
150
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LIST OF FIGURES (continued)
FIGURE
82
Page
Relati on shi p between amount o f water added to the
21 to 150 cm s o i l la y e r and the r a t i o o f X-band and
L-band change in e m i s s i v i t i e s determined by the
empirical approach o f es ti m at in g e m i s s i v i t y ...................
151
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1
CHAPTER I
INTRODUCTION
A knowledge o f s o i l moisture i s o f p r a c t i c a l importance to th e
a g r i c u l t u r a l i s t f o r growing crops and to the hy.drologist f o r f o r e c a s t i n g
po s si b le flood s.
Some procedures a v a i l a b l e f o r measuring s o i l moisture
are s o il sampling or gr av im et ri c methods, inferences from s o i l pr es su re
p o te n ti a l measured with t e n s i o m e t e r s , neutron s c a t t e r i n g , and gamma-ray
attenuation
(Gardner, 1965).
Unfortunately, a l l o f th e se t e c h n iq u e s ,
except gr avi m etr ic sampling, r e q u i r e c o n s id er a bl e c a l i b r a t i o n and a l l
req uir e r e p l i c a t i o n t o provide r e p r e s e n t a t i v e s o i l moisture dat a.
The
r e s u l t o f any one o f the se methods, re g a r d l e s s o f i t s s o p h i s t i c a t i o n ,
i s a point measurement o f s o i l moisture cont ent .
These poi nt measure­
ments, provided a s u f f i c i e n t number ar e ta ke n, can be used t o e s ti m a t e
so il moisture over la rg e areas by area l e x t r a p o l a t i o n .
However, e x t r a ­
pola tio n o f th e se data i s qu es ti o n a b le due to r a i n f a l l v a r i a b i l i t y
(Dawdy and Bergmann, 1969) and s p a t i a l v a r i a b i l i t y o f s o i l p r o p e r t i e s
(Nielsen e t a l . , 1973).
To b e t t e r understand th e i n t e r a c t i o n o f the b as ic phenomena o c c u r r ­
ing in the s o i l , many r e s e a r c h e r s have modeled the individual processes
o f eva poration, i n f i l t r a t i o n , r e d i s t r i b u t i o n , o r drainage o f s o i l w ate r;
combinations o f t h e s e p r o c e s s e s ; o r t h e whole complex process in an
attempt to b e t t e r es ti m a t e s o i l moisture.
However, use of th e s e models
The c i t a t i o n s on t h i s and the following pages follow the s t y l e
of th e Transactions o f the ASAE.
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2
i s high ly dependent upon the a v a i l a b i l i t y o f c l i m a t i c , s o i l , and
v eg et at i on d a t a .
The inadequate d i s t r i b u t i o n o f meteorological s t a t i o n s
and the e x ce ss iv e c o s t a s s o ci at ed with o bt a in in g th e necessary a n c i l l a r y
data have l i m i t e d th e a p p l ic a t io n of many conventional models.
In
a d d i t i o n , conventional models do not lend themselves to incorporation
of remotely sensed information since they were developed to es timate
s o il water c on te nt in f ix e d , d i s c r e t e l a y e r s .
Advancements in remote sensing techniques withi n the l a s t decade
have provided an economical means of c o l l e c t i n g syno ptic data from
l a r g e ar ea s.
As a r e s u l t , con sidera ble i n t e r e s t has evolved in remote
sensing o f s o i l moisture.
Of the a v a i l a b l e te ch n iq u es , microwave sensors
appear most promising f or th e d et ec ti o n o f s o i l moisture due to t h e i r
g r e a t e r depth o f p e n e t r a ti o n and a l l - w e a t h e r c a p a b i l i t y .
Newton (1977)
s t a t e d t h a t a p as siv e microwave system o p er at in g a t 10.6 GHz (X-band,
2.8 cm wavelength) and 1.4 GHz (L-band, 21 cm wavelength) frequencies
could be implemented to esti mat e n e a r - s u r f a c e (5 t o 20 cm) so il
moisture with promising r e s u l t s .
This i s o f g r e a t s i g n i f i c a n c e , but
a g r i c u l t u r a l i s t s and h yd r ol o gi st s ar e al so i n t e r e s t e d in s o i l moisture
a t g r e a t e r dept hs.
Poe and Edgerton (1972), Blinn and Quade (1972),
and Newton (1977) have in d i ca te d t h a t i t should be p o s s i b le to esti mat e
s o i l moisture a t d i f f e r e n t depths with a multi frequency passive system
by u t i l i z i n g a s u i t a b l e combination of wavelengths.
Such a system
would provide an e s ti m a t e o f the v e r t i c a l d i s t r i b u t i o n o f s o il moisture
withi n a s o i l p r o f i l e .
However, t h e physical s i z e o f th e antennas and
th e la ck o f knowledge o f system response f o r fr e q u e n c i e s l e s s than 1 .4
GHz p r e s e n t l y l i m i t t h i s concept.
The re fo re, a means of determining
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3
soil moist ure a t deeper depths from n e a r -s u rf a c e measurements must be
developed t o meet the needs f o r
measurement of
s o il
moisture in the
deeper p or ti on of th e root zone.
Objective
The o b j e c t i v e of t h i s study was to develop a model to estimate soil
moisture in a t l e a s t two la ye rs of th e r o ot zone from pas sive microwave
measurements r e l a t e d to n ea r - s u r fa ce so il moi stu re.
Measurements of
s o il water cont ent and s o il temperature in ly s im et e rs were used to
v e r i f y th e model.
Approach
The e f f e c t i v e s o il moisture con te nt in some volume of s o i l measured
by microwave radiometers is r e l a t e d to e m i s s i v i t y .
From passive micro­
wave measurements determined a t
freque nci es o f
10.6
e m i s s i v i t y can be ca l c u la te d a t
the time of measurement.
GHz and 1.4 GHz,
The general
equation f o r antenna brigh tn es s temperature i s :
Tg = eTQ + ( l - e )Ts
(1-1)
where atmospheric a t t e n u a t i o n is neglected and
e = e m is s i v it y
Tg = temperature o f the su rf ac e volume (°K)
Tg = sky temperature (°K).
A change in e m is s i v it y can be c a l c u l a t e d from time s e r i e s measurements
f o r each frequency provided th e su rf ac e s o il temperature i s also
measured.
Thus, f o u r po s si b le parameters are a v a i l a b l e t o develop th e
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4
model.
These are:
1) th e e m i s s i v i t y c a l c u l a t e d from X-band radiometer
measurements, s , 2) the e m i s s i v i t y c a l c u l a t e d from L-band radiometer
A
measurements,
e. ,
U
3) the r a t e of change in
change in e^, Ae^.
e
A
, Ae
A
,
and 4) th e r a t e of
Since passive microwave measurements a t the se two
frequencies ar e r e l a t e d t o s o i l moisture in two dynamically changing
so il depths (Newton, 1977) within th e s o il p r o f i l e , i t appears po ssi ble
to develop algorithms to es ti ma te s o i l water con te nt in a ne a r - s u r f a c e
zone and t o es timat e the movement of water in t o the lower r o o t zone
of th e so il p r o f i l e .
This was accomplished by:
1) determining the
incre ase s and subsequent decreases of s o il moisture in the s ur f ac e
laye rs as well as in th e e n t i r e s o il p r o f i l e from v a r ia b le amounts of
applied w ater, 2 ) determining p o s s i b l e responses from two microwave
radiometers (namely X-band and L-band) t o th e e x i s t i n g so il moisture
c o n d i t i o n s , and 3) determining seasonal e f f e c t s on th e above r e l a t i o n s .
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5
CHAPTER II
REVIEW OF LITERATURE
Conventional Soil Moisture Models
Evaporation from s o i l and p l a n t s u r f a c e s i s a major component in
t h e water balance of most watersheds.
are o t h e r major components.
P r e c i p i t a t i o n and i n f i l t r a t i o n
In o rd e r to p r e d i c t ru n o f f , e s ti m at es of
s to r e d wa ter in a s o i l p r o f i l e must be made.
These e s ti m at es ar e
dependent upon a c c u r a te c a l c u l a t i o n s o f p r e c i p i t a t i o n , ev a p o ra ti o n , and
infiltration.
Because o f t h i s , numerous meteorological s o i l moisture
models have been developed throughout pas t y e a r s .
They c o n s i s t of two
t y p e s, those t h a t e s ti m a t e s o il moisture f o r th e e n t i r e s o i l p r o f i l e and
those t h a t es ti m at e th e d i s t r i b u t i o n of s o i l moisture within th e s o i l
p r o f i l e f o r p a r t i c u l a r zones or l a y e r s .
Some o f t h e s e models ar e
b r i e f l y described.
In g e n e r a l, models o f the f i r s t type (Aase e t a l . , 1973; Gumbs and
Byam, 1976; Jensen e t a l . , 1971; Richardson and R i t c h i e , 1973; R it ch ie
e t a l . , 1976) c a l c u l a t e p o t e n t i a l e v a p o t r a n s p i r a t i o n from measured
c l i m a t i c data or from some f unc ti on o f pan e v a p o r a ti o n , a d j u s t t h i s
value to determine an es ti m at e of ac tu al e v a p o t r a n s p i r a t i o n by some
crop and/or s o i l f a c t o r , and then in c o r p o r a te ac tu al e v a p o t r a n s p i r a t i o n
i n t o a water budgeting technique to determine s o i l moi sture.
Potential
e v a p o t r a n s p i r a t i o n i s t h e maximum upward lo s s o f w at er from open w at er ,
wet bare s o i l , or a well watered crop and can be c a l c u l a t e d by a number
o f d i f f e r e n t methods (Penman, 1948; P r i e s t l y and T ay l o r , 1972;
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6
Thornthwaite, 1948; Van Bave l, 1966).
Jensen e t a l . (1971) and Gumbs
and Byam (1976) developed models f o r i r r i g a t i o n scheduling purposes
o r f o r wate r management t o obtain optimum crop growth.
Use o f t h e i r
models assumes t h a t an adequate supply o f wa ter always e x i s t s in the
soil profile.
ar ea s.
However, t h i s i s not always th e case in many a g r i c u l t u r a l
When s o i l w at er i s l i m i t e d , p l a n t evaporation i s reduced.
Richardson and R it c h i e (1973) solved t h i s problem by e s ti m at in g s o il
evaporation and p l a n t evaporation s e p a r a t e l y .
They used a number of
e m p i r i c a l l y derived r e l a t i o n s h i p s r e q u i r i n g l e a f area index and para­
meters based on physical c h a r a c t e r i s t i c s o f th e s o i l to esti mat e s o il
and p la n t evap or atio n.
A s o i l water c o e f f i c i e n t based on the percentage
o f a v a i l a b l e water i n t h e p r o f i l e a t a given time was in co rpor at ed in t o
the model developed by Aase e t a l . (1973) in or de r to es ti m a t e evapora­
ti o n under l i m i t i n g s o i l water c o nd it io ns .
R it c h ie e t a l . (1976)
modified a cropland evapo ra tio n model ( R i t c h i e , 1972) t o c a l c u l a t e
evaporation from n a t i v e grass land s and, th u s , p r e d i c t s o i l moisture.
The model c o n s i s t s o f t h r e e p a r t s :
th e c a l c u l a t i o n of evaporation from
s o i l , th e c a l c u l a t i o n o f t r a n s p i r a t i o n f o r un li mi te d s o i l w a te r, and
the c a l c u l a t i o n o f t r a n s p i r a t i o n under l i m i t e d s o i l water c on di tio n s .
This model al so uses l e a f are a index and s o i l hy draulic p r o p e r ti e s in
a d d i t i o n t o th e c l i m a t i c da t a req ui re d t o c a l c u l a t e p o t e n t i a l evapora­
tion.
More exact budgeting techniques (Baier and Robertson, 1966;
Bordovsky, 1978; Saxton e t a l . , 1974; S e l i r i o and Brown, 1971) have
been developed to e s ti m a t e th e movement and d i s t r i b u t i o n o f s o il
moisture in th e s o i l p r o f i l e on a l a y e r - b y - l a y e r b a s i s .
Baier and
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Robertson (1966) developed a new budgeting technique which they
r e f e r r e d to as th e v e r s a t i l e budget.
The a v a i l a b l e water in th e s o i l
p r o f i l e was divided i n t o s i x a r b i t r a r y zones containing 5 .0 , 7 . 5 , 12.5,
25.0, 25.0 and 25.0 percent o f th e t o t a l , r e s p e c t iv e l y .
Soil wate r i s
simultaneously e x t r a c t e d from d i f f e r e n t depths of th e s o il p r o f i l e
permeated by roots in r e l a t i o n to th e r a t e of p o t e n t i a l e v a p o t r a n s p i r a ­
t i o n and th e a v a i l a b l e s o i l moisture in each zone.
Incorporated i n t o
t h e model ar e crop c o e f f i c i e n t s , adjustments to the se c o e f f i c i e n t s f or
l i m i t e d s o i l wa ter c o n d i t i o n s , d i f f e r e n t types of s o i l drying curv es,
e f f e c t of d i f f e r e n t atmospheric demand r a t e s on the actual evapotransp i r a t i o n / p o t e n t i a l e v a p o t r a n s p ir a ti o n r a t i o , an esti mat e o f i n f i l t r a t i o n ,
and adjustments f o r r u n o f f and drainage.
The b a s ic ideas o f th e v er s a­
t i l e budget were r e t a i n e d by S e l i r i o and Brown (1971).
They accounted
f o r the simultaneous withdrawal o f s o i l water from a l l zones by
a s s ig n in g a pr o por ti on o f t h e d a i l y p o t e n t i a l evaporation t o each zone
according to an e x t r a c t i o n p a t t e r n .
This e x t r a c t i o n p a t te r n was
developed by comparing es timat ed s o il moisture with actual measurements.
Saxton e t a l . (1974) modeled th e v e r t i c a l movement o f water i n t o , w i t h i n ,
and out o f a s o i l - w a t e r - p l a n t system.
twelve 15 cm t h i c k l a y e r s .
The so il p r o f i l e was divided int o
Three major sequences were involved:
1) c a l c u l a t i n g ac t u a l e v a p o t r a n s p i r a t i o n and withdrawing i t from e x i s t ­
ing s o il moi stu re, 2) adding i n f i l t r a t i o n to the s o i l w ate r, and
3) r e d i s t r i b u t i n g th e s o i l moisture.
Model c a l c u l a t i o n s were on a day-
to-day b as is with d a i l y input s of p o t e n t i a l e v a p o t r a n s p ir a ti o n ,
i n f i l t r a t i o n , and p l a n t canopy d at a.
Output was a s o i l moisture p r o f i l e
with a value to r e p r e s e n t each la y e r .
Bordovsky (1978) developed a s o i l
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8
moisture balance model to p r e d i c t wet or dry days f o r farming opera tion s
based on the s o i l moisture content in the top 15 cm o f th e s o i l p r o f i l e .
The s o i l p r o f i l e was divided int o 5 la y e rs which were 15 cm, 15 cm,
30 cm, 30 cm, and 60 cm t h i c k , r e s p e c t i v e l y .
Daily s o i l moisture was
c a l c u l a t e d in fo u r st eps which accounted f o r changes in s o i l moisture
due t o i n f i l t r a t i o n and drainage, s o i l e va po ra tio n , p la n t evap ora tion,
and moisture r e d i s t r i b u t i o n .
Model in pu ts include r a i n f a l l , d a i l y
s o l a r r a d i a t i o n , mean a i r temperature, s o i l hy d rau li c c h a r a c t e r i s t i c s ,
l e a f area index, and th e upper l i m i t o f s o i l moisture f o r each la ye r .
The pr ev io us ly mentioned models have e i t h e r been completely
empirical in n a t u re or have contained some degree o f empiricism.
Numerous t h e o r e t i c a l models e x i s t f o r the s o l u t i o n of th e s o il water
flow equation involving i n f i l t r a t i o n , r e d i s t r i b u t i o n , d rai na ge, o r
evaporation by numerical techniques.
Freeze (1969) and Reid (1977)
pres ent e x c e l l e n t reviews o f the se methods.
Hanks e t a l . (1969)
described a g en er a li ze d numerical technique f o r th e simultaneous estima­
t i o n of i n f i l t r a t i o n , r e d i s t r i b u t i o n , drain ag e, and evaporation as they
occur under f i e l d c o n d i ti o n s .
Input data include hydr aul ic co n d u c t iv it y
of th e s o i l as a function o f moisture c o n t e n t, p res su re head as a
function of moisture content f o r w ett ing and drying c y c l e s , i n i t i a l
pressure head as a function o f depth, and p o t e n t i a l f lu x as a function
of time.
Other inputs include the s i z e o f th e depth increment, the
i n i t i a l time increment to be used, upper and lower l i m i t s o f pressure
head and water c o n t e n t , lower boundary c o n d i ti o n s , and length o f computa­
ti on time.
Output is the s o i l water con te nt a t each depth increment f o r
a given time s t e p .
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A numerical model o f s o i l - w a t e r dynamics was w r i t t e n in the Con­
tinuous System Modeling Program (CSMP) computer language to simulate the
processes of i n f i l t r a t i o n , dr ain ag e, evap ora tion, and water storage
( H i l l e l , 1975; H i l l e l and Van Bavel, 1976) f o r uniform s o il p r o f i l e s .
Inputs to the model c o n s i s t o f the number o f compartments or lay ers in
which to d iv i d e the s o il p r o f i l e , i n i t i a l volumetric moisture content of
the p r o f i l e , d a i l y p o t e n t i a l eva po ra tio n, hydr aul ic c h a r a c t e r i s t i c s of
the s o i l , s o i l p o r o s i t y , and s a t u r a t e d hyd raulic c o n d u c t iv it y . Soil mois­
tu r e content f o r each la y e r is p r in t e d out a t s p e c i f i e d times.
H ill el
and Talpaz (1977) extended t h i s model to simulate layered p r o f i l e s .
The f i r s t vers ion o f the s o i l - w a t e r dynamics model ( H i l l e l , 1975)
was modified by Van Bavel and H i l l e l (1975, 1976) to simultaneously
simulate the flow o f h e a t and moisture in a v e r t i c a l s o il p r o f i l e .
In­
puts to t h i s model were hourly or d a i l y c l i m a t i c data ( s o l a r r a d i a t i o n ,
a i r and dewpoint te mp era tu res , windspeed, day length and r a i n f a l l ) , s o i l
hydraulic c h a r a c t e r i s t i c s , an i n i t i a l moisture co nt en t p r o f i l e , an i n i ­
t i a l s o i l temperature p r o f i l e , a t a b l e of s u rf ac e albedo versus moisture
c o n t e n t, a t a b l e o f s o i l temperature versus he at c o n d u c t iv it y by water
vapor, thermal p r o p e r t i e s o f the s o i l , s o il p o r o s i t y , and s a t u r a t e d
hydraulic
co n d u c t iv it y .
Model outp ut c o n s i s t s of s o i l moisture cont ent
and so il temperature f o r each la y e r a t the s p e c i f i e d time.
From t h i s b r i e f overview o f e x i s t i n g water balance models, i t can
be seen t h a t as the models become more complex, ad d i ti o n a l inp ut data
are re qu ire d.
Un fo rtu na te ly , many o f these conventional models are
limi te d in a p p l i c a t i o n due to the excessive c o s t a s s o ci at ed with o b t a i n ­
ing the necessary a n c i l l a r y da ta .
As mentioned e a r l i e r in t h i s d i s s e r t a ­
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10
tion,
remote sensing has proved to be an economical method f o r o b ta in ­
ing data from l a r g e are a s.
Consequently, many experiments have been
conducted t o d e t e c t s o i l moisture by various remote sensing techniques.
Due to th e physics o f el ectrom agnetic th e o ry , remote sens ing measure­
ments are l i m i t e d by th e dynamic depth o f p e n e t r a t i o n which i s dependent
upon the wavelength o f the sen so r.
In o t h e r words, sensors operating
in the v i s i b l e and i n f r a r e d region o f th e electr om agn etic spectrum
d e t e c t s u r f ac e phenomena only.
Microwave sensors with wavelengths of
1.55 cm and lon ge r have the a b i l i t y to p e n e t r a t e th e s o i l s u r f a c e .
Thus., these sen so rs may provide input to s o i l moisture models i f the
dynamic depth being sensed can be taken i n t o account.
Remote Sensing o f Soil Moisture
Attempts t o measure s o il moisture on fallow f i e l d s with several
types of a e r i a l photographic films (Sewell and A ll e n , 1973) met with
l i m it e d r e s u l t s .
They found t h a t the c o l o r i n f r a r e d fil m enhanced the
c o n t r a s t between o b je c ts as s o c ia t e d with s u r f a c e s o i l moisture
d if f e r e n c e s and gave b e t t e r o ve r al l r e s u l t s than the black and white i n ­
f r a r e d film o r th e r e g u l a r co lo r f il m .
Sewell and Allen (1973) conclud­
ed t h a t the d e t e c t i o n and c l a s s i f i c a t i o n o f f al l o w f i e l d s o i l moisture
using normal and i n f r a r e d films as sensors was f e a s i b l e over the so il
moisture range i n v e s t i g a t e d (approximately one t o tw ent y-f ou r percent
dry weight).
However, problems with varying cloud cover, lack o f
p e n e t r a t i o n , d i f f e r e n t sun an g l e s, d i f f e r e n c e s between film l o t s , and
d if f e r e n c e s in f i l m processing may ad ver se ly a f f e c t a e r i a l i n f r a r e d
photographic techn ique s.
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Measurements of thermal i n f r a r e d emission from bare s o i l hold con­
s i d e r a b l e promise f o r es ti ma ti ng s o i l moisture.
Idso and hi s co­
workers (1975, 1976) have conclusively shown t h a t emitted thermal
i n f r a r e d r a d i a t i o n i s i n d i c a t i v e of s o il moisture w ithin the la y e r of
s o i l t h a t in f lu en ce s s u rf a c e so il temperature even though th e thermal i n ­
f r a r e d wavelengths cannot p e n e t r a t e the s u r f a c e .
The amplitude of the
d a i l y diurn al s u r f a c e s o i l temperature wave versus volumetric water con­
t e n t r e l a t i o n s h i p was found to be dependent upon s o il type (Idso e t a l . ,
1975).
However, t h i s e f f e c t i s minimal i f s o i l water is expressed in
u n i t s o f p res su re p o t e n t i a l .
Unfortunately, th e s e concepts have
l i m i t a t i o n s s in ce p r a c t i c a l l y a l l work has been s i t e - s p e c i f i c under
c l e a r sky c o n d i ti o n s .
Microwave se nsors are capable o f measuring through cloud cover and
some r a in when s u f f i c i e n t l y long wavelengths ar e used.
Measurement is
almost independent o f th e weather a t th e lower freque nci es (0.4 to 10
GHz).
Thus, microwave sensors are unique in t h e i r c a p a b i l i t y to
provide timely information under cond itions when o t h e r sensors are
rendered inoperable by the weather (Moore e t a l . , 1975).
Numerous experiments have been undertaken to develop and t e s t
microwave equipment f o r measuring s o i l moisture (Blanchard, 1972;
Schmugge e t a l . , 1974, 1976).
These experiments were attempts t o
c o r r e l a t e ai rb or n e pas sive microwave system response t o ground measure­
ments o f s o i l mo isture.
Blanchard (1972) concluded t h a t X-band antenna
temperatures showed some c o r r e l a t i o n with s o i l moisture in th e su rf ac e
layers o f s o i l .
Schmugge e t a l . (1974) demonstrated t h a t i t was
po s si b le to observe pas sive microwave antenna b r ig h t n e s s temperature
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12
v a r i a t i o n s produced by changes in s o i l moisture with a i r c r a f t - b o r n e
microwave radiometers f ly i n g over unvegetated t e r r a i n .
They concluded
t h a t the response i s a fu n cti on of radiometer wavelength and the
d i s t r i b u t i o n o f moist ur e in th e s o i l .
For the 1.55 cm wavelength r a d i o ­
meter, the emission was observed to be a l i n e a r f u nct io n o f s o il moisture
over the range from zero t o 35 percent by weight.
The 21 cm wavelength
radiometer produced l i t t l e or no v a r i a t i o n in emission f o r s o i l moisture
values below 10 or 15 percent moisture con te nt by weight.
Above t h i s
value, the emission decreased l i n e a r l y with increased s o il moi stu re.
Soil moisture co n te nt was determined from a s e r i e s of la y e r s within the
s u r f ac e 15 cm o f s o i l .
I t was a l s o observed t h a t no appa re nt d i f f e r e n c e
was in d i c a t e d between the two s o i l types in v e s t i g a t e d a t the 1.55 cm
wavelength; whereas, the 21
cm wavelength radiometer responded
d i f f e r e n t l y to the two s o il types.
The e f f e c t o f s o i l t e x t u r e on th e emission from th e s e s o i l s was
s tud ie d by Schmugge e t a l . (1976).
I t was found t h a t t h i s e f f e c t can
be compensated f o r by expressing s o i l moisture as a perce nt o f f i e l d
c ap a c it y f o r the s o i l .
This r e s u l t in di cat ed t h a t the microwave emis­
sion is influen ced only by the a v a i l a b l e water in the
s o i l as opposed
to th e t o t a l water c o n t e n t .
1.55 cm wavelength
They a l s o found t h a t the
radiometer was responding to s o i l moisture in the top few m i ll i m e t e r s
of the s o i l .
In comparing the 21 cm r e s u l t s with the
1.55 cm r e s u l t s ,
Schmugge e t a l . (1976) found a g r e a t e r range o f br ig ht ne s s temperatures
observed a t 21 cm wavelength than a t 1.55
in a g r e a t e r s e n s i t i v i t y to
cm wavelength.
This r e s u l t s
s o i l moisture a t the longer wavelength.
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Several well c o n t r o l l e d experiments using ground based microwave
radiometers have been conducted (Blinn and Quade, 1972; Newton, 1977;
Poe and Edgerton, 1972).
Results from such an experiment (Newton, 1977)
i n d i c a te t h a t measurement of s o il moisture in the top one to two cm in
bare s o i l i s f e a s i b l e with a s h o r t wavelength (X-band, 2.8 cm) passive
microwave sensor.
Newton (1977) a l s o found t h a t th e L-band (21 cm
wavelength) dual p o la ri ze d passive microwave radiometer could e f f e c ­
t i v e l y be used to measure "equ ivalent s o il moisture" which in r e a l i t y
is the a v a i l a b l e water in th e s o i l .
This was accomplished by using the
d if f e r e n c e between the v e r t i c a l and the horizontal antenna temperature
measurements a t 35 degrees o f f na di r to estimate s u rf ac e roughness.
The
horizontal antenna temperature measurement a t 20 degrees o f f n a d i r was
then used t o e s t i m a t e an average volumetric soil mo isture co n t en t.
This
average s o i l moi st ure from some s u rf ac e la y e r as determined by the L-band
radiometer was estimated to f a l l with in a nine percent window f o r smooth
and medium rough s u r f ac es and to with in an 11 to 12 percent window f o r
rough s u r f a c e s .
The unique d i e l e c t r i c p r o p e r t i e s of water a t microwave wavelengths
affo rd th e p o s s i b i l i t y f o r remotely sensing soil moisture in th e n e a r ­
surface s o i l l a y e r s .
The d i e l e c t r i c c o n s ta n t f o r water (around 80) is
an order of magnitude l a r g e r than t h a t of dry s o i l s (approximately 5)
a t microwave f r eq ue nc ie s (Schmugge e t a l . , 1974).
The amount of energy
generated a t any p o i n t w it h i n the s o i l volume i s dependent upon the d i ­
e l e c t r i c co n s ta n t o f the s o i l water mixture ( s o i l moisture) and the s oi l
temperature a t t h a t po in t.
As energy propagates upward through the s oi l
volume from i t s p o in t of o r i g i n , i t i s a f f e c t e d by th e d i e l e c t r i c ( s o i l
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14
moisture) g r a d i e n t along th e path o f propagation.
The t o t a l energy
t h a t u l t i m a t e l y cr o ss es th e so il s u r f ac e i s a weighted in t e g r a l of
th e energy em itt ed a t various points withi n th e s o i l volume.
The depth
of the emitted r a d i a t i o n and the subsurface e x t e n t o f the weighting
function are frequency
dependent, t h u s , lower frequencies are s e n s i t i v e
to d i e l e c t r i c p r o p e r t i e s a t g r e a t e r depths in th e s o i l (Schmugge e t a l . ,
1978).
Newton (1977) found t h a t th e L-band radiometer measures s o il
moisture in a depth ranging from th e s u r f ac e few centimeters f o r
s a t u r a t e d co nd it ion s t o approximately 20 cm when th e average s o i l
moisture in t h e p r o f i l e i s around e i g h t pe r ce n t by volume.
The depth
sensed by the L-band system was l i n e a r l y r e l a t e d to the weighted average
moisture in the p r o f i l e .
Newton (1977) concluded from his study t h a t a passive microwave
system o p er at in g a t 10.6 GHz and 1.4 GHz freque nci es showed p o te n ti a l
fo r es ti m at in g th e n e a r - s u r f a c e s o i l moisture cont ent .
Such a measur­
ing system would provide an average s o il moisture content a t two
dynamic depths in th e s o i l p r o f i l e .
However, i f a g r i c u l t u r a l i s t s and
h ydr olo gi sts intend to use remotely sensed s o i l moisture d a t a , t h e r e
must be a means f o r determining s o i l moisture con tent a t deeper depths
from n e a r - s u r f a c e measurements.
As prev iou sl y s t a t e d , passive
microwave measurements r e l a t e d to n e a r - s u r f a c e s o i l moisture content
should provide in p ut s to a model t h a t w i l l e s ti m a t e s o i l moisture in
portions o f th e r o o t zone.
C ih l a r and Ulaby (1975) and Reid (1977) have hypothesized on
p os si b le ways to es ti m a t e s o i l moisture using microwave measurements.
The s i t e - s p e c i f i c algorithm suggested by C ih l a r and Ulaby (1975) was a
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15
s o i l wa ter balance equation r e q u i r i n g inputs o f p r e c i p i t a t i o n , ru n o f f ,
a ct u al evaporation or actu al e v a p o t r a n s p i r a t i o n , and drainage to
es ti m at e th e moisture cont ent in th e s o i l p r o f i l e .
Microwave sensors
would only provide an e s ti m at e o f th e ac t u al p r e c i p i t a t i o n p a t t e r n over
the a r e a .
They a l s o des cri be d how a m u l t i - l a y e r model, such as th e one
by Baier and Robertson (1966), could be divi ded in t o a s e r i e s of one
ce n t im e te r t h i c k la y er s to e s ti m a t e a s o i l moisture p r o f i l e .
Reid
(1977) described how microwave remote se nsing data could be used to
update a s o i l moisture model ( H i l l e l , 1975) and improve th e sim ul ati on.
Microwave measurements could be compared to th e model p r e d i c t i o n s of
s o i l moisture in the upper s o i l l a y e r s ; i f any di s c re p a n c ie s e x i s t e d ,
th e microwave measurements would be used to update the model.
Reid
(1977) s t a t e d t h a t d i s c r e p a n c i e s , i f any, would be a t t r i b u t e d to e r r o r s
in the s p e c i f i c a t i o n s of s o i l p r o p e r t i e s an d /o r e r r o r s in the input
meteorological da ta .
These approaches to e s ti m a t in g s o i l moisture using microwave
measurements r e q u i r e excessive amounts o f a n c i l l a r y dat a.
A model t h a t
e s ti m at es s o i l moisture from microwave measurements should use those
measurements only and not r e l y on d at a d es c r ib i n g s o il p r o p e r t i e s and
climatic variables.
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16
CHAPTER I I I
THEORETICAL DEVELOPMENT OF THE MODEL
Theoretical models were used to si mu la te s o il moisture p r o f i l e s
and microwave e m i s s i v i t i e s f o r a homogeneous, i s o t r o p i c s o il with a
smooth, bare s u r f a c e .
exist.
From a p r a c t i c a l viewpoint, such a s o il does not
However, t h i s ideal case was s e l e c t e d to simplify the develop­
ment of a model to p r e d i c t s o il water c o n t e n t in two la y er s of the r o o t
zone from microwave radiometer measurements r e l a t e d to n e a r - s u r f a c e
s o il moisture.
Procedure
To s a t i s f y th e proposed o b j e c t i v e , two area s were addressed.
were:
These
1) to develop a s e r i e s of s o i l moisture p r o f i l e s t h a t would be
expected from p r e c i p i t a t i o n o f varying amounts on s o i l t h a t was dry,
moderately m o i s t , or near f i e l d ca p a c it y and 2) to c a l c u l a t e th e thermal
microwave emission from t h i s s e r i e s of s o i l moisture p r o f i l e s .
A simul ati on model f or c a l c u l a t i n g th e water content and tempera­
t u r e p r o f i l e s o f a bare s o i l (Van Bavel and H i l l e l , 1975, 1976) was
used t o develop th e t i m e - s e r i e s of s o i l moisture p r o f i l e s .
is presented in d e t a i l by Van Bavel and Lascano (1979).
The model
I t is a dynamic
model; th us , th e p r o p e r t i e s of the s o il system ar e continuously updated
as th e temperature and water content change with time.
A comprehensive
method f or th e simultaneous so lu ti o n of th e c o n t i n u i t y equation fo r
water and heat flow i s provided in th e model.
The s o lut io n is obtained
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17
a t f r e q u e n t , fixed i n t e r v a l s , and th e moisture and temperature p r o f i l e s
are p r in t e d when d e s i r e d .
A c h a r a c t e r i s t i c o f t h i s model t h a t d i s ­
t i n g u is h e s i t from o t h e rs i s t h a t i t does not assume an average evapora­
t i o n r a t e but r a t h e r gene ra tes the ins tantaneous r a t e from ambient
weather co ndi tio ns and momentary values of s o i l moisture and temperature.
This model i s w r i t t e n in the Continuous System Modeling Program I I I
(CSMP I I I ) language (IBM, 1975) which is a s p e c i f i c numerical simulation
language s u i t a b l e f o r t i m e - v a r i a n t systems.
Inputs to the model are o f two types:
c o ns ta nt and v a r i a b l e .
Constant inputs r e f e r to the hydr aul ic c h a r a c t e r i s t i c s of the s o i l and
the r e l a t i o n s h i p between albedo and volumetric moisture cont ent o f the
s ur fac e.
The hyd raulic c h a r a c t e r i s t i c s o f the s o i l d es cr ib e the r e l a ­
t i o n between s o il p r e s s u re p o t e n t i a l and hydraulic co nd u ct iv it y to
volumetric water co n t e n t.
Variable inputs r e f e r to the time-dependent
c l im a t ic data which a r e d a i l y s o l a r r a d i a t i o n (MJ/m2 j a y ^ ’ maxirnum ancl
minimum a i r temperature (°C), maximum and minimum dewpoint temperature
( °C), average d a i l y windspeed (m/s), amount o f p r e c i p i t a t i o n (mm), storm
du ration ( h r ) , and daylength ( h r ) .
Other values t h a t must be known are
the i n i t i a l s o il moisture co nt ent and s o i l temperature p r o f i l e s .
The s o i l s e l e c t e d f o r t h i s study was a hyp othetical loa m-like,
homogeneous s o i l .
The assumed s o i l moisture c h a r a c t e r i s t i c (p ressure
p o te n ti a l versus volumetric moisture con tent) i s shown in Fig. 1.
This
function was derived from empirical r e l a t i o n s developed by Clapp and
Hornberger (1978).
However, t h i s procedure produced a r e l a t i o n s h i p t h a t
was u n r e a l i s t i c f o r the dry p o rt i o n o f th e f u n c ti o n .
To improve the
r e l a t i o n s h i p , values s i m i l a r t o the c h a r a c t e r i s t i c s o f an Adelanto loam
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18
CONDUCTIVITY
(M/S)
—1
HYDRAULI C
LU
(—
LU
PRESSURE POTENTIAL
HYDRAULIC CONDUCTIVITY
0.1
WAT E R C O N T E N T
0.2
0.3
0.4
( V O L U ME F R A C T I O N )
FIG. 1. Re la ti on sh ip between s o il pressure p o t e n t i a l and volumetric
moisture content (Clapp and Hornberger, 1978) f o r th e hypothetical
loam-like s o i l . Hydraulic c o n d u c t i v i t y versus volumetric moisture
content was c a l c u l a t e d a f t e r Jackson (1972).
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19
(Jackson, 1964) were s u b s t i t u t e d f o r th e e m p i r i c a l l y derived pressure
p o t e n t i a l s below -150 m.
The corresponding hyd rau li c co nd uc ti v it y
function was derived following Jackson (1972).
shown in Fig. 1 (p. 18).
This f u n ct io n i s al so
Saturated moisture co n t e n t and s a t u r a t e d
8 3
-5
hydraulic c o n d u c t iv it y were taken as 0.391 m /m and 0.694 x 10
m/s,
respectively.
Climatic data used as inp ut to the model r ep r es en te d th e h o t t e s t
period during the summer o f 1978 a t College S t a t i o n , Texas.
These data
were recorded a t the Texas A&M University A gr ic u lt u r al Engineering
ly si m et e r i n s t a l l a t i o n .
S olar r a d i a t i o n was measured with an Eppley
black and white pyranometer.
Air temperature and dewpoint temperature
were measured with copper-constantan thermocouples i n s t a l l e d in an
aspirated radiation shield.
Dewpoint temperature was i n f e r r e d from the
bobbin c a v i ty temperature o f a dewprobe.
a three-cup anemometer.
Windspeed was measured with
Sensor output was recorded continuously by a
data logger (Model CR5, Campbell S c i e n t i f i c , I n c . ) .
I nt eg r a te d t o t a l s
of s o l a r r a d i a t i o n and windspeed and i n t e g r a te d averages of a i r and
dewpoint temperature were p rin te d hourly.
Daylength was determined
from s u n r i s e - s u n s e t t a b l e s f o r College S t a t i o n , Texas.
The top 1.5 m of the s o i l p r o f i l e was divided in t o 28 la y er s as
shown in Table 1.
Boundary co nd it ion s a t th e bottom la y e r o f the s o i l
p r o f i l e were defined as fo ll ow s:
1) the water fl u x a t the boundary was
taken to be equal to the hydraulic co nd u ct iv it y o f the l a s t la y e r which
i s eq ui v al en t t o u n i t hy draulic p o t e n t i a l g r a d i e n t , and 2) the heat flow
a t the boundary was c a l c u l a t e d by F o u r i e r ' s law, assuming the tempera­
tu re a t 1.50 m remained c o n s ta n t .
The temperature a t t h i s depth was
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20
TABLE 1.
GEOMETRY OF SIMULATED SOIL SYSTEM
Layer
Number
Layer
Thickness
(m)
Depth to
Center of Layer
(m)
1
0.010
0.005
2
0.010
0.015
3
0.010
0.025
4
0.010
0.035
5
0.010
0.045
6
0.010
0.055
7
0.010
0.065
8
0.010
0.075
9
0.010
0.085
10
0.010
0.095
n
0.010
0.105
12
0.010
0.115
13
0.010
0.125
14
0.010
0.135
15
0.010
0.145
16
0.020
0.160
17
0.020
0.180
18
0.020
0.200
19
0.020
0.220
20
0.020
0.240
21
0.050
0.275
22
0.050
0.325
23
0.100
0.400
24
0.150
0.525
25
0.150
0.675
26
0.150
0.825
27
0.300
1.050
28
0.300
1.350
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21
s e t equal to the i n i t i a l temperature o f th e lowest l a y e r from the i n i t i a l
temperature p r o f i l e inp ut to the model.
The r a i n f a l l ge n era to r fu n c ti o n in th e model assumes a t r i a n g u l a r
d i s t r i b u t i o n with a base equal t o the du ra ti o n of th e event and a h ei gh t
equal t o twic e th e average r a i n f a l l i n t e n s i t y .
ev en t, the following inputs ar e needed:
To simulate a r a i n
1) th e beginning and ending
times (hr) o f the event and 2) the t o t a l r a i n f a l l amount (mm).
From
t h i s , the r a i n f a l l gene ra tor fu n cti o n c a l c u l a t e s the base, midpoint
and h ei g ht o f th e t r i a n g u l a r d i s t r i b u t i o n t o make the area of the
t r i a n g l e equal the t o t a l r a i n f a l l amount.
Thus, the r a i n f a l l r a t e
s t e a d i l y i n c re a s e s from zero to i t s maximum i n t e n s i t y and then s t e a d i l y
decre ases back to zero.
Rainfall events t h a t were simulated to produce the necessary s o i l
moisture p r o f i l e s ar e shown in Table 2.
An average r a i n f a l l i n t e n s i t y
o f 3.8 cm/hr was used in a l l simu latio ns to determine r a i n f a l l d u r a t i o n .
The model assumes t h a t th e volume of water ap p li ed to the s o i l su rf ac e
i n f i l t r a t e s ; i . e . , t h e r e i s no run of f.
With th e exception o f two c a s e s ,
the simul ati on began on Ju li a n day 196 and ran through day 241 f o r a
period of 47 days.
occurred.
During t h i s period o f time, two r a i n f a l l events
J u l i a n day 202 through day 241 defined the simulation period
f o r th e o th e r two cases in which th e re were t h r e e r a i n f a l l events (see
Table 2).
The f i r s t r a i n f a l l always occurred on a very dry p r o f i l e .
All si mu la ti on s were s t a r t e d a t midnight one day p r i o r to the day o f
r a i n f a l l to allow f o r p r o f i l e e q u i l i b r a t i o n s in c e the i n i t i a l s o il
moisture and s o i l temperature p r o f i l e s were assumed and not measured
quantities.
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TABLE 2.
Simulation
Run
SIMULATION PERIOD AND ASSOCIATED RAINFALL EVENTS
Description of
Rain Event
Time Period
( J u l i a n Date)
Day of
Rain
Cl
C2
C3
202-211
212-230
232-241
203
213
233
2.54 cm on dry p r o f i l e
2.54 cm
1.27 cm
D1
D2
D3
202-211
212-230
232-241
203
213
233
2.54 cm on dry p r o f i l e
7.62 cm
1.27 cm
El
E2
196-211
212-241
197
213
5.08 cm on dry p r o f i l e
2.54 cm
n
12
196-211
212-241
197
213
5.08 cm on dry p r o f i l e
5.08 cm
FI
F2
196-211
212-241
197
213
5.08 cm on dry p r o f i l e
7.62 cm
SI
S2
196-211
212-241
197
213
5.08 cm on dry p r o f i l e
10.16 cm
G1
G2
196-211
212-241
197
213
7.62 cm on dry p r o f i l e
2.54 cm
HI
H2
196-211
212-241
197
213
7.62 cm on dry p r o f i l e
7.62 cm
R1
R2
196-211
212-241
197
213
10.16 cm on dry p r o f i l e
5.08 cm
Q1
196-211
212-241
197
213
11.43 cm on dry p r o f i l e
13.97 cm
Q2
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Volumetric s o i l moisture con tent and s o i l temperature were prin te d
a t 1400 hours (2:00 p.m.) f o r each day of t h e sim ulation.
The 2:00 p.m.
p r i n t o u t was s e le c te d in o rd er t o obtain th e maximum change in moisture
con te nt from day t o day.
Daily s o i l moisture contents f o r each simula­
t i o n were examined; days t h a t showed l e s s than one percent by volume
change in n e a r - s u r f a c e s o i l moisture were not considered in f u r t h e r
analysis.
Simulated so il moisture co nt ent and s o i l temperature f o r the
se le c te d days were input t o a r a d i a t i v e t r a n s f e r model (Newton, 1977).
This model c a l c u l a t e s th e r a d i a t i o n produced within th e so il volume
from e x i s t i n g s o il moisture and s o il temperature c o nd it io n s .
That i s ,
i t c a l c u l a t e s the emission t h a t would be expected to be measured by
microwave radiometers.
included.
Ef fe c ts of th e s u r f a c e - t o - a i r i n t e r f a c e are not
Assumptions underlying t h e emission model are:
1) the soil
volume i s modeled as a h o r i z o n t a l l y , pl an e, s t r a t i f i e d medium with each
la y e r c o n s i s t i n g of a n o n - s c a t t e r i n g homogeneous s o i l , 2) so il d i e l e c t r i c
and so il temperature are c o n s ta n t through any given la y er of s o i l , and
3) the s o il su rf ac e and l a y e r i n t e r f a c e s ar e smooth.
A b r i e f d e s c r i p t i o n o f the model fo llows.
Inputs to th e r a d i a t i v e
t r a n s f e r model c o n s i s t of s o i l moisture ( e i t h e r g r av im et r ic or volu­
metric) and s o i l temperature s p e c i f i e d a t various dept hs, so il type
being modeled, and s o il depth to which the c a l c u l a t i o n s are t o be pe r ­
formed.
I f gr avi m etr ic s o i l moisture is inp ut to the model, then so il
bulk d e n s i t y must a l s o be en te red .
A l i n e a r i n t e r p o l a t i o n subroutine
c r e a t e s a new d a t a s e t from t h e in pu t d at a so t h a t s o i l moisture co nt ent
and s o il temperature ar e s p e c i f i e d in one cm t h i c k l a y e r s f o r th e top
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24
50 cm of the soil p r o f i l e .
The remainder o f the s o il p r o f i l e is divided
in t o 10 cm t h i c k l a y e r s down t o a maximum depth of 3.5 m.
The model
has the c a p a b i l i t y of c a l c u l a t i n g th e emission from a sand, loam, o r
cl ay s o i l a t microwave f req uen ci es of 10.6 GHz (X-band), 4.0 GHz (Cband), and 1.4 GHz (L-band).
Soil d i e l e c t r i c co n sta n ts a r e mathemati­
c a l l y defined as a f un cti on of volumetric so il moisture co n t e n t f o r
each of the t h r e e freque nci es f o r each s o i l type.
Soil d i e l e c t r i c
c o ns ta nt s a t a frequency of 10.6 GHz do not vary with s o il type.
Such
q u a n t i t i e s as br ig h t n es s temperature (a measure of emitted thermal
microwave r a d i a t i o n ) f o r each la y e r of th e s o i l , t o t a l b ri g h t n es s
temperature a t t h e s o i l s u r f a c e , e m i s s i v i t y a t th e s o i l s u r f a c e , and
eq u i v a le n t incoherent soil moisture co nt ent are c a l c u l a t e d f o r ten
in c id e n t angles ranging from 0 t o 80 degrees and f o r ho riz ont al and
v e r t i c a l p o l a r i z a t i o n s a t each of th e t h r e e fr e q u e n c i e s .
Em issivity i s
c a l c u l a t e d by d iv id in g th e t o t a l b rig h tn es s temperature of t h e s o i l
volume by the so il temperature of the sur fac e la y e r .
The e q u i v a le n t
incoherent s o il moisture c o n t e n t (from now on r e f e r r e d to as EQSM) is
determined by summing the s o i l moisture content f o r each s o i l l a y e r ,
weighted by t h e percentage energy c o n t r i b u t i o n of t h a t l a y e r t o th e
t o t a l energy emitted a t th e s o i l s ur f ac e (Newton, 1977).
In r e a l i t y ,
EQSM is an es ti ma te o f the a v a i l a b l e water in some volume o f s o i l seen
by a radiometer.
From t h i s q u a n t i t y , p e n e t r a t i o n depth of th e microwave
sensor f o r a given frequency i s determined by matching th e c a l c u l a t e d
EQSM with the weighted average volumetric moisture co nt ent c a l c u l a t e d
from the a ct u al s o i l moisture d at a.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
25
For t h i s stu d y, volumetric s o i l moisture con te nt and s o il tempera­
t u r e simulated by th e water and heat balance model were input to the
r a d i a t i v e t r a n s f e r model.
a s o i l depth of 1.5 m.
Cal culations by the model were li m it ed to
Brightness temperature, e m i s s i v i t y , EQSM,
and p e n e t r a t i o n depth were determined a t a zero degree i n c id e n t angle
and f o r h o r iz o n t a l p o l a r i z a t i o n in o rd er to simul ate the response of
10.5 GHz and 1.4 GHz radiometers looking a t a smooth, bare s o i l .
Thus,
from each s e r i e s of simulated s o il moisture p r o f i l e s f o r the h y po th e ti­
cal loam-like s o i l , t h e r e corresponds a s e r i e s of simu latio ns to
determine how rad iometers would respond to these s o i l moisture condi­
tions.
Results
Soil moi sture p r o f i l e s for a number o f r a i n f a l l events were
simulated by a water and heat balance model (Van Bavel and H i l l e l , 1975,
1976).
Soil water co n t e n t was pr in te d f o r each o f the 28 la y e r s a t
2:00 p.m. f o r th e hy po th e tic a l loam-like s o i l .
Time s e r i e s p lo t s of
these s o il mo ist ur e p r o f i l e s ar e presented in Figs. 2 through 10 f o r
s e le c te d r a i n f a l l ev e n t s.
These graphs show t h a t wate r i n f i l t r a t e s to
g r e a t e r depths withi n the s o i l p r o f i l e due t o incre as ed r a i n f a l l amounts
and/or highe r i n i t i a l s o i l moisture c o n d i ti o n s .
Deeper p e r co la ti on of
water due t o l a r g e r r a i n f a l l amounts is e s p e c i a l l y noted in F igs. 3, 5,
7, and 9.
Each of t h e s e simu latio ns s t a r t e d with th e same i n i t i a l soil
moisture p r o f i l e .
Higher i n i t i a l moisture co nt en ts inc reased the wetting
f r o n t advance r a t e as noted by P h i l l i p (1957) f o r i d e n t i c a l amounts of
precipitation.
This i s e v id en t by comparing Figs. 3 and 4, Figs. 5 and
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
26
MOISTURE
CONTENT
{7 .
BY
VOLUME)
o
232
233
234
235
241
rn
o
FIG. 2. Simulated s o i l moisture p r o f i l e s produced by 1,27 cm
p r e c i p i t a t i o n on a hyp othetical loam-like s o il t h a t had previously
received a 2.54 cm r a i n . J u li a n day 232 r e p r e s e n t s the soil
moisture s t a t u s p r i o r to the r a i n f a l l event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
27
MOISTURE
CONTENT
IX
BY
VOLUME!
25
* 202
© 203
m
x 204
* 205
o 208
o
FIG. 3. Simulated s o i l moisture p r o f i l e s produced by 2.54 cm
p r e c i p i t a t i o n on a hypoth et ica l loam-like s o i l t h a t was i n i t i a l l y
dry. J u li a n day 202 r e p r e s e n t s the s o il moisture s t a t u s p r i o r to
the r a i n f a l l event.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
28
MOISTURE
O
5
10
CONTENT
15
20
(7.
25
BY
VOLUME)
30 '
35
40
•c
*
212
m
“0
o
Ui
o
FIG. 4. Simulated s o i l moisture p r o f i l e s produced by 2.54 cm
p r e c i p i t a t i o n on a hypoth et ica l loam-like s o i l t h a t had pr eviousl y
received a 2.54 cm r a i n . J u li a n day 212 re p r e s e n t s the so il
moisture s t a t u s p r i o r to th e r a i n f a l l event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
29
MOISTURE
CONTENT
17.
BT
VOLUME)
1— 4
o 137
* 198
a 201
s 206
n
o
FIG. 5. Simulated s o i l moisture p r o f i l e s produced by 5.08 cm
p r e c i p i t a t i o n on a hy po th e tic a l loam-like s o il t h a t was i n i t i a l l y
dry. J u l i a n day 196 re p r e s e n t s the s o i l moisture s t a t u s p r i o r to
the r a i n f a l l event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
30
M O I S T U R E C ON T E NT
o
m
"0
5
10
15
20
17. BY VOLUME]
25
30
35
X 214
* 219
x 223
O
y
235
o
FIG. 6. Simulated s o il moisture p r o f i l e s produced by 5.08 cm
p r e c i p i t a t i o n on a hyp ot h e tic a l loam-like s o il t h a t had previously
received a 5.08 cm r a i n . J u l i a n day 212 r e p r e s e n t s th e so il moisture
s t a t u s p r i o r t o the r a i n f a l l even t.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
31
MOISTURE
O
5
10
CONTENT
15
20
{'/.
25
BY
VOLUME!
30
35
40
o
nj
o
JZ
o
* 196
o 197
+ 199
a 200
co
o
2 202
x 206
a
o
o
.e
o
FIG. 7. Simulated s o i l moisture p r o f i l e s produced by 7.62 cm
p r e c i p i t a t i o n on a hypoth et ica l loam-like s o il t h a t was i n i t i a l l y
dry. Ju li a n day 196 r e p r e s e n t s the s o i l moisture s t a t u s p r i o r to
th e r a i n f a l l event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
32
MOISTURE
CONTENT
{'/.
BY
VOLUME)
212
m
O
■<>*
220
223
227
234
241
o
FIG. 8 . Simulated soil moisture p r o f i l e s produced by 7.62 cm
p r e c i p i t a t i o n on a hypothetical loa m-lik e s o i l t h a t had previously
received a 7.62 cm r a in . J u li a n day 212 r e p r e s e n t s the s o i l moisture
s t a t u s p r i o r t o the r a i n f a l l event.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
33
O
MOISTURE
5
10
CONTENT
15
20
(X
25
BY
VOLUME)
30
35
*
o
x
+
196
197
1.98
199
o
^
s
x
20 0
201
203
206
♦
211
«0
F I G . 9 . Simulated s o il moisture p r o f i l e s produced by 10.16 cm
p r e c i p i t a t i o n on a hypoth et ica l loam-like s o il t h a t was i n i t i a l l y
dry. Julia n day 196 r e p r e s e n t s t h e s o i l moisture s t a t u s p r i o r to
the r a i n f a l l event.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
34
MOISTURE
CONTENT
(X
BY
VOLUME)
o
o
ru
o
•c
o
X
a
■■
co
o
*
o
o
221
r 223
♦ 23Q
z 241
o
00
o
U>
a
■c
o
FIG. 10. Simulated s o i l moisture p r o f i l e s produced by 10.16 cm
p r e c i p i t a t i o n on a hy p o th e tic a l loam-like s o i l t h a t had previously
received a 5.08 cm r a i n . J u l i a n day 212 r e p r e s e n t s the so il
moisture s t a t u s p r i o r to the r a i n f a l l event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
35
6 (pp. 29 and 30) , Figs. 7 and 8 (pp. 31 and 32), and Figs. 9 and 10 (pp.
33 and 34).
Small r a i n f a l l events (Figs. 2 and 3, pp. 26 and 27) do not
add a p pr ec ia bl e q u a n t i t i e s of water to th e s o i l p r o f i l e ; t h u s , most o f
i t is l o s t by evapo ration as found by Gardner and Gardner (1969).
They a l s o s t a t e d t h a t more water is saved from evaporation loss due
to la r g e r a i n s because water moves deeper in t o the s o i l .
The thermal microwave emission from th e simulated s o i l moisture
p r o f i l e s was modeled by a r a d i a t i v e t r a n s f e r approach (Newton, 1977)
f o r f r equ enc ie s of 10.6 GHz (X-band) and 1.4 GHz (L-band).
Brightness
temperatures a t f ix e d i n t e r v a l s within th e hypoth et ica l soil p r o f i l e
were c a l c u l a t e d from simulated s o i l moisture and s o i l temperature condi­
t i o n s produced by r a i n f a l l amounts of 1.27 cm, 2.54 cm, 5.08 cm, and
7.62 cm.
The b ri g h t n e s s temperature produced by each so il la y er a t
both fre qu en ci es as c a l c u l a t e d by the model was converted t o percent of
t o t a l emitted energy and p l o t t e d as a time s e r i e s .
Results o f the 10.6
GHz and 1.4 GHz f r equ enc ie s are shown in Figs. 11 through 14.
The major­
i t y o f th e r a d i a t i o n emitted a t a frequency o f 10.6 GHz comes from a
depth of one to two cm. This has been documented by Newton (1977). Energy
emitted a t 10.6 GHz i s also shown to come from the su rf ac e la y e r of
s o i l over longe r periods of time f o r l a r g e r r a i n f a l l event s.
For the
1.27 cm r a i n (Fig. 11 A), the percentage o f t o t a l energy r a d i a t i n g from
the s u r f ac e cm of s o i l ret ur n ed t o i t s i n i t i a l s t a t e within two days
a f t e r th e r a i n ; whereas, f o r a 7.62 cm r a i n (Fig. 14A), seven days
elapsed before the i n i t i a l c o n di tio n was again reached.
The same
general tr e n d s a r e shown by L-band (1 .4 GHz frequency) f o r th e d i f f e r e n t
r a i n f a l l ev ent s.
As the s o i l p r o f i l e inc reased in moisture con tent due
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
36
EMITTED
ENERGY
{V.
OF
TGTfflJ
100
o-
(f»
X-BflNO
(B3 L-BflNO
232
233
234
235
241
O
tn
>c
j=
FIG. 11. Contribution of emitted microwave energy with depth in r e l a ­
ti o n to th e t o t a l emitt ed energy as c a l c u la te d by the r a d i a t i v e
t r a n s f e r model f o r X-band (A) and L-band (B) from 1.27 cm p r e c i p i t a t i o n
on a hypoth et ica l loa m- li ke s o i l t h a t had previously received a 2 .5 4 cm
r ai n .
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
37
EMITTED
ENERGY
V/.
OF
TOTAL)
100
o
(RJ X-BRND
W)
(B)
L-BflNO
212
214
D
<S!
FIG. 12. Contribution of emitted microwave energy with depth in r e l a ­
t i o n t o th e t o t a l emitted energy as c a l c u la te d by the r a d i a t i v e t r a n s f e r
model f o r X-band (A) and L-band (B) from 2.54 cm p r e c i p i t a t i o n on a
hypothetical loam-like s o i l t h a t had pr ev io us ly received a 2.54 cm
r ai n.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
38
EMITTED
ENERGY
(X
OF
T0TRL)
18)
L-BRND
FIG. 13. Contribution of emitted microwave energy with depth in r e l a ­
t i o n t o th e t o t a l emitted energy as c al cu la te d by th e r a d i a t i v e
t r a n s f e r model f o r X-band (A) and L-band (B) from 5.08 cm p r e c i p i t a t i o n
on a hy pothe tical loam-like s o i l t h a t had previ ou sl y received a 5.08 cm
r a in .
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
39
E M I T T E D ENERGY
to
20
30
HO
50
C /. OF TOTAL)
60
70
90
100
UT
(fl) X-BflND
0
2
CO
Q
(B) L-BflND
m
“0
217
218
220
n
cn
22.3
227
234
2.41
UT
>s
FIG. 14. Contri bution of emitted microwave energy with depth in r e l a ­
ti o n to the t o t a l emitted energy as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model f o r X-band (A) and L-band (B) from 7.62 cm p r e c i p i t a t i o n
on a hyp othetical loa m- li ke s o il t h a t had p re v io u s ly receive d a 7.62 cm
r ain .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm issio n .
40
to l a r g e r r a i n f a l l s , th e c o n t r i b u t i o n o f energy from th e upper p or ti o ns
of the s o i l p r o f i l e was s u st ai n e d f o r longer periods of time.
The most
noteworthy ob se rva ti on made while examining th e s e graphs was t h a t th e
emitted r a d i a t i o n a t 1.4 GHz frequency came from deeper la y e rs than t h a t
sensed by X-band.
More than 99 per ce nt of th e t o t a l emitted energy
r ad ia te d from wi th in th e top 50 cm of th e s o i l p r o f i l e .
I t i s without
doubt t h a t t h i s longe r wavelength is more s e n s i t i v e to s o il moisture
and has the c a p a b i l i t y of pe ne t r a ti n g to deeper depths (Newton, 1977;
Schmugge e t a l . , 1976).
Pene tra tio n depths f o r the 10.6 GHz and 1.4 GHz frequencies as
c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model were superimposed on the
time s e r i e s s o i l moisture p r o f i l e p l o t s (Figs. 15 through 19) t h a t
were presented e a r l i e r f o r s e l e c t e d r a i n f a l l ev ent s.
X-band p e n e t r a t i o n
depth is in d ic ate d by th e s h o r t dashed l i n e while L-band depth of pene­
t r a t i o n i s rep re se nt ed by th e longer dashed l i n e .
These f i g u r e s c l e a r l y
i n d i ca te th e dynamic response o f microwave radiometers to n e a r - s u r f a c e
s o il moisture.
As the s o i l d r i e s , p e n e t r a ti o n depth in c re a s e s .
For
t h i s hypothetical loa m-lik e s o i l , p e n e t r a ti o n depths ranged between
0.5 cm and 2.3 cm f o r X-band with a maximum depth of approximately 3 cm
from very dry s o il c o n d i t i o n s ; L-band p e n e t r a ti o n depths v ar ie d from
5 cm to 25 cm.
A maximum p e n e t r a t i o n depth of 39 cm (Fig. 18) was
c al c u la te d f o r the L-band radiometer from the same dry so il c on di ti o ns
t h a t produced a 3 cm depth of p e n e t r a t i o n f o r X-band.
P en et ra tio n
depths c a l c u l a t e d f o r th e two freque nci es ar e deeper than es ti m at es of
p e n et r at io n made from f i e l d experiments conducted by ot h e r i n v e s t i g a ­
tors.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
O
a
m
“0
MOISTURE
5
10
CONTENT
15
20
(X
25
BT
VOLUME)
30
35
40
e 213
x 214
+ 215
* 224
x 230
-
X-SflNO
L-BRNO
iC
cn
FIG. 15. P en et ra ti o n depths ca l c u la te d by th e r a d i a t i v e t r a n s f e r
model f o r X-band ( s h o r t dashes) and L-band (long dashes) from
simulated s o i l moisture p r o f i l e s produced by a 2.5 4 cm ra in on a
hyp othetical loam-like s o i l t h a t had previously received 2.5 4 cm
precipitation.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
42
MOISTURE
CONTEN T
(7.
BT
VOLUME]
o
in
in
Qo
1— 4
r~
21.2
214
215
c
o
x±
219
223
228
235
241
X-BflNO
L - 8 fiND
>c
in
in
o
FIG. 16. P en et rat io n depths c a l c u l a t e d ' b y the r a d i a t i v e t r a n s f e r
model for X-band ( s h o r t dashes) and L-band (long dashes) from
simulated s o il moisture p r o f i l e s produced by a 5.08 cm rain on a
hypothetical loam-like s o il t h a t had previously receive d 5.08 cm
precipitation.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
43
MOISTURE
5
10
CONTENT
15
20
IZ.
BT
25
VOLUME)
30
35
5Qo
2"
m
T<>
*
±<>t! -•
220
« 223
y 227
X-BflNQ
1-BflNO
cn
£&s^sass?j?jss»
S K
M
. ! 0" - ’ 1*
" "
that
S
- " a
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
40
44
o
MOISTURE
5
10
CONTENT
15
20
(7. BY VOLUME)
25
30
35
196
197
198
199
20 0
201
2 03
2.06
n
X-BflNO
L - 8 ANQ
•c
FIG. 18. P en et ra tio n depths c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r
model f o r X-band ( s h o r t dashes) and L-band (long dashes) from
simulated s o i l moisture p r o f i l e s produced by a 10.16 cm r a i n on a
hy poth etica l loam-like s o i l t h a t was i n i t i a l l y dry.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
45
MOISTURE
5
10
CO N T E N T
15
20
{'/.
25
BT
VQLU'ME)
30
35
e *Q Q Q o
0
Qo
OJ
216
217
218
219
221
223
230
241
n
X-BflNO
L-8RN0
o ‘
FIG. 19. P en et ra tio n depths c a l c u la te d by th e r a d i a t i v e t r a n s f e r
model for X-band ( s h o r t dashes) and L-band (long dashes) from
simulated s o i l moisture p r o f i l e s produced by a 10.16 cm ra in on a
hypothetical loam-like s o il t h a t had previ ous ly receive d 5.08 cm
precipitation.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
46
Since i t has been e s t a b l i s h e d t h a t L-band is more s e n s i t i v e to s o i l
moisture cond it ion s and t h a t i t has the ca p a ci ty of sensing t h i c k e r
portions of the n e a r - s u r f a c e s o i l p r o f i l e , i t i s necessary to determine
what s o i l moisture information i t provides.
To do t h i s , L-band EQSM
as c a l c u l a t e d by t h e r a d i a t i v e t r a n s f e r model was compared t o the t o t a l
amount of water s to r e d in t h e top 15 cm, top 21 cm, and top 30 cm of
th e hy poth etica l loa m-l ik e s o il p r o f i l e over a period o f 24 days
following a 10.16 cm r a i n f a l l event (see Figs. 20, 21, and 22, res pec ­
tively).
To make the comparison somewhat e a s i e r , the axis repres ent ing
s o il water co nt en t was allowed to f l o a t f o r th e se t h r e e p lo ts so t h a t
the amount of water in th e p r o f i l e depth in question could be s e t equal
to the EQSM on the l a s t day of th e simulation perio d.
The amount of
water in the top 15 cm and in th e top 21 cm of the s o i l p r o f i l e was
nea rly equal to L-band EQSM during the e n t i r e s im ul ati on period.
How­
eve r, since EQSM and water co n te nt on the day of r a in were almost the
same f o r th e 21 cm p r o f i l e , i t was decided t h a t L-band repres ent ed the
amount of water in th e top 21 cm of s oi l b e t t e r than in the top 15 cm.
L-band EQSM was not r e l a t e d very well to the s o i l water content in the
top 30 cm o f th e s o i l p r o f i l e .
Since EQSM is not a measurable q u a n t i t y , s o il water content should
have been compared with L-band e m i s s i v i t y .
Emissivity can be c a l c u ­
l a t e d from measured b r i g h t n e s s temperature and s o i l s u r f a c e temperature.
However, EQSM was s e l e c t e d because a time p l o t of t h i s c a l c u l a t e d v a r i ­
able showed t h e same general t r e n d s as did a time p l o t of water content
in the upper p o r ti o n o f th e s o i l p r o f i l e (Figs. 20 through 22).
n a t e l y , e m is s i v it y and EQSM are r e l a t e d as shown in Fig. 23.
Fortu­
For
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
Reproduced with permission
cn
o
CD
ID
o SOIL WATER CONTENT
x L-BflND EQSM
f RflINFRLL
cn
o
cn
cn
CONTENT
m
WATER
O
prohibited without perm ission.
SOIL
of the copyright owner. Further reproduction
(CM)
in
m
o
1
3
5
7
9
11
TIME
13
15
(DRYS)
17
19
21
23
25
FIG. 20. R e l a t i o n between L-band EQSM and s o i l w at er c o n t e n t in t h e to p 15 cm o f t h e h y p o t h e t i c a l
l o a m - li k e s o i l p r o f i l e .
-p»
^-4
Reproduced with permission
o
LO
O
CONTENT
CD
Q
in
ro
f RAINFALL
WRTER
CO
o SOIL WATER CONTENT
x L-0ANO EQSM
prohibited without p erm ission .
SOIL
of the copyright owner. Further reproduction
(CM)
in
o
r\j
23
TIME
25
(DOTS)
FIG. 21. R e l a t i o n between L-band EQSM and s o i l w a t e r c o n t e n t in th e top 21 cm o f th e h y p o t h e t i c a l
loam-like so il p r o f i l e .
-p »
CO
Reproduced with permission
CM
of the copyright owner. Further reproduction
O
O
Q
u>
OQ
cn
SOIL WATER CONTENT
L-BAND EQSM
RAINFALL
cn
o
CO
CC
LU
CC
CO
in
prohibited without p erm ission.
o
*—i
1
3
5
7
9
11
TIME
13
15
(DRYS)
17
19
21
23
25
FIG. 22. R e l a t i o n between L-band EQSM and s o i l w at er c o n t e n t in th e to p 30 cm o f t h e h y p o t h e t i c a l
loam-like so il p r o f il e .
-p*
<43
50
cn
o
■
(L-BAND)
t
3
j»
CO
J£Q
9
o
SB
EMISSIVITY
o
ID
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0
in
o
3*
°0
10
15
EQ S M
20
25
30
35
( X BY V O L U M E )
40
45
50
FIG. 23. Re la ti o ns hi p between L-band e m i s s i v i t y and L-band EQSM as
c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
51
i l l u s t r a t i o n purposes, comparison pl o ts between EQSM and amount of
water in th e s o i l p r o f i l e will s u f f i c e .
E f f ec ts of r a i n f a l l amount on comparisons between EQSM and water
con te nt in th e top 21 cm of the s o il p r o f i l e versus time are shown in
Figs. 24 through 32.
For small r a i n f a l l amounts, as shown in Figs.
24, 25, and 25, L-band does not repr es ent the s o i l water con tent in the
top 21 cm s o i l la y e r very well on the day of r a i n .
r e l a t i o n s h i p i s good.
At o th e r times, the
A very good comparison is shown in Fig. 27 f o r a
5.08 cm r a i n on a dry s o i l p r o f i l e .
For the l a r g e r events, L-band
appears to un derestimate th e amount of water in t h e 21 cm p r o f i l e f o r a
period of several days a f t e r t h e r a in (Figs. 28 through 32).
However,
s i m i l a r tr en d s e x i s t between th e two v a r i a b l e s , and th e maximum
d i f f e r e n c e i s on th e orde r of 0.4 cm of water.
Therefore, i t was con­
cluded t h a t the L-band sensor adequately r ep r es en t ed the so il moisture
s t a t u s in the top 21 cm of th e s o i l p r o f i l e .
I t has been shown t h a t L-band provides an estimate of th e so il
moisture in the su rf ac e 21 cm of th e s o il p r o f i l e .
comparisons with EQSM.
This was based on
As previously pointed o ut , EQSM is not a
measurable q u a n t i t y , n e i t h e r i s e m i s s i v i t y , but i t can be ca l c u la te d
from measured parameters.
Thus, L-band e m is s i v it y and so il water con­
t e n t in the top 21 cm o f th e hypothetical loam-like s o i l were p lo t te d
f o r s e l e c t e d r a i n f a l l events (Fig. 33).
This r e l a t i o n s h i p in d i c a t e s
t h a t the wa ter co nt ent in the top 21 cm o f th e s o i l p r o f i l e can be
p re d ic te d from L-band e m i s s i v i t y .
A somewhat i n s e n s i t i v e region
developed below a soil water co nt ent of 4.0 cm of water.
This water
content in th e 21 cm s o i l p r o f i l e corresponds to a mean volumetric
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
52
SOIL WATER CONTENT
L-BANO EQSM
RAINFALL
toi—
u
to
LU
AJO
*-•(I
202
to
20 6
TIME
210
( DATS)
FIG. 24. Comparison between L-band EQSM and s o il water con tent in
the top 21 cm of the hy po the tica l loam-like s o il p r o f i l e f o r a 2 .5 4
cm ra in on an i n i t i a l l y dry p r o f i l e .
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
53
■1 05
- OD
Q SOIL WATER CONTENT
x L-8AN0 EQSM
a*
SOIL
WATER
CONTENT
(CM)
f RfllNFRLL
212
216
220
TIME
( DAT S)
228
232
FIG. 25. Comparison between L-band EQSM and s o i l water c on t en t in
the top 21 cm of the h y p o th e tic a l loa m-like s o i l p r o f i l e f o r a 2 .5 4
cm r a i n t h a t followed a previous 2.54 cm r a i n event.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
54
0 SOIL HATER CONTENT
x L-BflNO EQSM
f RAINFALL
ME
U
LU
U
to
UJ
232
236
TIME
( DRYS)
FIG. 26. Comparison between L-band EQSM and s o il water content in
the top 21 cm o f the hy pot hetical loam-like s o i l p r o f i l e f o r a 1.27
cm r a in t h a t followed a previous 2.54 cm r a i n event.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
55
(CM)
SOIL WATER CONTENT
L-8AN0 EQSM
RAINFALL
a*
CONTENT
iP
>-
WATER
120
SOIL
cn
o
LU
196
200
TIME
20»*
( DAYS)
208
212
FIG. 27. Comparison between L-band EQSM and s o il water content in
the top 21 cm o f th e hypoth et ica l loam-like s o i l p r o f i l e f o r a 5.08
cm r a i n on an i n i t i a l l y dry p r o f i l e .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
Reproduced
with permission
CD
O
of the copyright owner. Further reproduction
© SOIL WATER CONTENT
x L-BAND EQSM
f RAINFALL
ID
to
CD
CD
o
ID
CM
CM
Ct
(0 2
o
prohibited without p erm ission .
ID
O
212
O
216
220
TIME
228
( DAYS)
232
236
2 M0
FI 6 . 28. Comparison between L-band EQSM and s o i l w a te r c o n t e n t in th e top 21 cm o f t h e h y p o t h e t i c a l
l o a m - l i k e s o i l p r o f i l e f o r a 5.08 cm r a i n t h a t followed a p re v io u s 5. 0 8 cm r a i n e v e n t .
tn
cn
57
(CM)
a SOIL WATER CONTENT
x L-BANO EQSM
f RAINFALL
CONTENT
'" “.Q
WATER
CD
SOIL
UJ
196
O
200
204
TIME
( DATS)
208
212
FIG. 29. Comparison between L-band EQSM and s o il water content
in the top 21 cm of th e hy po the tica l loam-like s oi l p r o f i l e f o r
a 7.52 cm r a i n on an i n i t i a l l y dry p r o f i l e .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
Reproduced
with permission
in
CJ>
3*
in
co
f RAINFALL
co
CONTENT
(CM)
© SOIL WATER CONTENT
x L-0HNO EQSM
in
CD
<M
WATER
ru
3
UJ =
prohibited without perm ission.
SOIL
of the copyright owner. Further reproduction
O
3*
o
in
o —
21 2
o
216
220
TIME
226
(DOTS)
232
236
FIG. 30. Comparison between L-band EQSM and s o i l w a te r c o n t e n t in th e top 21 cm o f th e h y p o t h e t i c a l
l o a m - l i k e s o i l p r o f i l e f o r a 7.62 cm r a i n t h a t fo llowed a p r e v io u s 7.6 2 cm r a i n e v e n t .
cn
00
59
Q SOIL WATER CONTENT
x L-BRND EQSM
- co
f RAINFALL
o
~IP
UJ
co
o
UJ
cuo
to
196
200
2 0 il
TIME
( DATS)
208
FIG. 31. Comparison between L-band EQSM and so il water co nt ent
in the top 21 cm of th e hy po the tica l loam-like soil p r o f i l e f o r
a 10.16 cm r a in on an i n i t i a l l y dry p r o f i l e .
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
Reproduced
with permission
in
a*
O)
o
CONTENT
tCM)
RAINFALL
ro
CO
CD
in
<u
WRTER
■>Jo
<u
S»«LU
prohibited without perm ission.
SOIL
of the copyright owner. Further reproduction
SOIL WATER CONTENT
L-BAND EQSM
O
in
D
212
o
216
220
228
TIME
( DAYS)
2S2
236
FIG. 32. Comparison between L-band EQSM and s o i l w ate r c o n t e n t in t h e to p 21 cm of t h e h y p o t h e t i c a l
lo a m - li k e s o i l p r o f i l e f o r a 10.16 cm r a i n t h a t f o ll ow ed a p r e v io u s 5.08 cm r a i n e v e n t .
cr>
o
61
o
05
05
f—
UJ
f—
z
OJ
o
0.3
0.5
0.6
0.7
0.8
L-BflND E M I S S I V I T Y
0.9
1. 0
FIG. 33. R e la ti on sh ip between so il water c o nt en t in the top 21 cm
of the h y p ot h e tic a l loam-like soil p r o f i l e and L-band e m is s i v it y as
c a l c u la te d by the r a d i a t i v e t r a n s f e r model f o r s e l e c t e d r a i n f a l l
events.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
62
moisture cont ent of 19 p erc en t.
From the p res su re p o t e n t i a l versus
volumetric moisture co nt en t r e l a t i o n s h i p f o r t h i s hy pothe tical s o i l , a
moisture cont ent of 19 p e r c e n t corresponds to a pr es su re p o t e n t i a l of
-15 m of water column (1 .5 b a r s ) .
Thus, the beginning of t h i s region
i s in the lower p a rt of th e a v a i l a b l e s o il water range.
Available water in a s o i l has been defined as the amount of water
used or removed from th e s o i l f o r th e support of p l a n t l i f e .
I t is
estimated by th e d i f f e r e n c e between water contents a t f i e l d ca p a ci t y and
the permanent w i lt in g p o in t ( P e t e r s , 1965).
Using th e c l a s s i c a l values
of 1/3 bar p r e s s u r e p o t e n t i a l t o es ti ma te f i e l d ca p a ci t y and 15 bars to
estimate permanent w i l t i n g f o r a medium te x tu r e d s o i l , th e s o i l moisture
contents rep re se nt in g th e upper and lower l i m i t s of a v a i l a b l e water are
25.4 and 12.2 p e r c e n t , r e s p e c t i v e l y , f o r t h i s hy pothetical loam-like
soil.
The upper and lower l i m i t s of a v a i l a b l e water are al so r e p r e ­
sented by 5.33 and 2.56 cm of wa ter, r e s p e c t i v e l y , in th e top 21 cm of
the s oi l p r o f i l e .
The main p a r t of t h e curve was well de fin ed over a range o f water
contents from n e a r - s a t u r a t i o n down to a water co n te nt of 4.0 cm a t
which the d i s c o n t i n u i t y occurred.
A s a t u r a t e d co ndi tio n f o r th e top
21 cm of t h i s h ypo the tica l s o i l is rep re se nt ed by 8.21 cm of water.
When the simulated r e s u l t s f o r a l l r a i n f a l l events were p l o t t e d ,
the r e l a t i o n s h i p between s o i l water content and L-band e m is si v it y
produced o ut ly in g points ( r e p r e s e n te d by an X) as shown in Fig. 34.
These points occurred on th e day o f r a i n f o r simul ati on runs Cl, C2,
C3, D3, El, E2, G2, and II and were the r e s u l t of small r a i n f a l l
amounts and/or r a i n on dry s o i l (see Table 2, p. 22) which caused a
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
63
at
co
CJ'
“ ■CO
L
U
h:z :
<D
R = 0.
CJLO
QC
UJ
I—
CE31
2
'(f)
O
CD
cu
x INVERTED PROFILE
0 REGULAR PROFILE
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
L-BAND EM ISSIVITY
FIG. 34. R e la ti on sh ip between s o i l wa ter cont ent in th e top 21 cm
of the hy pot he tic al loam-like s o il p r o f i l e and L-band e m i s s i v i t y as
c a l c u l a t e d by the r a d i a t i v e t r a n s f e r model f o r a l l simulated r a i n f a l l
even ts.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
64
wet la yer of s o il to form over dry s o i l in the upper p o r ti on of th e s o il
profile.
29.
This co n d i ti o n was shown in Figs. 2 through 5 (pp. 26 through
Newton (1977) c l a s s i f i e d t h i s s o i l moisture condition as an i n ­
verted p r o f i l e .
He s t a t e d t h a t an inv ert ed p r o f i l e could be determined
by comparing the 10.6 GHz es ti ma te of EQSM to the 1.4 GHz e s t i m a t e of
EQSM.
I f X-band EQSM is l a r g e r than L-band EQSM, then the s u r f a c e i s
w et te r than the immediate su bsurface.
I t so happens t h a t X-band EQSM
was l a r g e r than L-band EQSM f o r each of the above simulation runs.
Conditions t h a t e x i s t e d on th e day of r a i n f a l l are l i s t e d in Table 3
f o r each of th e r a i n ev ent s.
X-band EQSM was also l a r g e r than L-band
EQSM on the day of rai n f o r sim ulation runs Gl, Q2, R2, and 52; however,
t h i s d i f f e r e n c e was considered i n s i g n i f i c a n t .
The point re p r e s e n t e d by
simulation 12 , loc at ed on th e main curve, was s e le c te d as the p iv ot
p o s it i o n t o connect the in ve rte d p r o f i l e points to the r e s t o f th e
simulated r e s u l t s .
X-band EQSM was 0.52 percent l a r g e r than L-band EQSM
for t h i s p a r t i c u l a r po in t .
Instead of using EQSM f o r both f re qu enc ie s
to i d e n t i f y th e s e in v e rt ed p r o f i l e s , i t was found t h a t the change in
L-band e m i s s i v i t y ( e m i s s i v i t y the day a f t e r th e r a i n minus e m i s s i v i t y
the day of r a i n ) accomplished th e same r e s u l t .
Blanchard (1979) and
Blanchard and Bausch (1979) hypothesized t h a t the r a t e of change in Xband and L-band measurements could be used to provide a measure of the
drying r a t e of s o i l .
The change in X-band e m is s i v it y could a l s o be
used t o c l a s s i f y in v e rt ed p r o f i l e s .
However, as the s o i l s u r f a c e is
roughened, the s e n s i t i v i t y to s o i l moisture by X-band i s dec re ase d;
whereas, s u r f ac e roughness only has minimal e f f e c t s on L-band measure­
ments (Newton, 1977).
The L-band change in e m is s i v it y f o r p o in t 12
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
65
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66
was 0.18640.
Changes in L-band em is si v it y f o r s im ul at io n runs Cl, C2,
C3, D3, El, E2, and G2 were g r e a t e r than t h i s value as shown in Table
3 (p. 65).
Thus, in v ert ed s o il moisture p r o f i l e s caused by small
r a i n f a l l events can be c l a s s i f i e d i f the change in L-band e m is si v it y
is g r e a t e r than 0.18.
To obtain an idea how s o i l type would a f f e c t the r e l a t i o n s h i p
between s o il water co nt en t in the top 21 cm o f t h e s o il p r o f i l e and Lband e m i s s i v i t y , t h e two t h e o r e t i c a l models were used t o simulate
conditions for s a n d - l i k e and c l a y - l i k e s o i l s .
is shown in Fig. 35.
This s o i l t e x t u r e e f f e c t
The r e l a t i o n s h i p s f o r t h e h ypo the tica l s an d -li k e
and c l a y - l i k e s o i l s were developed by the same procedures used to
develop the r e l a t i o n s h i p f o r the loam-like s o i l .
Appropriate constants
and c h a r a c t e r i s t i c s d es cr ib in g the s o i l s were used in the t h e o r e t i c a l
simulation models.
These r e l a t i o n s h i p s f o r s a n d - l i k e and c l a y - l i k e s o il
are only approximate s in ce only two sim ul ati ons were run f o r each s o i l
type.
With th e l i m i t e d simulation ru ns , c h a r a c t e r i s t i c s describing
inverted p r o f i l e s could not be developed.
Considerable d i f f e r e n c e e x i s t s in t h i s r e l a t i o n s h i p f o r the t h r e e
major s o i l type s.
However, t h i s d i f f e r e n c e may not be as d r a s t i c as i t
f i r s t appears with an o per at ion al s a t e l l i t e .
Due to the v a r i a b i l i t y in
soil type over l a r g e a r e a s , i t is speculated t h a t the i n t e g r a t e d average
antenna br ig ht n es s temperature measured by a microwave radiometer f o r a
cell s i z e t h a t included several s o i l types would approximate the
antenna b r ig ht n es s temperature measured f o r a loam s o i l .
This may be
possible provided t h e optimum r e s o l u t i o n c e l l s i z e i s determined f o r
a radiometer.
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67
o
0)
00
UJ
fZ
0c
LU
F~
c r 3*
2
-J
'“ 'cn
O
C
O
CLftT
© LOAM
« SAND
EJ
o <—
0.3
0.5
0.7
0.8
0.9
1. 0
L - B f l N D 6E M I S S I V I T f
FIG. 35. E ff ec t of s o il t e x t u r e on the r e l a t i o n s h i p between s o i l
water co n t e n t in the top 21 cm of the se hy pot he tic al s o i l s and Lband e m i s s i v i t y as ca l c u la te d by the r a d i a t i v e t r a n s f e r model.
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68
An i n d i c a t i o n o f th e drying r a t e f o r th e hypothetical loam-like
s o i l was determined by p l o t t i n g X-band and L-band e m i s s i v i t i e s as
ca l c u la te d by the r a d i a t i v e t r a n s f e r model versus time.
Figs. 36
through 44 show th e e m is s i v it y - t im e r e l a t i o n s h i p s f o r s e l e c t e d r a i n f a l l
events.
All p l o t s show a dec re ase in e m i s s i v i t y a f t e r the r a i n f a l l
event followed by an in c r e a s e in e m i s s i v i t y on t h e day a f t e r r a i n .
In
g en er a l, th e change in e m i s s i v i t y during the drying cycle was g r e a t e r
th e f i r s t day a f t e r p r e c i p i t a t i o n than f o r any o th e r two consecutive
days.
Small r a i n f a l l events added very l i t t l e water to the s o i l p r o f i l e
(Figs. 2 through 4, pp. 26 through 28); t h u s , th e em is si v it y on the day
a f t e r rain was f a i r l y high and ne ar ly equal t o th e e m is si v ity p r i o r to
the rain as shown in Figs. 36, 37, and 38.
For l a r g e r r a i n f a l l events
two or more days elapsed a f t e r th e r a i n before th e em is si v it y s t a r t e d
to level o f f depending on whether th e s o i l p r o f i l e was dry or moderately
wet p r io r to th e event.
Since th e e m i s s i v i t y - t i m e r e l a t i o n s h i p s varied
considerably with r a i n f a l l amount, i t was hypothesized t h a t th e change
in e m is s i v it y a f t e r t h e day of r a i n should r e l a t e to the amount of
water added t o the s o i l p r o f i l e below t h e 21 cm s o i l depth.
Water
added to th e 21 cm to 150 cm l a y e r of th e s o i l p r o f i l e was determined
by taking the d i f f e r e n c e between th e maximum amount of water in t h a t
p o rt i o n of t h e p r o f i l e a f t e r t h e r a i n event and t h e amount of water
in the same p o rt i o n of t h e p r o f i l e befor e th e r a i n .
In most ca s es , the
maximum amount of wa ter in t h i s lower l a y e r o f th e s o i l p r o f i l e occurred
the day a f t e r th e r a i n while the minimum amount occurred th e day p r i o r
to th e r a in .
Exceptions to t h i s were sim u la ti o ns with r a i n f a l l amounts
of 1.27 cm and 2.54 cm.
Less than 0.5 cm of wa ter was added to the
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69
o
Ia J q
X-8RN0 EMIS
L-BRND EMIS
RAINFALL
206
TIME
210
( DATS)
FIG. 36. X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model versus time from a 2.54 cm ra in on the hypoth et ica l
loam-like s o i l t h a t was i n i t i a l l y dry.
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70
o
01
'■
• (■
1-0
>
l-H
UJo
X X- 8 ANQ EMIS
0 L-BflND EMIS
f RAINFALL
216
220
TIME
( DATS)
228
232
FIG. 37. X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model versus time from a 2.54 cm rai n on the hypothetical
loam-like s o i l t h a t had pr eviously received 2.54 cm o f p r e c i p i t a t i o n .
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71
o
*-o
>
x X-BflNO EMIS
0 L-BflNO EMIS
f RAINFALL
in
236
TIME
CDflTS)
FIG. 38. X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by th e r a d i a t i v e
t r a n s f e r model versus time from a 1.27 cm r a i n on the hyp othe tical
loam-like so il t h a t had pr ev iou sl y received 2 .5 4 cm of p r e c i p i t a t i o n .
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72
o
x X-BflNO EMIS
o L-BHND EMIS
f RAINFALL
196
200
204
T I ME
( DAT S)
208
FIG. 39. X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model versus time from a 5.08 cm ra in on the hypothetical
loam-like s o i l t h a t was i n i t i a l l y dry.
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Reproduced with permission
o
of the copyright owner. Further reproduction
O)
o
»r
prohibited without p erm ission .
<0
o
X-BflNQ EMIS
L-BflND EMIS
RflINFHLL
in
^12
216
220
TIME
228
(DATS)
232
236
FIG. 40. X-band and L-band emissivities as calculated by the radiative transfer model versus time from a
5.08 cm rain on the hypothetical loam-like soil that had previously received 5.08 cm of precipitation.
CO
74
o
X-BRNO EMIS
a L-BRND EMIS
f RRINFRLL
X
196
200
204
TIME
( DATS)
208
212
FIG. 41. X-band and L-band e m i s s i v i t i e s as c a l c u la te d by the r a d i a t i v e
t r a n s f e r model versus time from a 7.62 cm r a in on t h e hypothetical
loam-like s o i l t h a t was i n i t i a l l y dry.
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Reproduced with permission
o
of the copyright owner. Further reproduction
CD '
» t r
CO
CO
prohibited without p erm ission.
t£>
O
X-BAND EMIS
o L-BAND EMIS
f RAINFALL
X
21 6
220
TIME
228
(DATS)
232
236
FIG. 42. X-band and L-band emissivities as calculated by the radiative transfer model versus time from a
7.62 cm rain on the hypothetical loam-like soil profile that had previously received 7.62 cm of precipita­
tion.
76
o
O) '
>
2^ .
UJq
x X-BflNO E M I S
a L-BflNO E M I S
t RAINFALL
196
200
204
TIME
( DATS)
208
212
FIG. 43. X-band and L-band e m i s s i v i t i e s as c a l c u l a t e d by the r a d i a t i v e
t r a n s f e r model versus time from a 10.16 cm ra in on the hypothetical
loam-like s o il t h a t was i n i t i a l l y dry.
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
Reproduced with permission
o
of the copyright owner. Further reproduction
O)
o
CO
<n
#—I
UJo
prohibited without p erm ission.
o
X-BfiNO E M I S
L-BflNO E M I S
Rfl INFflLL
in
216
220
2 24
TIME
228
( DAYS)
232
236
FIG. 44. X-band and L-band emissivities as calculated by the radiative transfer model versus time from a
10.16 cm rain on the hypothetical loam-like soil that had previously received 5.08 cm of precipitation.
78
lower l a y e r of the s o i l p r o f i l e from th e se eve nt s.
The change in
e m i s s i v i t y one day a f t e r th e ra in ( e m i s s i v it y th e day a f t e r rain minus
the e m i s s i v i t y th e day o f ra in ) was c a l c u l a t e d f o r a l l th e simulated
r a i n f a l l events a t both fr equencies and p l o t t e d with the corresponding
amount of water added to th e lower po rtion of th e s o i l p r o f i l e as shown
in Fig. 45.
As s t a t e d above, very l i t t l e wate r was added t o th e s o i l
p r o f i l e from small r a i n s .
Consequently, th e changes in e m is s i v it y f o r
X-band and L-band were la r g e and near ly i d e n t i c a l .
Figs. 36 through 38 (pp. 69 through 71).
This was shown in
As r a i n f a l l amounts incre ase d,
the s u r fa ce d r ie d slower, and t h e change in X-band e m is s i v it y decreased.
More water was a l s o added to deeper po rtions of the s o i l p r o f i l e ;
t h e r e f o r e , L-band changed much slower.
through 44 (pp. 72 through 77).
This was al so shown in Figs. 39
Thus, a simple r a t i o of th e change in
e m i s s i v i t y f o r th e se two bands (change in X-band e m i s s i v i t y divided by
change in L-band e m i s s i v i t y ) appears to adequately r e p r e s e n t the amount
o f water added t o th e lower po rti o n of the s o i l p r o f i l e r e g a r d l e s s of
r a i n f a l l amount (see Fig. 46).
The s c a t t e r e d p oin ts d epi cte d by the
indi vidu al bands ar e not as prominent when the r a t i o of th e two bands
is used.
Due t o the slower drying r a t e of t h i s h y p o th e ti c a l s o i l following
l a r g e r r a i n f a l l s , r e s u l t s determined f o r a two day change in e m is s i v it y
( e m i s s i v i t y two days a f t e r th e r a i n minus e m i s s i v i t y the day of the
ra in ) were p l o t t e d in Fig. 47 f o r th e i n di vi d ua l bands.
r e l a t i o n s h i p was hard to d e t e c t due t o th e s c a t t e r .
A definite
However, both bands
showed t h e same general t r e n d ; th e r a t i o o f t h e two bands c l e a r l y
showed t h i s tr en d (Fig. 48).
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
79
LUO)
h—4
u_
o
cc
Q l CO
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CO
rLl
o
X
o
X
t—i CO
h—
CC
Cl
CL
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UJ
2
a
X
X
03*
0
0
X
0
2
o
w <o
a
LU
a
Cl
a : ai
*
X
ac
LU
1—
cc
2-
X-BRND
X
{ L-8RN0
♦
INVERTED PROFILE
-w*—*-
0.02
0.06
0.10
O. m
0.18
0.22
0.26
0.30
CHANGE I N E M I S S I V I T Y
FIG. 45. R e la ti o ns hi p between amount of water added to the hypothetical
loam-like s o i l p r o f i l e (21 to 150 cm depth) and the change in e m i s s i v i t y
one day a f t e r the r a i n f o r X-band and L-band.
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80
LU
LU
0.5
0.6
0.7
0.8
0.9
( D E L T A E M I S X J / ( DE L T A E M I S L )
1. 0
l.i
FIG. 46. Re l at i o n sh i p between amount of water added t o the hypothetical
loam-like s o i l p r o f i l e (21 t o 150 cm depth) and the r a t i o of X-band and
L-band change in e m i s s i v i t i e s one day a f t e r th e r a i n .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
81
LU O)
U_
o
cn
u_
arm
LU
o
Q
LU
x X-BflNO
a L - 8A N 0
LU
%*
-39»--0.02
0.06
0 . 10
0 . 14
0.18
0.22
CHANGE I N E M I S S I V I T Y
0.36
0.30
FIG. 47. R el ati ons hi p between amount of water added to th e hyp othetical
loam-like s o i l p r o f i l e (21 to 150 cm depth) andc ha nge in e m i s s i v i t y
two days a f t e r the r a i n f o r X-band and L-band.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
82
a. co
u_
= 0.8775
UJ
0. 6
0.7
0.8
0.9
1.0
( D E L T A E M I S X ) / ( DELTA E M I S L )
FIG. 48. R el at i o n sh i p between amount of water added t o th e hypoth et ica l
loam-like s o i l p r o f i l e (21 t o 150 cm depth) and th e r a t i o of X-band and
L-band change in e m i s s i v i t i e s two days a f t e r the r a i n .
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83
The Model
I t i s e v i d e n t from the above r e s u l t s t h a t microwave measurements
must be determined every day in o rd er to p r e d i c t s o i l water co nt ent with
any degree of accuracy.
The r ap id change in e m i s s i v i t y a f t e r small
r a i n s c l e a r l y i n d i c a t e s th e need f o r d a i l y measurements as does the
r e l a t i o n s h i p s developed t o e s ti m at e the amount of water added to the
lower p o r ti on o f t h e s o i l p r o f i l e .
The average d i f f e r e n c e between pre­
d ic te d valu es o f water added t o t h e lower p r o f i l e from th e b e s t f i t
polynomial and observed values f o r the two day change in e m is s i v it y was
0.8544 cm as opposed to 0.3416 cm f o r the one day change.
Also, i f an
ev er y- o th er -d ay measurement scheme was used as might be po s si b le with
la rg e r a i n s , th e day of r a i n would most l i k e l y be un detected.
Equations d e f in in g the r e l a t i o n s h i p between s o i l water con tent
in the top 21 cm o f th e s o i l p r o f i l e and L-band e m i s s i v i t y shown in
Fig. 34 (p. 63) are presented below.
The main p a r t of t h i s curve was
defined over a range o f water contents from n e a r - s a t u r a t i o n to a s o il
water con te nt of 4.0 cm. This p a r t of the curve is r ep r es en te d by a
o
l i n e a r equation (R = 0.9907):
Soil Water Content = -12.59223 eL + 15.11306
(III-l)
where Soil Water Content i s th e amount of water (in cm) in the top 21
cm o f th e s o i l p r o f i l e ,
i s th e L-band e m i s s i v i t y ( d i m e n s i o n l e s s ) .
This equat ion is v a l i d f o r values of
which t h e d i s c o n t i n u i t y o c c u r s ) .
<_0.88253 ( t h e p o in t a t
The mean d i f f e r e n c e between p r e d ic te d
values from t h i s equation and t h e p lo t te d point s was 1.9%.
However,
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84
t h i s does not inc lu de th e s c a t t e r e d poin ts near t h e d i s c o n t i n u i t y .
When
th ese were in c lu de d, the mean d i f f e r e n c e increased t o 3.6%.
A l e a s t sq uares r e g r e s s i o n through the p l o t t e d p o i n t s (Fig. 34,
p. 63) below a water c on t en t of 4.0 cm of water r e s u l t e d in a c o e f f i c i e n t
of det erm ina tio n equal t o zero.
However, i f one c a r e f u l l y examines
t h i s r e g i o n , a s l i g h t slope i s d e t e c t e d .
Therefore, two poin ts were
s e l e c t e d t o d e f i n e a l i n e a r f i t through t h i s i n s e n s i t i v e re g io n .
The
upper po in t was chosen as 4.0 cm of water and the corresponding
e m is s i v it y t h a t es ti m a t e s t h a t water cont ent (0.88253); t h e o th e r
s e l e c t e d p o i n t was t h e average e m i s s i v i t y a t 3.0 cm o f wate r.
The
equation defined by th e se two points i s :
Soil Water Content = -142.24490 eL + 129.53539
where the v a r i a b l e s ar e as p re v io u s ly defined.
(III-2)
Values o f L-band
e m is s i v it y must be g r e a t e r than 0.88253 but l e s s than or equal to 0.89
f o r t h i s equation t o be v a l i d .
The upper l i m i t f o r e m i s s i v i t y was s e t
a t 0.89 because t h e r a d i a t i v e t r a n s f e r model did n o t c a l c u l a t e
e m i s s i v i t i e s f o r L-band g r e a t e r than t h a t value.
A mean d i f f e r e n c e
o f 13.2% r e s u l t e d between p r ed ic te d values from t h i s eq uat ion and the
plotted points.
The r e l a t i o n s h i p t h a t was developed f o r the inverted s o i l p r o f i l e s
(Fig. 34, p. 63) i s r ep r es en te d by the following t h i r d o r d e r equation
(R2 = 0.9849):
Soil Water Content = 18691.29159 - 89552.441149 £|_ +
143072.04293 £|_2 - 76202.82082 0L3
(III-3)
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85
f o r the range of e m i s s i v i t i e s 0.59230 <_ e^ <_ 0.63.
defined e a r l i e r .
Variables a r e as
Pr edicted values from t h i s equation had a mean
d i f f e r e n c e o f 2.5%.
The bes t f i t equation r e p r e s e n t in g the one day change in
e m i s s i v i t i e s to es ti m a t e the amount o f water added to the lower portion
of t h e so il p r o f i l e (Fig. 46, p. 80) was a f i f t h or der polynomial
(R2 = 0.9807).
This equation i s :
Water Added = 991.67308 - 6121.45761
( A ex/ A
e^)
+
15109.28049 (Aex/Ae L) 2 - 18565.5536 (Aex/Ae l ) 3 +
11332.48706 (Aex/Ae l ) 4 - 2746.24344 (Aex/Ae l ) 5
(III-4)
where Water Added is the amount added (in cm) to the lower p a r t of the
s o i l p r o f i l e (21 to 150 cm d ep th );
Aex
is the change in X-band
e m i s s i v i t y f o r one day a f t e r th e r a i n (d im ensionless); Ae^ i s the change
in L-band e m i s s i v i t y f o r one day a f t e r the ra in (dimensionless).
The equation i s v a l i d over th e range 0.50 <_ ( aex/A e ^) £ 0.92.
For
a r a t i o of the change in e m i s s i v i t i e s l a r g e r than 0.92, one could use
l i n e a r e x t r a p o l a t i o n t o determine th e amount o f water added to
the lower
por ti on of th e s o i l p r o f i l e ; however, any amount of water l e s s than
0.5 cm added to th e lower s o i l p r o f i l e from i n f i l t r a t i o n i s i n s i g n i f i ­
ca nt .
The mean d i f f e r e n c e between t h e pr edi ct ed amount of added water
as c a l c u l a t e d by t h i s equat ion and t h e actual r e s u l t s was 1 0 . 2% f o r
amounts of added wate r g r e a t e r than 0. 5 cm.
When a l l p oin ts were
considered, the mean d i f f e r e n c e inc reased to 37.6 percent.
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86
To use th e s e equatio ns to estim a te s o il w ater c o n te n t in th e top
21 cm o f th e s o il p r o f i l e from L-band e m is s iv ity , th e follo w in g pro­
cedure would be used.
in Fig. 49.
A g e n e ra liz e d flow c h a r t of th e model is shown
E m issiv ity is t e s t e d each day to determine i f i t is le s s
than or g r e a t e r than the previous measurement.
band w ill be t e s t e d .
X-band as well as L-
Thus, a one-day h is to r y must be k ep t.
If
e m is s iv ity is le s s than th e previous d a y 's e m is s iv ity , a wet s o il
c o n d itio n is d e te c te d .
To determ ine whether or not th e s o i l m oisture
p r o f i l e i s in v e r t e d , th e change in L-band e m is s iv ity ( e m is s iv ity f o r the
day a f t e r r a in minus e m is s iv ity on the day o f r a in ) must be c a lc u la te d .
This cannot be done u n t i l th e e m is s iv ity is determined f o r th e following
day.
I f the change in L-band e m is s iv ity is g r e a t e r than 0.18 (th e
c r i t e r i a e s ta b l is h e d to c l a s s i f y an in v e rte d p r o f i l e ) , equation ( I I I - 3 )
i s used; o th e rw is e , equation ( I I I - l ) is used.
T h ere fo re , anytime a
wet s o i l c o n d itio n is d e t e c te d , th e re w ill be a one day d elay before
s o il w ater co n ten t in th e top 21 cm o f the s o i l p r o f i l e is p re d ic te d
f o r th e day on which r a in occurred.
I f e m is s iv ity is g r e a t e r than th e
previous d a y 's e m is s i v i t y , th e s o il is dry in g .
equation ( I I I - l ) is v a l i d ; however, i f
As long as eL <_0.88253,
> 0.88253, equation ( I I 1-2)
must be used to p r e d i c t th e w ater con tent in the 21 cm s o i l p r o f i l e .
E m issivity i s lim ite d to a maximum value o f 0.89.
With th e above pro­
cedure, a d ay-to-day account o f th e s o il m oisture s t a t u s in th e top 21
cm o f th e s o i l p r o f i l e is f e a s i b l e .
To e s tim a te th e amount of w ater added to th e s o il p r o f i l e below
21 cm, th e r a t i o o f th e change in X-band and L-band e m is s i v ity must be
c a l c u la te d .
Recall t h a t i t was necessary t o t e s t th e e m is s i v ity each
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87
START
~ T ~
I = 0
J = 0
PRINT
I = 1+1
i n
READ
DATA ( I)
CALCULATE
SOIL WATER
CONTENT 21cm
Eqn. ( I I I - 2 )
COMPUTE
ex ( I ) & e ,( I )
CALCULATE
SOIL WATER
CONTENT 21cm
Eqn. ( I I I - l )
IS
e (
I)>e(1-1
?
J = 0
CALCULATE
Aex ,
CALCULATE
SOIL WATER
CONTENT 21cm'
Eqn. ( I I I - l )
Ae
Aex / A e ,
CALCULATE
WATER ADDED
21 to 150 cm
Eqn. ( I I 1-4)
FIG. 49.
I = 1-1
/ i s \
------- K^Ae l >0 . 1
PRINT
tfwc21 ( I )
& WATERy
ADDED
CALCULATE
SOIL WATER
CONTENT 21cm
Eqn. ( I I 1-3)
G eneralized flow c h a r t of th e model.
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88
day to determ ine i f i t was le s s than th e previous measurement.
I f the
e m is s iv ity was l e s s than th e previous d a y 's e m is s i v ity , a wet s o il
c o n d itio n was d e te c te d .
At t h i s p o in t, X-band e m is s iv ity and L-band
e m is s iv ity f o r th e follow ing day must be determined b efo re any c a l c u l a ­
ti o n s a re performed.
A fter th e s e measurements a r e made, th e change in
X-band and L-band e m i s s i v i t i e s one day a f t e r th e r a i n a re c a l c u l a t e d ,
and th e r a t i o o f th e change in e m is s i v i t i e s is used in equ ation ( I I I - 4 )
to p r e d ic t th e amount o f water added to th e 21 to 150 cm la y e r o f the
s o il p r o f i l e .
Once th e amount o f w ater added to th e lower p o rtio n o f
th e s o il p r o f i l e i s e s tim a te d , i t is assumed t h a t t h i s q u a n t ity o f w ater
r e d i s t r i b u t e s i t s e l f throughout th e lower p r o f i l e .
Some o f i t may be
l o s t to deep p e r c o l a ti o n ; some o f i t may move to th e s o i l s u rf a c e by
c a p i l l a r y a c tio n and ev ap o ra te.
The remainder is s to re d in th e s o il
p r o f i l e f o r crop use.
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89
CHAPTER IV
EXPERIMENTAL STUDY
Soil w ater co n ten t from the n ear s u r fa c e la y e r down to a depth
o f 1.5 m i s re q u ire d to t e s t the model developed in Chapter I I I .
The
l i t e r a t u r e i s voluminous with s tu d ie s r e p o r ti n g measurements o f s o il
m oisture with depth r e s u l t i n g from varying amounts o f applied w ater.
However, n e a r - s u r f a c e s o il m oisture was always ignored.
I n v e s tig a to r s
who measured s o il m oisture in th e s u r fa c e la y e r s of a s o il did not
measure s o i l w ater content a t the deeper d e p th s.
Thus, a measurement
program was i n i t i a t e d to c o l l e c t s o i l m oisture content data in a 1.5 m
p r o f i l e du ring th e dry-down period fo llo w ing v ario u s amounts o f a p p lie d
w ater.
D escription o f Experimental S ite
The experim ental phase o f t h i s r e s e a rc h p r o j e c t was conducted in
f i e l d ly s im e te rs lo c a te d a t th e A g ric u ltu r a l Engineering Research
Laboratory a t College S ta t io n , Texas.
were given by H ile r (1969).
1.8 m in d e p th , were used.
D e ta ils o f t h i s i n s t a l l a t i o n
Twelve ly s i m e t e r s , 0.9 m in diam eter and
The experim ental la y o u t o f th e t e s t area
c o n s is te d o f fo u r rows o f ly sim ete rs with t h r e e ly sim ete rs per row.
These ly s im e te rs were pro tec ted from r a i n f a l l by a movable s h e l t e r
which a u to m a tic a lly covered the ly s im e te rs when r a in began and moved
o f f when r a i n f a l l ceased.
The o r i g i n a l s o i l contained in t h e s e ly s im e te rs was an u ndisturbed
core o f a la y e re d s o i l . Due to e x te n siv e sampling o f th e s o il p r o f i l e
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90
in th e se ly s im e te rs through th e y e a r s , i t was decided t h a t t h i s s o il
should be re p la c e d .
Since th e two-probe d e n s ity gauge was to be used
to measure s o i l w ater c o n te n t, p a r a l l e l access tubes were fix e d in to
place in each ly s im e te r p r i o r to f i l l i n g them with s o i l .
s e le c te d f o r t h i s study was a sandy loam.
The s o il
This s o i l was mixed and
c a r e f u l l y tamped in to the ly s im e te rs to make each p r o f i l e as uniform
and as n e a rly a l i k e as p o s s ib le .
e t e r s in i t s a i r - d r y s t a t e .
The s o il was packed in to th e lysim ­
A fte r tamping the s o il in to th e ly s im e te r s ,
th e s o il p r o f i l e was s a tu r a te d by adding w ater through th e porous
ceramic f i l t e r system in the bottom o f each ly s im e te r.
There was very
l i t t l e o r no s e t t l i n g of th e s o il p r o f i l e the second time i t was
s a tu r a te d and dewatered.
Methods
Data were c o lle c te d during each o f th e four seasons which began
during th e s p rin g o f 1978 and ended du ring th e w in te r o f 1979.
The s o il
in and around th e ly sim ete rs remained bare through the course o f t h i s
study.
Two major v a r ia b le s measured a t th e experimental s i t e p e r ti n e n t
to t h i s study were s o il m oisture c o n te n t and s o il tem p eratu re. Soil mois­
t u r e c o n te n t was measured with a tw o-probe d e n s ity gauge (Model 2376,
T ro x ler E le c tr o n ic L ab orato ries) a t depths o f one to f i f t e e n cm in one cm
increm ents, f i f t e e n to tw en ty -fiv e cm in two cm increm ents, tw e n ty -fiv e
to f i f t y cm in f iv e cm increm ents, and f i f t y to one hundred f o r t y cm in
te n cm increm ents.
Copper-constantan thermocouples were used to measure
s o il tem perature j u s t under the smooth s o il su rface (approxim ately 0.2
cm), a t depths o f one to f i f t e e n cm in two cm increm ents, a t 18 cm, and
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91
a t 22 cm.
Soil tem perature was measured in only two ly sim ete rs and was
recorded hou rly.
Water was a p p lied to th e s o il in th e ly s im e te rs with a g r ic u ltu r a l
spray no zzles.
One wide ang le, f u l l cone, low p re s s u re nozzle was mount­
ed over th e c e n t e r o f each ly s im e te r a t a h e ig h t o f 0 .4 m to insu re
complete coverage o f th e e n t i r e s o il s u r f a c e .
r a t e o f 1.8 x 10
-5
Water was applied a t a
3
m / s e c (approxim ately 4 i n / h r ) and a t a gauge pressu re
of 55.16 KPa (8 p s i ) .
The nozzles were c a l i b r a t e d each time w ater was
ap p lied .
Two-Probe Density Gauge C a lib ra tio n
Gamma-ray a t t e n u a t io n was o r i g i n a l l y used in s o i l physics f o r
measuring bulk d e n s i t y .
Since th e measurement i s b a s i c a l l y one of wet
d e n s i t y , i t can a l s o be used f o r measuring s o i l w a te r c o n te n t (Reginato
and Van B avel, 1964).
Gurr (1962) pointed out t h a t s o il dry d e n s ity must
be known and remain unchanged a t each measurement lo c a tio n in order to
use gamma-ray a t t e n u a t i o n to ob tain s o il m o istu re d a t a .
The p rin c ip a l
j u s t i f i c a t i o n f o r using gamma a tte n u a tio n to measure s o i l water con tent
in s i t u r e s id e s in th e reso lv in g power o f th e method, in o th e r words, the
volume o f s o i l seen by th e d e t e c t o r (Reginato and Van Bavel, 1964).
Van
Bavel (1959) has shown t h a t th e r e s o lu tio n o f th e method is on th e o rd er
o f one cm which means t h a t th e s o il p r o f i l e can be scanned in one cm
th i c k l a y e r s .
Monoenergetic gamma rays passing through a s o i l - w a t e r system are
a tte n u a te d according to th e expression (Reginato and Jackson, 1971):
lnl = l n l 0 - xV s - xV w ev
(IV-1)
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92
where I is th e count r a t e through th e ab so rb er, I
is the count r a t e
with no absorb er (zero d e n s i t y ) , x i s th e absorber th ic k n e s s (cm), us
is th e mass a t t e n u a t io n c o e f f i c i e n t f o r dry s o i l (cm / g ) , uw is the mass
o
a tte n u a t io n c o e f f i c i e n t f o r w ater (cm / g ) , pg i s th e s o i l bulk d e n s ity
a t each measurement p o in t ( g / c m ) , pw is th e d e n s ity of w ater (taken as
3
3
3
1.00 g/cm ) , and 9y is th e v olu m etric w ater c o n ten t (cm /cm ).
to use th e above e q u a tio n , values f o r IQ,
In o rd er
and uw must be determ ined.
Procedures to c a l i b r a t e a two-probe d e n s ity gauge have been d ev el­
oped by Reginato and Van Bavel (1964).
through a s e r i e s o f g l a s s p l a t e s .
I
is determined by ta k in g counts
A varying d e n s ity e f f e c t i s c re a te d by
in c re a sin g th e number o f g la s s p l a t e s between th e p a r a l l e l access tu b e s.
P lo ttin g th e log o f th e count r a te versus d e n s ity produces an in v e rse
lin e a r re la tio n sh ip .
The value f o r I
is estim ated by e x t r a p o la t in g
th e b e s t f i t l i n e through th e d a ta poin ts to zero d e n s it y .
A f te r d e t e r ­
mining I 0 , us is c a l c u l a t e d by measuring th e count r a t e through a column
of oven-dry s o il i n s e r t e d end t o end between p a r a l l e l access tu b e s.
Since th e s o i l is oven d r y , th e term co n tain in g m o istu re c o n te n t in
equation (IV-1) drops o u t, and th e eq uation is d i r e c t l y solved f o r y .
Bulk d e n s ity of th e s o i l contained in the column is determ ined by weigh­
ing a l l th e s o il and d iv id in g by th e volume o f th e c o n t a in e r .
The value
f o r yw is e a s i l y determ ined by p la c in g p a r a l l e l access tubes in a con­
t a i n e r o f w ater and o b ta in in g th e count r a t e (Reginato and Jackson,
1971).
Here, a g a in , e q u atio n (IV-1) i s s im p lif ie d by d e l e t i n g th e term
containing s o il e f f e c t s ; th u s , yw is r e a d i ly c a l c u la te d .
S a ti s f a c t o r y r e s u l t s were not obtained when c a lc u la te d m oistu re
co n ten ts from eq u atio n (IV-1) using values o f I , us » and uw obtained
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93
from the above procedures were compared to measured m o istu re c o n te n ts .
D ifferen ces between c a lc u la te d and measured m o istu re c o n te n ts were
g r e a t e r than 10 p e rc e n t f o r some samples.
The probable cause of th e s e
e r r o r s was due to th e small diam eter (7 cm) o f th e tub e used to contain
th e s o il column.
Thus, an a l t e r n a t e procedure was developed to d e t e r ­
mine th e c a l i b r a t i o n c o n s ta n ts .
For t h i s a l t e r n a t e procedure, I
was again determined f i r s t .
This
value was determined by taking a s e r i e s o f counts through 8 .9 cm
diam eter aluminum bars o f various le n g th s placed between two p a r a l l e l
access tubes a known d is ta n c e a p a r t which in essence c re a te d a varying
d e n s it y e f f e c t .
The d ata were p lo tte d as shown in F ig . 50 and e x t r a ­
p o la te d to zero d e n s it y .
The y - a x is i n t e r c e p t (z e ro d e n s ity ) f o r the
b e s t f i t equ atio n through th e s e data (R^ = 0.9998) was 272442 counts
p er minute.
Soil a t v ario u s m oisture co n ten ts ranging from oven dry
to f i e l d c a p a c ity was packed in to a p le x ig la s s box 15 cm wide, 45 cm
long, and 15 cm deep co n tain in g permanently i n s t a l l e d access tu b e s .
The
count r a t e ( I ) through th e s o i l medium was determined a t s e v e ra l d e p th s.
Upon completion o f th e gamma measurements, th e e n t i r e s o i l mass was
weighed and d rie d to determ ine th e g ra v im e tric m o istu re c o n te n t and dry
d e n s ity (pg ) from which th e volum etric m oisture c o n te n t (ev ) was
c alcu la ted .
The mean count r a t e , dry d e n s it y , and volum etric m oisture
c o n te n t from a l l th e samples were used in a m u l tip l e l i n e a r re g r e s s io n
a n a l y s i s to determ ine th e c o e f f i c i e n t s r e p r e s e n tin g IQ, ps , and vw»
IQ
determined by t h i s procedure was reasonably c lo s e to t h a t o b ta in ed by
th e o th e r method (269077 cpm as opposed to 272442 cpm).
o f d eterm in a tio n was 0.9996.
The c o e f f i c i e n t
C a lib r a tio n c o n s ta n ts determined by t h i s
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94
IQ6 r
s
\
s
N
10s
\
\
UJ
I—
ID
R = 0.9996
2
H—I
2
\
cn
3
O
u
1 QU
103
0. 0
0.5
1.0
1.5
DENSITY
2.0
IG/CC)
2.5
3.0
FIG. 50. R e la tio n sh ip between count r a t e and bulk d e n s ity f o r the
two-probe d e n s it y gauge determined from v a rio u s le n g th aluminum b ars.
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95
2
second procedure f o r I Q, us » and uw were 269077 cpm, 0.061313 c m / g ,
2
and 0.060329 cm / g , r e s p e c t iv e l y .
M oisture conten t c a lc u la te d by
equation (IV-1) using th e above c a l i b r a t i o n c o n stan ts d i f f e r e d from
measured m o istu re conten t by l e s s than one percent by volume ( le s s
than f o u r p e r c e n t d if f e r e n c e ) over a lim ite d s o il m o istu re range (16
to 29 p e r c e n t by volume).
Due t o th e la rg e number of s o il m oisture measurements to be made
on any given day, i t was o f i n t e r e s t to determine whether or not a
s i g n i f i c a n t d if f e r e n c e e x is te d in r e s u l t s obtained from a 15 second
counting period as opposed t o a one minute counting p e rio d .
To do t h i s ,
a s e r i e s o f count r a te s through vario us length s o f aluminum bars which
re p re se n te d 14 d i f f e r e n t d e n s i t i e s ranging from 0.98 g/cm
were ob tain ed f o r th e two counting p e rio d s .
3
t o 2.80 g/cm
3
The null hyp o th e sis of
equal means was te s te d by m u ltip ly in g the 15 second count r a t e by four
to make i t e q u iv a le n t to a one minute count r a t e .
R esu lts from the
t - t e s t s in d ic a te d t h a t th e re was n ot a s i g n i f i c a n t d i f f e r e n c e between
15 second cou nt r a t e s and one minute count r a te s a t th e 0.01 le v e l of
s ig n if i c a n c e f o r th e 14 d i f f e r e n t d e n s i t i e s .
Measurement Procedures
Soil m o istu re measurements made in th e ly s im e te rs were taken with
a 15 second counting period.
Depths of measurement ranged from one cm
to 140 cm below th e s o il s u r f a c e .
Even w ith t h i s s h o r t counting tim e,
approxim ately f o u r hours were re q u ir e d to make a ll measurements per day.
Soil m o istu re was measured p r i o r t o th e i n i t i a t i o n of each seasonal
experiment.
A f te r th e se measurements, w ater was ap p lied in amounts of
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96
1.27 cm (0 .5 i n ) , 2.54 cm (1.0 i n ) , 3.81 cm (1 .5 i n ) , and 5.08 cm (2 .0
in) with each amount repeated th r e e tim es.
As soon as the w ater
i n f i l t r a t e d , s o i l m oistu re measurements were taken.
Following th e post
i n f i l t r a t i o n measurements, s o il m o istu re was measured around midday on
a d a ily b a s is f o r f i v e days to o b ta in th e maximum d a i ly change.
Soil
m oisture measurements were then made th r e e times a week f o r approxim ately
two weeks.
At th e end o f t h i s p e r io d , w ater was again applied to the
ly sim e te rs in amounts of 1.27 cm, 2.54 cm, and 3.81 cm in a fash io n such
t h a t th e second a p p lic a tio n was l a r g e r than th e f i r s t a p p l ic a t io n , the
same as th e f i r s t a p p l ic a t io n , o r l e s s than th e f i r s t a p p lic a tio n (Table
4 ).
Each amount was repeated fo u r tim e s .
followed th e schedule previously o u tl in e d .
Soil m oisture measurements
A fte r the th i r d week, s o i l
m oisture was measured on a weekly b a s is u n ti l th e next seasonal e x p e r i­
ment began.
TABLE 4.
Lysimeter
Row
AMOUNT OF WATER (cm) APPLIED TO THE LYSIMETERS
DURING EACH SEASONAL EXPERIMENT
Water
A pplication
Amount of Water Applied
to Lysimeter
L
C
R
1
F irst
Second
1.27
1.27
1.27
2.54
1.27
3.81
0c.
F irst
Second
2.54
1.27
2.54
2.54
2.54
3.81
00
F irst
Second
3.81
1.27
3.81
2.54
3.81
3.81
A
F irst
Second
5.08
1.27
5.08
2.54
5.08
3.81
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97
The experim ent re p r e s e n tin g th e sp rin g season was i n i t i a t e d on
May 1, 1978, followed by a r e a p p l ic a t io n o f w ater on May 23.
The summer
experiment began on Ju ly 24, 1978, w ith w ater ap p lied again on
August 16.
October 28, 1978, was the beginning d a te f o r th e f a l l
experiment followed by th e second a p p lic a tio n o f w ater on November 16.
Since th e ly s im e te r i n s t a l l a t i o n was in a d esign ated c o n s tr u c tio n
area f o r a new b u il d in g , the time period a s s o c ia te d with th e w inter
experiment was reduced in r e l a t i o n to th e o th e r seasonal experim ents.
The experiment was i n i t i a t e d on January 9, 1979; w ater was ap p lied
again on January 24.
In o rd e r to not d i s t u r b th e s o il p r o f i l e during the course o f the
stu d y , bulk d e n s it y was determined a t each measurement depth in each
ly s im e te r a t th e end o f th e w in te r experiment.
To determ ine bulk
d e n s it y , measurements were made with the two-probe d e n s ity gauge as
usual with th e excep tio n o f u sing a longer counting time (one m in ute).
S h o rtly a f t e r ta k in g th e instrum en t measurement, s o i l samples were
c o lle c te d between th e access tubes a t the d e s ire d depth to determine
the m oisture c o n te n t on a dry weight b a s is .
Knowing the g ra v im e tric
s o il m oisture c o n te n t and the gamma a tte n u a te d count r a te ,- bulk d e n s ity
was determined from th e derived r e l a t i o n s h i p between count r a t e and
d e n s ity shown in Fig. 50 (p. 94).
The c a lc u la te d bulk d e n s i t i e s were
assumed to have remained c o n s ta n t throughout the d u ra tio n o f the study.
At t h i s p o i n t , th e bulk d e n s ity v alues and p revious measurements o f
t o t a l d e n s it y were used to c a l c u l a t e s o il m oisture co n ten ts f o r the
c o lle c te d d a t a .
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98
Day to day v a r ia tio n s in th e gamma probe were c o rre c te d by r e l a t i n g
a d a i l y standard count to th e long -tim e average standard count obtained
during the study as suggested by Gurr (1962).
The 15 second c o rre c te d
count was m u ltip lie d by fo u r to make i t e q u iv a le n t to a one minute
count.
Soil m oisture co n ten t was then c a l c u l a t e d by equation (IV -1).
Soil m oisture d ata and s o il tem perature d a ta were in p u t in to the
r a d i a t i v e t r a n s f e r model describ e d e a r l i e r in t h i s paper.
This model
c a l c u la te d the thermal microwave em ission t h a t would be expected to be
measured by p a s s iv e microwave rad io m ete rs lo oking d i r e c t l y a t the s o il
s u rfa c e in each ly s im e te r a t a zero angle o f in c id en ce .
As p rev io u sly
s t a t e d , s o il tem perature was measured in only two ly s im e te rs in which
very l i t t l e v a r i a t i o n e x i s t e d .
Thus, t h e s o i l tem perature p r o f i l e
assumed f o r th e o th e r ly s im e te rs was an average tem perature c a lc u la te d
from the two measured p r o f i l e s a t the time s o i l m o isture data were
c o l l e c t e d in a given ly s im e te r.
Soil te m p eratu re below 22 cm was s e t
equal to the s o i l tem perature recorded a t 22 cm.
Observations from Measured Data
R esu lts from some o f the c o l le c t e d d a ta a re p resented below.
Soil
m o isture measurements were made in a bare sandy loam s o il contained in
ly s im e te rs with a two-probe d e n s ity gauge a t depths o f one cm to 140 cm
below th e smooth s u rfa c e .
V ariab le amounts o f w ater were applied to
th e s o il in th e s e ly s im e te rs tw ice d urin g each seasonal experiment as
o u tlin e d in the previous s e c ti o n .
Soil w ater c o n te n t was c a lc u la te d by
equ atio n (IV-1) a t each measurement dep th .
C alcu lated m oisture co n ten ts
a t depths o f one, two, and th r e e cm were very s u s p i c io u s , e s p e c ia lly
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout perm ission.
99
a f t e r th e s o i l s t a r t e d d ry in g .
As long as the s o il was w et, c a lc u la te d
s o il m oisture c o n te n ts appeared reaso n ab le in the n e a r -s u r fa c e depths.
DeVries (1969) has s ta t e d t h a t the three-dim ensional geometric
shape o f the gamma beam i s not a pyramid with a base 3.81 cm (diam eter
of the d e t e c to r ) by 1.25 cm (th ic k n e s s o f the Nal c r y s t a l ) and a h eig h t
equal to the a t t e n u a t i o n path le n g th .
He suggested, in s te a d , t h a t th e
gamma photon beam has a volume o f in flu e n c e s im ila r in shape to t h a t
in d ic a te d in Fig. 51.
by the
137
A p ro p o rtio n o f th e 0.662-Mev photons em itted
Cs source i s s u b je c t to low angle s c a t t e r i n g which causes a
reduction in energy o f th e s e s c a tt e r e d photons.
When a count i s taken
in a s o il- w a t e r system, th e se s c a tt e r e d photons c o n trib u te to the
count because t h e i r energy s t i l l f a l l s w ithin the range o f th e window
se ttin g .
However, when a count i s taken near a s o i l - a i r i n t e r f a c e ,
p a r t o f th e photons s u b je c t to low angle s c a tt e r i n g escape in to the
a i r r e s u l t i n g in a reduced count r a t e .
APPROXIMATE VOLUME OF
INFLUENCE IN WATER
rf ■*',i
DETECTOR
SOURCE
„
Jal
CRYSTAL
GAMMA-BEAM
FIG. 51. Approximate p la n a r geom etric shape o f gamma-beam, a f t e r
DeVries (1969).
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
100
When s o il m oisture co n te n t in th e s u rfa c e la y e r s were considered
su sp e ct on any given day, they were d e le te d from th e d a ta .
The r e s t of
the d a ta were then smoothed t o e lim in a te e r r a t i c changes in water con­
t e n t through th e s o il p r o f i l e .
This was accomplished by simply adding
th e s o il m oisture c o n te n t a t a p a r t i c u l a r depth to th e s o il m oisture
co ntent one la y e r d i r e c t l y above and below t h a t d ep th , c a l c u la tin g the
average, and a s s ig n in g t h i s average to the depth in q u e s tio n .
Of
co u rse , th e f i r s t and l a s t la y e rs were t r e a te d d i f f e r e n t l y due to non­
e x i s t e n t s o il m oisture data above the f i r s t la y e r o r below the l a s t
layer.
For tho se days t h a t had the n e a r- s u rf a c e dep th s o f s o il water
c o n te n t d e l e t e d , th e smoothed s o il m oisture p r o f i l e was p lo tte d and
th e curve e x tra p o la te d to th e s o il s u rfa c e to e s tim a te the s o il water
co n ten t in th e s u rf a c e la y e r .
Soil m oisture d a ta re p re s e n tin g the f i r s t w ater a p p lic a tio n during
the sp rin g experiment was d e le te d .
The r a in o u t s h e l t e r malfunctioned
during a r a in storm which occurred two days a f t e r w ater was app lied to
th e ly s im e te r s .
As a r e s u l t , th e s o il in some o f th e ly s im e te rs
received unknown q u a n t i t i e s o f p r e c i p i t a t i o n .
Another r a in o u t s h e l t e r
m alfunction occurred during th e f i r s t f a l l experim ent.
Since the
experiment was f a r enough in to the drying c y c le , i t d id not s u f f e r any
consequences from th e added w ater.
However, a l l s o i l m oisture data
c o lle c te d a f t e r the r a in were d eleted from th e d a ta s e t .
Soil m o istu re p r o f i l e s were p lo tte d as a time s e r i e s f o r the
remaining d a ta to show w e ttin g and drying o f th e s o i l p r o f i l e from
ap plied w ater.
and 55.
Some o f these p r o f i l e s a r e shown in F igs. 52, 53, 54,
These f ig u r e s r e p r e s e n t the s o il m oisture s t a t u s f o r the
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
101
o
0
MOrSTURE
5
10
CONTENT
15
20
(% BY
25
VOLUME)
30
35
o
ro
o
U)
o
COin
Q °
SPRING
o
O
m
3
x
* 142
o 143
x
°
00
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156
170
n
w o
o
o
o
10
o
FIG. 52. Soil m o istu re p r o f i l e s measured in ly s im e te r 3R during the
spring f o r the days shown. J u lia n day 142 r e p r e s e n ts the s o il
m oisture s t a t u s p r i o r t o th e 4.8 cm i r r i g a t i o n .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
102
0
MOISTURE
5
10
CONTENT
15
20
(X
25
BY
VOLUME)
30
35
40
SUMMER
*
o
x
+
o
*
226
228
229
230
233
240
FIG. 53. Soil m o istu re p r o f i l e s measured in ly s im e te r 3R during the
surrener f o r th e days shown. J u lia n day 226 r e p r e s e n ts the s o il
m oisture s t a t u s p r i o r to the 3.8 cm i r r i g a t i o n .
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103
MOISTURE
5
10
CONTENT
15
20
(X
25
BY
VOLUME)
30
35
* 319
o 320
321
322
o 324
326
* 331
338
345
FIG. 54. Soil m o isture p r o f i l e s measured in ly s im e te r 3R during the
f a l l f o r th e days shown. J u lia n day 319 r e p r e s e n t s th e s o il
m oisture s t a t u s p r i o r to th e 5 .4 cm i r r i g a t i o n .
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
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105
second w ater a p p l ic a t io n in ly s im e te r 3R during the s p r in g , summer,
f a l l , and w in te r ex perim ents, r e s p e c t iv e l y .
The p lo t te d data p o in ts
a r e somewhat m isleading s in c e they r e p r e s e n t an average m oistu re co n ten t
from th e smoothing technique r a t h e r than th e actu a l measured data a t
each depth.
The data f o r d i f f e r e n t days were la b e le d by use of
d i f f e r e n t symbols f o r each day t h a t p r o f i l e s a re shown.
The amount
of w ater a p p lie d t o t h e s o i l in t h i s ly s im e te r f o r th e second w ater
a p p l ic a t io n during each seasonal experiment was 3.81 cm.
However,
a f t e r pla n im eterin g th e area between th e i n i t i a l s o i l m oistu re p r o f i l e
(design ated by a s t e r i s k s ) and th e s o il m o isture p r o f i l e measured as soon
as p o s s ib le a f t e r w ater i n f i l t r a t i o n (re p re s e n te d by o c ta g o n s), th e
planim etered e q u iv a le n t amount of w ater was found t o be d i f f e r e n t from
t h a t supposedly a p p lie d .
This was probably due to p re s s u re changes
w ithin th e i r r i g a t i o n system w hile applying w ater.
Since th e o p eratin g
p ressu re used to apply the w ater was f a i r l y low (55.16 KPa), m a in taining
a c o n s ta n t p re s s u re a t each nozzle was v i r t u a l l y im possible with the
system used.
The amount o f w ater a c t u a l l y ap p lied t o th e s o i l on the
second a p p l ic a t io n in ly s im e te r 3R f o r th e s p r in g , summer, f a l l , and
w inter experiments was approxim ately 4.8 cm, 3.8 cm, 5.4 cm, and 3.0
cm, r e s p e c t iv e l y .
Consequently, each time s e r i e s p l o t o f the s o il
m oisture p r o f i l e s was planim etered to determine th e actu a l amount of
water ap p lied to th e s o i l (Table 5 ).
Very r a r e l y did th e amount of
applied w ater as measured with th e planim eter agree w ith th e a lle g e d
applied q u a n tity shown in Table 4 (p. 96).
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
Reproduced with permission
TABLE 5.
ACTUAL AMOUNT OF WATER APPLIED TO THE SOIL IN EACH LYSIMETER DURING
THE SEASONAL EXPERIMENTS
of the copyright owner. Further reproduction
Season
F a ll
Summer
S pring
W inter
prohibited without p erm ission
Lysim­
e te r
Second
A p p lic a tio n
F irst
A p p lic a tio n
Second
A p p lic a tio n
F irst
A p p lic a tio n
Second
A p p lic a tio n
F irst
A p p lic a tio n
Second
A p p lic a tio n
1L
2.07
1.71
1.44
2 .06
1 .6 8
1 .6 6
2 .2 2
1C
2.21
2 .0 0
2.48
2.47
3 .9 9
1 .8 8
3.52
1R
4.5 6
2.21
4.8 0
1.63
6.41
1.58
3.09
2L
1.69
2 .95
1.81
3.33
1.73
3.24
1.46
2C
2.31
2.62
2.39
2.54
2 .4 9
2 .3 4
2.24
2R
3.36
2 .94
4.12
3.23
4 .8 3
3.03
3.28
3L
1 .6 8
4.31
1.71
6.97
1.85
5.32
1.87
3C
3.45
6 .1 2
3.05
4.6 8
4 .0 0
5.17
3.66
3R
4 .82
3.97
3.85
5.63
5.44
4 .2 4
2 .99
4L
1 .2 2
4.71
1.81
9.52
1.77
5.22
1.29
4C
2 .99
4 .72
1.58
3 .93
2.61
5.09
2.65
4R
3.88
7.91
3.38
6 .37
3 .93
7.05
3.22
o
O')
107
Even though equal amounts o f water were not a p p lied to the s o il in
ly s im e te r 3R f o r th e second a p p l ic a t io n during th e four se a s o n s ,
d i f f e r e n c e s in dry in g r a t e o f th e s o il are very obvious as in d ic a te d in
F igs. 52 through 55 (pp. 101 through 104). These d if f e r e n c e s a re due,
f o r the most p a r t , to d i f f e r e n t seasonal c lim a tic c o n d itio n s .
E m is s iv itie s c a l c u la te d by th e r a d i a t i v e t r a n s f e r model from s o il
m oisture measured in ly s im e te r 3R and s o il tem perature d a ta a l s o show
th e d if f e r e n c e s in drying r a t e o f the s o il during th e fo u r seasons
(F ig. 56).
The change in e m is s iv ity the f i r s t day a f t e r w ater a p p l ic a ­
ti o n is w itho ut doubt g r e a t e s t during the summer and l e a s t during the
w in te r.
This is as expected s in c e th e p o te n tia l f o r e v a p o ra tio n is
la rg e during th e summer and small during the w in te r.
Changes in
e m is s iv ity from day to day a re d e f i n i t e l y a good i n d i c a t o r o f the
drying r a t e o f a s o i l as hypothesized by Blanchard (1979) and Blanchard
and Bausch (1979).
Measured s o il w ater c o n te n t in the top 21 cm o f the s o i l p r o f i l e
and L-band EQSM c a l c u la te d by th e r a d i a t i v e t r a n s f e r model were
p lo t te d f o r th e f o u r seasonal w ater a p p lic a tio n s in ly s im e te r 3R.
These
data a re presented in Fig. 57 f o r th e s p rin g , summer, f a l l , and w in te r
experim ents.
The same general tren d e x i s t s between L-band EQSM and
measured s o il w ater c o n te n t in th e top 21 cm as was shown f o r th e
sim ulated r e s u l t s .
L-band EQSM underestim ated the s o i l w ater c o n te n t
most the f i r s t day a f t e r w ater was a p p lie d .
approxim ately 0.3 cm o f w ater.
This d i f f e r e n c e was
D ifferen ce s between L-band EQSM and
measured s o i l w ater c o n te n t du rin g th e s p rin g , f a l l , and w in t e r ,
e s p e c i a l l y , e x is te d f o r lo ng er p eriods o f time than during th e summer.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
Reproduced
with permission
o>ft
o
of the copyright owner. Further reproduction
a>%
a
SPRING
t IRRIGATION
SUMMER
f IRRIGATION
P
CD
175
O
180 '"220
225
230
235
240
245
25 0
255
260
x X-Bfl^D EMIS
o L-BflND EMIS
a>
o
CD
prohibited without p erm ission .
o
ra
FALL
t IRRIGATION
J----------- 1 _
315
320
325
330
335
340
345
WINTER
t IRRIGATION
_i
-jLi_
350
3 55 ° 2 0
TIME
( DAYS)
25
30
35
40
45
50
55
FIG. 56. Bnissivities calculated by the radiative transfer model from measured soil water content in
lysimeter 3R and soil temperature for the spring, summer, fall, and winter experiments.
60
O
00
Reproduced
with permission
00
o
>
1
?40
I_______ L
»1*5
150
|5 5
160
165
170
CO
|8 ?
o
220
22 5
J L
23 0
4------------ 1________ U
235
210
21 5
25Q
255
26?
x SOIL WATER CONTENT
o L-BANO EQSM
O
SI*
Q
cn
C3
Ul
|7 5
SUMMER
f IRRIGATION
o
(D
o
CO
prohibited without p erm ission
o
o
o
Al
o
FALL
f IRRIGATION
o
20
HINTER
t IRRIGATION
25
30
35
40
50
55
TIM
E (DATS)
FIG. 57. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e in
l y s im e te r 3R and L-band EQSM as c a l c u l a t e d by t h e r a d i a t i v e t r a n s f e r model from measured s o i l w a te r
c o n t e n t and s o i l te m p e r a tu r e f o r th e s p r i n g , summer, f a l l , and w i n t e r e x p e rim e n ts .
SOIL WRTEfi CONTENT
of the copyright owner. Further reproduction
AJ
SPRING
t IRRIGATION
(CM)
iO
no
T herefo re, L-band EQSM would probably be b e t t e r r e l a t e d to the s o il
w ater co n te n t in a th in n e r la y e r o f s o i l .
The maximum d iff e r e n c e
between L-band EQSM and s o il w ater co n te n t in th e top 21 cm of the s o il
p r o f i l e from a l l th e p lo tte d d a ta was approxim ately one cm of water
which occurred on th e day w ater was a p p lie d .
This was th e r e s u l t of
a 1.6 cm a p p lic a tio n o f water on a very dry s o i l p r o f i l e .
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m
CHAPTER V
DISCUSSION OF RESULTS
Algorithms developed from th e simulated r e s u l t s f o r a homogeneous
loam -like s o i l , eq u atio n s ( I I I - l ) to ( I I I - 4 ) , were used to p r e d ic t s o il
water content from d a ta measured in ly s im e te rs .
E m is s iv itie s req u ire d
in th e p r e d i c t o r eq uatio ns were c a lc u la te d by a r a d i a t i v e t r a n s f e r
model (Newton, 1977) from measured s o il w ater co n ten t and s o il tempera­
tu re.
P redicted s o il w ater c o n te n t was compared to measured s o il
m oisture d a ta .
V e r i f i c a t i o n o f the Model
F i r s t Layer Algorithm
Since L-band EQSM and measured s o il w ater co n ten t (F ig . 57, p. 109)
showed the same general tr e n d f o r each of th e fo u r s e a s o n s , c a l c u la te d
L-band e m i s s i v i t i e s and measured s o il w ater content in th e top 21 cm
of the s o il p r o f i l e were p l o t te d w ith a l l fo u r seasons combined
(Fig. 58).
Data p o in ts r e p r e s e n tin g in v e rted p r o f i l e s were d e le te d .
Soil m oisture p r o f i l e s were c l a s s i f i e d as being in v e rte d i f X-band
EQSM was la r g e r than L-band EQSM, both of which were c a l c u la te d by the
r a d i a t i v e t r a n s f e r model.
The a lg o rith m developed from th e sim ulated
r e s u l t s to e s tim a te s o i l w ater c o n te n t in th e top 21 cm o f th e s o il
p r o f i l e from L-band e m is s i v ity (F ig. 34, p. 63) was a d ju s te d to th e
measured d a ta .
For th e sim ulated r e s u l t s , th e d i s c o n t i n u i t y occurred
a t a s o il w ater co n ten t o f 4 .0 cm; whereas, f o r the measured d a t a , t h i s
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112
LU
f-
oo
CO
0 .3
0 .5
0 .6
0 .7
0 .8
L-BfiND E M I S S I V I T Y
0 .9
1.0
FIG. 58. R e la tio n sh ip between measured s o il w ater c o n ten t in th e top
21 cm o f th e s o i l p r o f i l e and L-band e m i s s i v ity as c a lc u la te d by the
r a d i a t i v e t r a n s f e r model f o r s p r in g , summer, f a l l , and w in ter d a ta .
Inverted s o i l m oisture p r o f i l e s were d e l e te d .
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113
d i s c o n t i n u i t y occurs a t approxim ately 3 cm o f water.
The model was
developed f o r a h y poth etical lo a m -lik e s o i l ; s o il w ater c o n te n t and
s o i l te m perature were measured in a sandy loam s o i l .
Since a sandy
loam s o il holds le s s water than a loam s o i l , the d i s c o n t in u it y would
obviously occur a t a lower water c o n te n t.
This d is c o n t in u it y or
t r a n s i t i o n m o istu re c o n te n t in c r e a s e s w ith in c re ased c la y c o n te n t in
th e s o il as measured by Newton (1977).
Also, since th e w ater and heat
balance model used to sim ulate s o i l w ater co n ten t has not been v e r i f i e d ,
f in e tuning t h i s model to f i t measured d a ta should be a c c e p ta b le .
The alg o rith m to p r e d ic t s o il w ater c o n te n t in th e uppermost 21 cm
o f th e s o il p r o f i l e was superimposed on th e s p rin g , summer, f a l l , and
w in te r d a ta as shown in Figs. 59, 60, 61, and 62, r e s p e c t i v e l y , w ith the
i n f l e c t i o n p o in t s e t a t a s o il w ater c o n te n t o f 3.0 cm.
These d ata
r e p r e s e n t a l l measurements taken in th e tw elve ly s im e te rs during each
seasonal experim ent.
measurement e r r o r .
S c a tte r in g o f th e d a ta i s most l i k e l y due to
I r r e s p e c ti v e o f th e s c a t t e r , the algo rith m appears
to f i t the measured data f a i r l y w e ll.
d e le te d in th e s e f i g u r e s .
In v erte d p r o f i l e data were again
T h e re fo re , th e m a jo rity o f th e p lo t te d data
p o in ts r e p r e s e n t th e s o il m oisture s t a t u s on th e day a f t e r i r r i g a t i o n
and throug ho ut th e remainder o f th e d ry in g p e rio d .
However, t h e r e are
a number o f d a ta p o in ts p l o t te d in F ig s . 59 through 62 t h a t r e p r e s e n t
the s o i l w ater c o n te n t on the day o f i r r i g a t i o n ; th e se p o in ts r e p r e s e n t
a very wet p r o f i l e .
Most of th e se p a r t i c u l a r p o in ts occurred during
the f a l l and w in te r experiments.
Data p re s e n te d in F igs. 59 and 60
f o r th e s p rin g and summer experiments a r e somewhat m isleading s in c e
most o f th e p l o t t e d p o in ts r e p r e s e n t a dry s o i l .
This is due to the
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
114
CO
co
s
u
1“ U>
2
LU
h2
CO
,G 0
L
U
_l
O
cn
SPRING
o *—
0 .3
0.5
0.6
0 .7
0.8
L-BRND EMI S S I V I T Y
0.9
1.0
FIG. 59. R e la tio n sh ip between measured s o il w ater c o n te n t in the top
21 cm of the s o il p r o f i l e and L-band e m is s iv ity f o r the spring e x p e r i­
ment showing the algo rithm developed from sim ulated r e s u l t s superimposed
on the d a ta . In verted s o il m oisture p r o f i l e s were d e l e te d .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
115
CO r
(O
Z
O
t— 10
Z
LU
h-
Z
o
U ff
cc
JU
f_
(X
2jcn
O
CO.OJ -
SUMMER
O
0.3
0.>4
0.5
0.6
0.7
0.8
L-BRND EMISSIVITY
0 .9
1. 0
FIG. 60. R ela tio n sh ip between measured s o i l w ater co n te n t in th e top
21 cm o f th e s o i l p r o f i l e and L-band e m is s i v ity f o r th e summer e x p e r i­
ment showing the algorithm developed from sim ulated r e s u l t s superimposed
on th e d a t a . Inverted so il m oisture p r o f i l e s were d e le te d .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
116
U
1— in
LU
F—
-1
FALL
0 .3
0 .5
0 .6
0 .7
0.8
L-BAND EMISSIVITY
0 .9
1.0
FIG. 61. R e la tio n s h ip between measured s o il w ater c o n te n t in th e top
21 cm o f th e s o i l p r o f i l e and L-band e m is s iv ity fo r th e f a l l e x p e r i ­
ment showing th e alg o rith m developed from sim ulated r e s u l t s superimposed
on th e d a t a . In verted s o il m o istu re p r o f i l e s were d e l e te d .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
117
WINTER
0.3
O.il
0.5
0.6
0.7
0.8
0.9
1.0
L-BAND EMISSIVITY
FIG. 62. R e la tio n s h ip between measured s o il w ater c o n te n t in th e top
21 cm o f the s o i l p r o f i l e and L-band e m is s i v ity f o r th e w in te r e x p e r i­
ment showing th e algorithm developed from sim ulated r e s u l t s superimposed
on the d a ta . In v erte d s o il m oisture p r o f i l e s were d e le te d .
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
118
rapid drying o f th e s o il p r o f i l e as shown in Fig. 52 (p. 101) f o r the
spring experiment and e s p e c i a ll y in Fig. 53 (p. 102) f o r the summer
experiment.
This phenomenon does not occur during th e f a l l and w in te r
seasons (F ig s. 54 and 55, pp. 103 and 104).
during the w in te r , as expected.
The s o il d ried very slowly
Consequently, more data p o in ts
r e p r e s e n tin g wet s o i l co n d itio n s were p lo t t e d in F ig s. 61 and 62
(pp. 1 16 and 117) f o r th e f a l l and w in te r experim ents.
In v erte d p r o f i l e d ata and th e alg o rith m t o p r e d i c t s o il water
c o n te n t from in v e rte d p r o f i l e s are shown in F ig s. 63 through 66 in
a d d itio n to th e d a ta p rev io u sly p re s e n te d .
In th e se f i g u r e s , in v e rte d
p r o f i l e data are re p re s e n te d by a "+" symbol.
occurred th e day w ater was a p p lie d .
In v erte d p r o f i l e s mainly
O c casio n a lly , however, they a lso
occurred the day a f t e r w ater a p p l ic a t io n which e x p la in s the plus
symbols t h a t c l u s t e r around the r e g u la r s o il m o istu re p r o f i l e s during
the f a l l and w in te r experim ents.
Data p o in ts re p r e s e n tin g in v e rte d
p r o f i l e s e x h ib ite d co n sid e ra b le s c a t t e r during th e sp ring and summer
experiments (F ig s . 63 and 64).
Less s c a t t e r occurred fo r the in v e rte d
p r o f i l e d ata p o in ts shown in Figs. 65 and 66 which r e p re s e n t th e f a l l
and w in te r se a s o n s , r e s p e c t iv e l y .
However, th e s c a t t e r is s t i l l
p r e v a le n t. . The e x a c t cause o f t h i s s c a t t e r is unknown.
Since s o il
m o istu re c o n te n t was a measured v a r i a b l e , th e s c a t t e r can most l i k e l y
be a t t r i b u t e d to measurement e r r o r .
I t i s very obvious t h a t th e in v e rte d p r o f i l e p r e d ic to r equation
developed from sim ulated r e s u l t s does not f i t th e measured d a ta .
The
c r i t e r i a e s t a b l i s h e d to c l a s s i f y an in v e rte d p r o f i l e using L-band
e m is s iv ity is d e f i n i t e l y not a c o n s ta n t value as was assumed in
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
119
U
1—
Lrt
IxJ
Ixl
I—
SPRING
+ INVERTED PROFILES
o REGULAR PROFILES
0.3
0.5
0.6
0 .7
0.8
L-BRND E M I S S I V I T Y
0.9
1. 0
FIG. 63. R ela tio n sh ip between measured s o il w ater co ntent in th e top
21 cm of th e s o il p r o f i l e and L-band e m is s iv ity f o r the spring e x p e r i­
ment in c lu d in g in v e rte d s o il m oisture p r o f i l e s with th e algorithm
developed from sim ulated r e s u l t s superimposed on th e data.
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
120
U
I—
LU
_l
oo
SUMMER
+ INVERTED PROFILES
o REGULAR PROFILES
0.3
0.5
0.6
0 .7
0.8
L-BRND EMISSIVITY
0 .9
1.0
FIG. 64. R ela tio n sh ip between measured s o il w ater co n te n t in th e top
21 cm of th e s o i l p r o f i l e and L-band e m is s iv ity f o r th e summer e x p e r i­
ment in cludin g in v e rte d s o i l m oisture p r o f i l e s with th e algorithm
developed from sim ulated r e s u l t s superimposed on th e d a ta .
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
121
U
L
U
I—
1—
FALL
+ INVERTED PROFILES
o REGULAR PROFILES
0.3
0.5
l
0 .7
0.8
- b r n d 6e m i s s i v i t y
0 .9
1. 0
FIG. 65. R e la tio n s h ip between measured s o il w ater c o n te n t in the top
21 cm o f th e s o i l p r o f i l e and L-band e m is s iv ity f o r th e f a l l experiment
including in v e rte d s o il m o istu re p r o f i l e s with th e alg o rith m developed
from sim ulated r e s u l t s superimposed on th e d a ta .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
122
CD r
CO
CJ
■in
Ll I
O
U=r
cc
LU
I—
CC
2 : 00
o
CD
cu
0
0
WINTER
+ INVERTED PROFILES
0 REGULAR PROFILES
0 .3
O .y
0 .5
0 .6
0 .7
0 .8
L-BRND E M I S S I V I T Y
0 .9
1.0
FIG. 66 . R e la tio n sh ip between measured s o il w ater co ntent in the top
21 cm of th e s o il p r o f i l e and L-band e m is s i v ity f o r the w in ter e x p e r i­
ment in clu din g in v e rte d s o i l m oisture p r o f i l e s with th e algorithm
developed from sim ulated r e s u l t s superimposed on th e d a ta .
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
123
the sim ulated study.
I t wasfound from sim ulated r e s u l t s t h a t a
in L-band e m is s i v ity g r e a t e r
than
0.18 r e p r e s e n te d
change
an in v e rte d p r o f i l e .
The change in e m is s iv ity r e f e r r e d to th e e m is s i v ity one day a f t e r a
r a in minus th e e m is s iv ity on the day o f r a i n .
developed f o r summer c l im a t ic c o n d itio n s o nly.
This c r i t e r i a was
As th e seasons change,
the drying r a t e o f th e s o il a lso changes as shown in Fig. 56 (p. 108).
Thus, th e change in e m is s iv ity from one day to the next is not as
d r a s t i c during th e o th e r seasons as i t i s during the summer.
A fter
examining th e c a l c u la te d change in L-band e m is s i v ity following w ater
a p p l ic a t io n s during each season, i t was found t h a t an in v erted p r o f i l e
could be c l a s s i f i e d i f the change in L-band e m is s iv ity was g r e a t e r
than 0.13 f o r the s p rin g and
fa ll
se a s o n s , g r e a t e r
than 0.18 f o r
th e summer, and g r e a t e r than
0.05
f o r th e w in te r.
However, s o i l w ater
c o n te n t in th e top 21 cm cannot be p r e d ic te d f o r in v e rte d p r o f i l e s
from th e s e d a t a .
Measured s o i l w ater c o n te n t in th e top 21 cm o f th e s o il p r o f i l e
was compared to p r e d ic tio n s o f s o il w ater c o n te n t c a lc u la te d from expec­
ted L-band e m i s s i v i t i e s .
Since the eq u atio n f o r p r e d ic tin g s o il water
co n ten t from in v e rte d p r o f i l e s did not f i t th e measured d a ta , only equa­
tio n s ( I I I - l ) and ( I I I - 2 ) were used to p r e d i c t s o i l water c o n te n t.
One
cm o f w ater was s u b tra c te d from these p r e d ic tio n s to account f o r the
d i f f e r e n c e between th e algo rithm developed from sim ulated r e s u l t s and
th e measured d a t a .
D ifferences between th e measured and p re d ic te d s o il
w ater c o n te n t in th e top 21 cm o f the s o i l p r o f i l e r e s u l t i n g from a p p l i ­
c a tio n o f v arying amounts o f water to s e l e c t e d ly s im e te rs during each o f
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
124
th e fo u r seasons are shown in Figs. 67 through 70.
Soil w ater co n ten t
d ata shown in Fig. 67A r e s u lt e d from 2.31 cm o f water a p p lie d to
ly s im e te r 2C on day 143.
The s o il m oisture p r o f il e on t h i s p a r t i c u l a r
day was c l a s s i f i e d as being in v e rte d .
Since the in v e rte d p r o f i l e
equation did n ot f i t the measured d a t a , th e s o il w ater c o n te n t was
n a t u r a l l y o v e rp re d ic te d by equation ( I I I - l ) .
Very l i t t l e d if f e r e n c e
e x iste d between measured and p r e d ic te d s o il water co n ten t f o r the
f i r s t two days following th e i r r i g a t i o n .
s t e a d i l y in c re a s e d as th e s o il d r ie d .
A fter t h i s , the d if f e r e n c e
Although th e s o i l m o istu re
p r o f i l e in ly s im e te r 3R (F ig . 67B) on th e day o f w ater a p p l ic a t io n was
in v e rte d , th e d if f e r e n c e between c a l c u la te d EQSM f o r X-band and L-band
was only fo u r p e rc e n t.
This s i g n i f i e s t h a t a s u f f i c i e n t q u a n tity o f
w ater was added t o th e s o il p r o f i l e t o wet th e upper l a y e r of s o i l .
Thus, th e p r e d ic te d s o il w ater c o n te n t and measured s o il w ater co n ten t
were n e a rly i d e n t i c a l .
Again, p re d ic te d and measured s o il w ater contents
on th e two days a f t e r i r r i g a t i o n were very c lo se .
As th e s o i l d r i e s ,
one would n a t u r a l l y assume t h a t e m is s i v ity becomes l a r g e r ; however, on
day 170, th e e m is s i v ity c a lc u la te d f o r L-band was le s s than i t was on
day 156.
Soil tem peratures were h o t t e r on day 170 than on day 156 a t the
time s o il m o istu re was measured in t h i s ly s im e te r , e s p e c i a l l y the surface
la y e r.
As a r e s u l t , th e p re d ic te d s o i l w ater content i s much l a r g e r than
i t should be.
This was shown to occu r again in Fig. 68 A on day 226.
Cooler s o i l te m peratu res on day 240 r e s u l t e d in an e m is s iv ity l a r g e r
than i t should be.
Consequently, p r e d ic te d s o il w ater co n ten t was l e s s .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
Reproduced
with permission
(A)
CD
of the copyright owner. Further reproduction prohibited without p erm ission .
PREDICTED
MEASURED
IRRIGATION
o
<u
2
?«0
115
150
155
160
165
170
175
O
O
CCZ
L U co
(B)
cr
* PREDICTED
e MEASURED
f IRRIGATION
CD
CM
?io
145
150
155
TIME
160
(DATS)
165
170
175
FIG. 67. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e and
p r e d i c t e d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model d u rin g
th e s p r in g e x p erim en t f o r (A) 2.31 cm o f w a te r a p p lie d t o l y s i m e t e r 2C and (B) 4 .8 2 cm o f w a te r
a p p l ie d t o l y s i m e t e r 3R.
Reproduced with permission
CD
of the copyright owner. Further reproduction
CR)
PREDICTED
MEASURED
IRRIGATION
to
<\l
LU
?0D
205
2 10
220
215
225
2 30
235
O
O
cc
LU co
(B)
cc
* PREDICTEO
o MEASURED
f IRRIGATION
prohibited without p erm ission.
ru
205
210
2 15
TIME
FIG. 6 8 . Comparison between
p r e d i c t e d s o i l w a te r c o n t e n t
d u rin g th e summer ex p erim en t
ly s im e te r 1L and (B) 2.21 cm
220
(DATS)
2 25
230
235
measured s o i l w a te r c o n t e n t in t h e top 21 cm o f th e s o i l p r o f i l e and
from L-band e m i s s i v i t y c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model
f o r (A) 1.71 cm o f w a te r fo llo w ed by 1.44 cm o f w a te r a p p l ie d to
o f w a te r fo llo w ed by 4 .8 0 cm o f w a te r a p p l ie d to l y s i m e t e r 1R.
Reproduced
with permission
(A)
CD
of the copyright owner. Further reproduction
* PREDICTED
Q MEASURED
f IRRIGATION
CO
O
cu
?95
300
305
310
315
320
325
33 0
335
31 5
(O
O
CC
(B)
L U oo
cr
* PREDICTED
o MEASURED
t IRRIGATION
u>
prohibited without perm ission.
O
CO = f
<\i
3 00
3 05
310
315
TIME
320
325
( D AY S )
330
335
310
315
FIG. 69. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e and
p r e d ic te d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model
d u rin g th e f a l l e x p e rim e n t f o r (A) 1 .6 3 cm o f w a te r fo llo w ed by 6.41 cm o f w a te r a p p l ie d t o
l y s i m e t e r 1R and (B) 6 .3 7 cm o f w a te r fo llo w ed by 3.9 3 cm o f w a te r a p p lie d t o l y s i m e t e r 4R.
Reproduced with permission
1R)
CD
of the copyright owner. Further reproduction
PREDICTED
MEASURED
IRRIGATION
(O
=>*
(_>
D
20
25
30
35
50
55
O
CJ
60
PC
IB)
* PREDICTED
e MEASURED
f IRRIGATION
prohibited without p erm ission .
*
— -Q
'
5
10
15
20
25
30
TIME
35
( DAY S )
UO
«5
50
55
60
FIG. 70.
Comparison between measured s o i l w a te r c o n t e n t in t h e to p 21 cm o f th e s o i l p r o f i l e and
p red ic ted
s o i l w a te r c o n t e n t from L-band e m i s s i v i t y c a l c u l a t e d by th e r a d i a t i v e t r a n s f e r model
d u rin g th e w i n t e r ex p erim en t f o r (A) 1 .58 cm o f w a te r fo llo w ed by 3 .09 cm o f w a te r a p p lie d to
ly sim ete r
1R and (B) 5.17 cm o f w a te r fo llo w ed by 3 .6 6 cm o f w a te r a p p lie d to l y s i m e t e r 3C.
—
oo
129
In t h i s c a s e , i t was n e a rly equal to the measured s o il w ater c o n te n t.
Day 208 showed th e same th in g ; however, i t was not as n o tic e a b le since
the upper value o f e m is s i v ity in the model was lim ited to a value o f
0.89.
The a c tu a l e m is s i v ity c a lc u la te d on t h i s day was 0.91835.
The
e m is s iv ity on day 207 was 0.86800; and on day 212, i t was 0.88910.
An
e m is s iv ity o f 0.91835 would p r e d ic t a s o il w ater c o n ten t o f minus two
cm from equation ( I I I - 2 ) which is im possible.
Measured s o i l w ater
co n te n t and p r e d ic te d s o i l w ater c o n te n t did not compare very well on
any day shown in t h i s f i g u r e .
Both i r r i g a t i o n s were sm all; the f i r s t
one was 1.71 cm follow ed by 1.44 cm.
The same r e s u l t s a r e shown in
Fig. 68 B (p. 126) f o r a 2.21 cm a p p l ic a t io n o f water on day 205.
How­
ev e r, p re d ic te d and measured s o il w ater co n te n t from th e second
a p p lic a tio n o f w ater (4 .8 cm) a re in b e t t e r agreement.
Cooler s o il
tem peratures on days 208 and 240 d e f i n i t e l y confound the r e s u l t s .
Fig. 69A (p. 127) r e p r e s e n ts a 1.63 cm i r r i g a t i o n followed by a 6.41 cm
i r r i g a t i o n during th e f a l l .
The comparison between p re d ic te d and
measured s o il w ater c o n te n t fo llow in g th e f i r s t i r r i g a t i o n was b e t t e r
than t h a t shown in Fig. 68 A ( p . 126) f o r a small i r r i g a t i o n .
Soil water
co n te n t was o v e rp re d ic te d by 2.6 cm on the day o f water a p p l i c a t i o n due
to th e in v e rte d p r o f i l e phenomenon.
On th e day o f the second a p p lic a ­
tio n o f w ater, s o il w ater c o n te n t was underpredicted by approxim ately
one cm.
The s o il m oisture p r o f i l e on t h i s day was a r e g u la r p r o f i l e ;
L-band EQSM was l a r g e r than X-band EQSM.
unknown, p o s s ib ly a measurement e r r o r .
The reason f o r t h i s is
P red icted 'and measured s o il
water c o n te n ts compared f a i r l y well except on days 338 and 345.
L-band
e m is s iv ity was again c a l c u la te d too la rg e which caused s o i l w ater
R ep ro d u ced with p erm ission of the copyright ow ner. Further reproduction prohibited w ithout p erm ission .
130
c o n te n t to be un d erp red icted .
This was a ls o seen in Fig. 70 (p. 128).
The second w ater a p p lic a tio n shown in Fig. 70B (3.66 cm) was somewhat
l a r g e r than the second a p p lic a tio n in F ig. 70A (3.09 cm), but f o r a l l
p r a c t i c a l purposes they were n e a rly a l i k e .
The p o in t o f i n t e r e s t is
t h a t th e re was very l i t t l e d if f e r e n c e between p re d ic te d and measured
s o il water co n te n ts in Fig. 70B; whereas, some d if f e r e n c e e x iste d
between th e two m oisture co ntents in F ig. 70A.
The second a p p l ic a t io n
in Fig. 70A followed a small i r r i g a t i o n (1 .58 cm); th u s , th e s o il was
dry p r i o r to the second i r r i g a t i o n .
In F ig. 70B, the f i r s t i r r i g a t i o n
amount was 5.17 cm which r e s u lt e d in a w e tte r s o il p r o f i l e p r i o r to
th e second a p p l ic a t io n o f w ater.
The comparison between measured s o il
w ater c o n te n t and p re d ic te d s o il water c o n te n t was very good in Fig.
70B f o r both w ater a p p lic a tio n s except on day 59.
Once a g ain , s o il
tem peratures were h o t t e r on t h i s p a r t i c u l a r day; th u s , L-band
e m is s iv ity was c a l c u la te d too sm all.
Consequently, the p re d ic te d s o il
w ater c o n te n t was too la rg e .
Second Layer Algorithm
The r a t i o o f the change in X-band and L-band e m is s i v i t i e s one day
a f t e r th e r a i n event was found to be an e x c e l l e n t e s tim a to r f o r the
amount o f w ater added to the lower p o rtio n o f the s o il p r o f i l e (21 to
150 cm) due to p e r c o la tio n .
This alg o rith m (developed from sim ulated
r e s u l t s ) was shown in g rap hical form in F ig . 46 (p. 80) and was
re p re s e n te d m athem atically by eq uation ( I I I - 4 ) .
The algorithm was
superimposed on p lo t s o f water added to th e 21 to 150 cm la y e r o f the
s o il p r o f i l e versus the r a t i o o f th e one day change in X-band and L-
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
131
band e m i s s i v i t i e s as shown in Figs. 71, 72, 73, and 74 f o r the s p rin g ,
summer, f a l l , and w in te r experim ents, r e s p e c t i v e l y .
The amount o f
water added to t h i s lower s o il la y e r was c a lc u la te d by s u b tr a c tin g the
s o il w ater c o n te n t in th e 21 to 150 cm s o il la y e r p r i o r to applying
w ater to th e s o i l from th e maximum s o i l w ater c o n te n t in t h i s la y e r
th a t occurred a f t e r w ater was a p p lie d .
Table 6 shows the amount of
water added to the lower s o il la y e r in r e l a t i o n to th e amount o f w ater
applied to the s o i l in each o f the ly s im e te r s .
obviously not c o r r e c t .
Some o f these d a ta are
For example, ly s im e te r 1C had 2.21 cm o f water
applied in the s p r in g ; o f t h i s , 1.99 cm o f w ater was added to the lower
la y e r.
For the f i r s t a p p l ic a t io n during th e summer, ly s im e te r 3L had
4.31 cm o f water a p p lie d to the s o i l ; 4.61 cm o f w ater was found to
be added to the 21 to 150 cm s o il la y e r .
Even a f t e r d e l e tin g th e bad
data p o in ts (an X drawn through the p o in t) in Figs. 71 through 74,
c o n s id e ra b le s c a t t e r s t i l l e x i s t e d .
th is.
A number o f f a c t o r s could cause
Soil m oistu re p r o f i l e s p l o t te d in Figs. 52 through 55 (pp. 101
through 104) in d i c a t e t h a t w ater moved through the s o il very ra p id l y .
Thus, a buildup o f d rain a g e w ater in th e bottom o f the ly sim ete rs could
cause th e s o i l w ater c o n te n t in th e 21 to 150 cm s o i l la y e r to be
g r e a t e r than i t a c t u a l l y should be.
Another p o s s i b i l i t y is t h a t the
water followed th e l e a s t path o f r e s i s t a n c e through the s o il p r o f i l e
by flowing down th e access tubes and w a lls o f th e ly s im e te r s .
However,
t h i s is no t l i k e l y to occur f o r an u n s a tu ra te d s o i l .
The amount o f w ater added to th e lower s o i l la y e r was c a lc u la te d
by equation ( I I 1-4) r e g a r d l e s s o f th e poor f i t between th e algorithm
and the measured d a t a .
These d ata a r e shown in Tables 7 through 10 f o r
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
132
SPRING
X BAD DflTfl POINTS
o
tn
u_
u
0.6
0.8
1.0
1.2
1.4
( D E L T A E M I S X ) / ( DEL TA E M I S L )
1.6
1.8
FIG. 71. R e la tio n sh ip between amount of w ater added to the 21 to 150 cm
s o il la y e r in th e measured s o il p r o f i l e and th e r a t i o o f X-band and Lband change in e m i s s i v i t i e s f o r the spring experim ent w ith the algorithm
developed from sim ulated r e s u l t s superimposed on th e d a ta .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
133
SUMMER
BAD ORTA POINTS
X
u.
a. co
cn
CCU)
iu
« 39
U
UJ
LU
'■■■ |
0 .6
1
i
0.8
-
g o
.1
1.0
1.2
..
(d
1.14
( D EL TA E M I S X ) / ( DEL TA E MI S L )
1.6
1.8
FIG. 72. R e la tio n sh ip between amount o f water added to the 21 to 150 cm
s o il la y e r in th e measured s o il p r o f i l e and the r a t i o of X-band and Lband change in e m i s s i v i t i e s f o r the summer experiment with the algorithm
developed from sim ulated r e s u l t s superimposed on the d a ta .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
134
FALL
X
BflO DflTfl POINTS
CD
U_
O
CL
CCLD
UJ
LU
Q
LU
O
0.4
0.6
.
i
0.8
1.0
1.2
1.4
( D E L T A E M I S X ) / ( DEL TA E M I S L )
1.6
1.8
FIG. 73. R e la tio n sh ip between amount of w ater added to th e 21 to 150 cm
so il la y e r in th e measured s o il p r o f i l e and th e r a t i o of X-band and Lband change in e m i s s i v i t i e s f o r th e f a l l experiment with the algorithm
developed from sim ulated r e s u l t s superimposed on the d a ta .
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
135
WINTER
X
BAD DATA POINTS
Q_ CO
cn
u.
o
a
cc
UJ
) ................ '---------------—
0.4
0.6
0.8
1.0
..
i-------------------- 1______
1.2
1.4
( D E L T A E M I S X ) / ( DE LT A E M I S L )
1.6
1. 8
FIG. 74. R e la tio n sh ip between amount o f water added to th e 21 to 150 cm
s o il l a y e r in the measured s o i l p r o f i l e and th e r a t i o of X-band and Lband change in e m i s s i v i t i e s f o r th e w in te r experim ent with th e algo rithm
developed from sim ulated r e s u l t s superimposed on th e d a ta .
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
Reproduced with permission
TABLE 6.
of the copyright owner. Further reproduction
AMOUNT OF WATER ADDED (in cm) TO THE 21 TO 150 CM SOIL LAYER FROM WATER APPLIED (in cm)
TO EACH LYSIMETER DURING THE FOUR SEASONAL EXPERIMENTS
Spring
Second
Application
Lysim­
eter
Water
Applied
1L
2.07
1C
Water
Added
Fall
Summer
First
Application
Second
Application
First
Application
Winter
Second
Application
First
Application
Second
Application
prohibited without p erm ission.
Water
Applied
Water
Added
Water
Applied
Water
Added
Water
Applied
Water
Added
Water
Applied
Water
Added
Water
Applied
Water
Added
Water
Applied
Water
Added
0.03
1.71
1.46
1.44
0.00
2.06
1.40
1.68
0.53
1.66
0.74
2.22
0.31
2.21
1.99
2.00
0.37
2.48
0.00
2.47
1.48
3.99
1.60
1.88
1.01
3.52
1.67
1R
4.56
2.39
2.21
0.54
4.80
0.54
1.63
0.84
6.41
3.60
1.58
0.00
3.09
1.76
2L
1.69
1.44
2.95
1.60
1.81
0.00
3.33
1.21
1.73
0.45
3.24
1.79
1.46
1.15
2C
2.31
0.23
2.62
2.21
2.39
0.00
2.54
1.75
2.49
0.03
2.34
1.68
2.24
0.00
2R
3.36
1.52
2.94
2.15
4.12
0.50
3.23
0.73
4.83
1.10
3.03
1.45
3.28
2.52
3L
1.68
1.56
4.31
4.61
1.71
0.00
6.97
3.21
1.85
0.72
5.32
1.96
1.87
2.05
3C
3.45
2.72
6.12
3.90
3.05
0.00
4.68
3.51
4.00
1.90
5.17
1.66
3.66
0.89
3R
4.82
3.17
3.97
4.59
3.85
2.06
5.63
1.07
5.44
2.45
4.24
1.41
2.99
3.51
4L
1.22
1.10
4.71
3.93
1.81
0.00
9.52
5.11
1.77
1.50
5.22
3.23
1.29
0.38
4C
2.99
1.89
4.72
4.40
1.58
0.64
3.93
3.50
2.61
0.38
5.09
3.06
2.65
2.53
4R
3.88
2.52
7.91
4.93
3.38
0.64
6.37
2.35
3.93
1.97
7.05
3.47
3.22
1.27
u>
o*
137
TABLE 7. COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS
OF WATER ADDED (in cm) TO THE 21 TO 150 CM SOIL
LAYER DURING THE SPRING EXPERIMENT
Water Added (cm) to the Lower
Soil Layer
Lysimeter
Aex/Ae|_
Measured
P redicted
1L
1.5050
0.03
-350.34
1C
1.0900
1.99
- 1.02
1R
1.0180
2.39
0.15
2L
1.6641
1.44
-1050.32
2C
0.9370
0.23
0.16
2R
1.1649
1.52
- 6.68
3L
1.1853
1.56
-9.72
3C
0.7524
2.72
1.16
3R
0.9469
3.17
0.16
4L
1.0591
1.10
-0 .2 3
4C
0.7963
1.89
0.81
4R
0.8900
2.52
0.23
R ep ro d u ced with p erm ission o f th e copyright ow n er. Further reproduction prohibited w ithout perm issron
73
CD
"O
—
5
o
Q.
C
,ission of the copyright owner. Further reproduction
®
3
TABLE 8 .
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS OF WATER ADDED
( i n cm) TO THE 21 TO 150 CM SOIL LAYER DURING THE
SUMMER EXPERIMENT
________F i r s t Water A p p lic a tio n
Second Water A p p lic a tio n ____________
Water Added (cm) t o th e Lower
____________ S o il Layer
L ysim eter
Ae x / A e l
Measured
P r e d ic t e d
Water Added (cm) t o th e Lower
S o il Layer_________
A e x / A e |_
Measured
P r e d ic t e d
prohibited without perm ission.
1L
0.9146
1.46
0 .1 8
1.3960
0.00
-1 37.83
1C
0.8055
0 .4 0
0 .7 4
1.1371
0.00
- 3 .7 4
1R
0.8275
0 .5 4
0.57
0.9764
0.54
0 .1 8
2L
0.7742
1.60
0 .9 9
1.3908
0.00
-1 3 1 .1 6
2C
0.8070
2.21
0 .7 3
1.1652
0.00
-6 .7 2
2R
0.5432
2.15
5.82
0.9346
0 .5 0
0.1 6
3L
0.7634
4.61
1.07
1.0161
0.00
0.15
3C
0.6782
3.90
1.78
0.9085
0.00
0 .1 9
3R
0.8008
4.59
0.77
1.0903
2.06
- 1 .0 3
4L
0.7224
3 .9 3
1.40
0.9251
0.00
0 .16
4C
0.7251
4 .4 0
1.38
1.1899
0.6 4
-1 0 .5 3
4R
0.6719
4 .9 3
1.85
1.0591
0.6 4
- 0 .2 3
CO
00
Reproduced with permission
TABLE 9.
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS OF WATER ADDED
( i n cm) TO THE 21 TO 150 CM SOIL LAYER DURING THE
FALL EXPERIMENT
of the copyright owner. Further reproduction
F i r s t Water A p p lic a tio n
Second Water A p p lic a tio n
Water Added (cm) to th e Lower
S o il Layer
Water Added (cm) to th e Lower
S o il Layer
prohibited without p erm ission.
Lysim eter
Acx/A cl
Measured
P r e d ic t e d
Aex/A el
Measured
P r e d ic te d
1L
1.1956
1.4 0
-1 1 .6 0
1.1655
0 .5 3
- 6 .7 6
1C
1.0075
1.48
0 .1 8
0.8153
1 .6 0
0.66
1R
1.0 1 2 0
0 .8 4
0.17
0.8908
3 .60
0 .2 3
2L
1.1965
1.21
-1 6 .7 7
1.0333
0.45
0.07
2C
1.0014
1.74
0 .1 8
0.8 6 6 8
0.03
0.33
2R
0.7320
0.72
1.32
0.6990
1 .1 0
1.59
3L
0.7898
3.21
0.86
0.8571
0.7 2
0 .38
3C
0.8672
3.51
0 .3 3
0.8452
1.90
0.45
3R
1.0312
1.07
0.08
0.9006
2.45
0.20
4L
0.8630
5.11
0.35
0.7386
1.50
1.27
4C
0.9245
3.50
0.1 6
0.8554
0 .3 8
0 .3 9
4R
0.8056
2.35
0 .7 4
0.7992
1.97
0 .7 9
P
O
CD
"O
o
Q.
C
ion of the copyright owner. Further reproduction
?
i.
«
TABLE 10.
COMPARISON BETWEEN MEASURED AND PREDICTED AMOUNTS OF WATER ADDED
( i n cm) TO THE 21 TO 150 CM SOIL LAYER DURING THE
WINTER EXPERIMENT
F i r s t Water A p p lic a tio n
Second Water A p p lic a tio n
Water Added (cm) t o th e Lower
S o il Layer
Water Added (cm) t o th e Lower
S o il Layer
prohibited without p erm ission .
L ysim eter
Aex/AeL
Measured
P r e d ic t e d
AEx/A cl
Measured
P r e d ic te d
1L
0.8667
0.74
0 .3 3
0.7541
0.31
1.15
1C
0.7743
1.01
0 .9 9
0.5353
1.67
6 .4 2
1R
0.9880
0 .0 0
0 .1 9
0.6320
1.76
2.39
2L
0.7342
1.79
1.31
0.8087
1.15
0.71
2C
0.8186
1 .6 8
0 .6 4
0.6613
0 .0 0
1.96
2R
0.6204
1.45
2.61
0.6831
2.52
1.74
3L
0.7378
1.96
1.28
0.7017
2.05
1.57
3C
0.7573
1 .6 6
1 .1 2
0.6469
0 .8 9
2.15
3R
0.7312
1.41
1.33
0.7185
3.51
1 .4 3
4L
0.5363
3.23
6 .34
0.8158
0 .3 8
0 .6 6
4C
0.7099
3 .0 6
1 .50
0.8161
2.53
0 .6 6
4R
0.7520
3.47
1 .16
0.8382
1.27
0.5 0
141
th e f o u r seasons.
Comparisons between measured and p red ic ted amounts
of added w a te r t o th e lower s o il la y e r d e f i n i t e l y in d ic a te a poor f i t
with th e measured d a ta .
However, i t appears t h a t th e algorithm may
be s e a s o n a lly dependent.
This was in d ic a te d by th e d if f e r e n c e in drying
r a t e s o f th e s o i l f o r th e fo u r seasons as shown in Fig. 56 (p. 108).
The range o f v alu es f o r th e computed r a t i o o f th e change in X-band and
L-band e m i s s i v i t i e s given in Tables 7 through 10 (pp. 137 through 140)
a ls o in d i c a te t h i s .
The r a t i o v a rie d from 0.75 t o 1.55, 0.54 to 1.40,
0.70 t o 1 .20 , and 0.53 t o 0.99 during th e s p r in g , summer, f a l l , and
w in te r, r e s p e c t iv e l y .
Even though i t appears t h i s algorithm w ill
change with each seaso n, th e s c a t t e r in th e s e d a ta p r o h ib i ts any
f u r t h e r development.
The a lg o rith m s developed t o p r e d i c t th e s o il w ater c o n ten t in th e
top 21 cm of t h e s o i l p r o f i l e and to e s tim a te th e amount o f w ater added
to th e 21 to 150 cm s o il la y e r have not been adeq u a tely t e s t e d .
The
p re d ic te d and measured s o i l m oisture in th e top 21 cm compared favorably
on many o ccasions but d id n o t compare well on o t h e r s .
There may a ls o
be some doubt as to th e accuracy of e m i s s i v i t i e s c a l c u la te d by the
r a d i a t i v e t r a n s f e r model sin c e i t has not been e x te n s iv e ly t e s t e d .
T h e re fo re , th e only way to t e s t t h i s p r e d ic tio n model is to measure th e
microwave emission as well as s o il m oisture and s o i l tem perature with
time f o r a number o f d i f f e r e n t s iz e r a in ev en ts.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
142
Empirical Approach to Estim ating Em issivity
Since th e r a d i a t i v e t r a n s f e r model appeared to be s e n s i t i v e to
s o il tem perature changes, an em pirical approach d escribed by Blanchard
(1979) was used to e stim ate X-band and L-band e m i s s i v i t i e s .
P e n e tra tio n
depths f o r X-.band and L-band rad io m eters were superimposed on a time s e ­
r i e s p l o t o f measured s o il m oisture p r o f i l e s as shown in Fig. 75.
The
s a tu r a t e d m o istu re co n ten t f o r th e sandy loam s o il in the ly s im e te rs
was assumed to be approximately 40 p e rc e n t by volume.
At s a t u r a t i o n ,
X-band was assumed to p e n e tr a te th e s o i l 0 .5 cm; L-band p e n e t r a ti o n
depth was taken as 5 cm.
On the dry end, X-band p e n e tr a tio n depth was
assumed to be 2.5 cm a t a m oisture c o n te n t o f 2.5 p erce n t by volume;
whereas, L-band depth of p e n e tr a tio n was s e t a t 20 cm f o r a mean
m oisture c o n te n t o f e i g h t p e rc e n t.
This was much more r e a l i s t i c than
the p e n e t r a ti o n depths f o r X-band and L-band as c a lc u la te d by the
r a d i a t i v e t r a n s f e r model.
To c a l c u l a t e e m is s iv ity , th e mean s o il m oisture co n ten t was d e t e r ­
mined f o r th e l a y e r o f s o il sensed by th e p a r t i c u l a r radiom eter on the
day in q u e s tio n .
E m issiv ity was then determined from an em pirical
r e l a t i o n s h i p between e m is s iv ity and s o i l m o istu re co ntent (Blanchard,
1979) f o r X-band and L-band (F ig . 7 6 ).
This r e l a t i o n s h i p was determined
from r e s u l t s r e p o rte d by Schmugge e t a l . (1974, 1976) and by Newton
(1977).
X-band e m is s iv ity and L-band e m is s i v ity was determined f o r
s o il m o istu re c o n d itio n s produced by 13 d i f f e r e n t amounts o f a p p lie d
w ater ran ging from 1.22 cm to 9.52 cm.
F ig. 77 shows the r e l a t i o n s h i p
between s o i l w ater c o n te n t in the top 21 cm o f th e s o il p r o f i l e and
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143
M OISTURE CONTENT
{/ BY V O L U M E )
X-BfiNO
L-BflND
cn
05
o
m
o
x
+
a
*
-
3QQ
301
302
304
3Q5
307
n
f
X-3RN0
- L-BflND» /
t!--
Ch*
FIG. 75. Assumed X-band and L-band p e n e tr a tio n depths (s o lid lin e s )
used with em pirical approach to estim ate e m is s i v ity compared to
p e n e tr a tio n d ep th s c a lc u la te d by th e r a d i a t i v e t r a n s f e r model f o r
X-band ( s h o r t dashes) and L-band (long d a s h e s ).
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144
CD
o
o
cn•
o
in
co
o
o
CO
■
o
> o
cn
COo
Z o
L
U
in
co
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o
CO
o
in
in
•
o
o
in
•
o 0
10
SOIL MOISTURE
20
30
i X BY V O L U M E )
FIG. 76. R e la tio n sh ip between e m is s i v ity and s o il m oisture c o n te n t f o r
X-band and L-band ra d io m e te rs, a f t e r Blanchard (1979).
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145
R = 0.9886
U
L'J
_1
0.5
0. 6
0.7
0.8
L-BRND E M I S S I V I T Y
0.9
1.0
FIG. 77. R e la tio n s h ip between measured s o i l w ater c o n te n t in the top
21 cm o f th e s o il p r o f i l e and L-band e m is s iv ity as determined by the
em pirical approach.
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146
L-band e m is s iv ity .
Measured s o il m oistu re p r o f i l e d ata (normal and
in v e rte d ) from a l l f o u r seasons were used to develop t h i s r e l a t i o n s h i p .
p
The b e s t f i t equ ation (R = 0.9886) through th e s e d ata p o in ts as
determined by l e a s t
squares l i n e a r re g re s s io n was:
Soil Water Content = -16.81836 eL + 16.46503
(V-l)
where Soil Water Content is th e s o il w ater c o n te n t (in cm) in th e top
21 cm o f th e s o il p r o f i l e and
is th e L-band e m is s i v ity (dimension-
l e s s ) determined by th e em pirical approach.
This equation was then used to p r e d ic t s o i l w ater c o n te n t in the
top 21 cm o f th e s o i l p r o f i l e f o r th e same s o i l m o istu re co n d itio n s
t h a t were s e le c te d to t e s t equations ( I I I - l ) and ( I I 1-2) (F ig s. 67
through 70, pp. 125 through 128).
P red icted s o il m oisture co n te n t along
with the measured s o il m oistu re con ten t i s shown in Figs. 78 through 81.
S oil w ater c o n t e n t on th e day of w ater a p p l i c a t i o n in F ig. 78A i s o v er­
p re d ic te d by only 0 .2 cm as opposed to 1.9 cm by th e o th e r algorithm
shown in Fig. 67A (p . 125).
The maximum d i f f e r e n c e between p red ic ted
and measured s o il m o istu re c o n ten t from any of th e s e f ig u r e s was 0.35
cm.
As a whole, t h i s equation p re d ic te d th e s o i l w ater c o n ten t in th e
top 21 cm o f th e s o i l p r o f i l e re g a r d le s s o f th e i r r i g a t i o n amount and
whether o r n o t th e s o il m oisture p r o f i l e was in v e rte d .
The 13 events used to develop equation (V -l) were a ls o used to
develop a r e l a t i o n s h i p between th e amount o f w ater added to the 21 to
150 cm s o il l a y e r and th e r a t i o of th e change in X-band and L-band
e m is s iv ity .
These d ata a re shown in Fig. 82.
Once a g a in , t h i s proved
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Reproduced
with permission
(A)
CD
of the copyright owner. Further reproduction
PREDICTED
MEASURED
IRRIGATION
U>
O
CM
150
155
160
165
170
175
D
(_>
CO
(B)
CE
* PREOICTED
a MEASUREP
f IRRIGATION
ta
prohibited without perm ission.
Q
CO
150
TIME
160
165
170
175
( D AY S )
FIG. 78. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e and
p r e d ic te d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y e s ti m a t e d by t h e e m p iric a l approach d u rin g th e
s p r in g ex p erim en t f o r (A) 2.31 cm o f w a te r a p p lie d t o l y s i m e t e r 2C and (B) 4 .8 2 cm o f w a te r a p p lie d
t o ly s i m e t e r 3R.
^
'"J
Reproduced with permission
CO)
of the copyright owner. Further reproduction
PREDICTED
MERSURED
IRRIGATION
</>
O
CM
Ui
Woo
205
220
2)0
225
230
235
Q
(_>
0C
CO
(B)
* PREDICTED
o MEflSUREO
f IRRIGHT ION
(X
prohibited without p erm ission.
ED
CO a*
205
210
215
TIME
220
( D AY S )
225
2 30
23 5
FIG. 79. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e and
p r e d i c t e d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y e s ti m a t e d by t h e e m p iric a l approach d u rin g th e
summer ex p e rim e n t f o r (A) 1.71 cm o f w a te r fo llo w e d by 1 .4 4 cm o f w a te r a p p l ie d to l y s i m e t e r 1L and
(B) 2.21 cm o f w a te r fo llo w ed by 4 .8 0 cm o f w a te r a p p lie d t o l y s i m e t e r 1R.
^
oo
Reproduced with permission
of the copyright owner. Further reproduction
CO
im
(0
* PREDICTED
e MERSURED
f IRRIGATION
o
<\l
300
3 05
3 10
3 )5
320
325
330
335
3*10
DC
IQ)
cr
* PREDICTED
e MEASURED
f IRRIGATION
ID
prohibited without p erm ission
ru
300
305
310
3 15
T IIM E
32 0
3 25
( DAYS)
3 30
3 35
FIG. 80. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f t h e s o i l p r o f i l e and
p r e d i c t e d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y e s tim a te d by th e e m p iric a l approach d u rin g th e
f a l l ex p e rim e n t f o r (A) 1.63 cm o f w a te r fo llo w e d by 6.41 cm o f w a te r a p p lie d t o l y s i m e t e r 1R and
(B) 6.3 7 cm o f w a te r fo llo w ed by 3.93 cm o f w a te r a p p l ie d t o l y s i m e t e r 4R.
—■
S
R e p ro d u c e d
with
p e r m is s io n
CD
Ifl)
PREDICTED
MEASURED
of the
IRRIGATION
c o p y rig h t o w n e r .
o
<\i
LU
L— o,
F u rth e r
O
(_>
r e p ro d u c tio n
LU co
20
25
30
35
U5
50
55
60
(B i
* PREDICTED
o MEASURED
f IRRIGATION
(X
(O
p r o h ib ite d
O
CO =r
w ith o u t p e r m i s s i o n .
c\i
20
25
30
TIME
35
( D AY S )
yo
«5
50
55
60
FIG. 81. Comparison between measured s o i l w a te r c o n t e n t in th e to p 21 cm o f th e s o i l p r o f i l e and
p r e d i c t e d s o i l w a te r c o n t e n t from L-band e m i s s i v i t y e s ti m a t e d by t h e e m p ir ic a l approach d u r in g th e
w in t e r ex p erim en t f o r (A) 1 .5 8 cm o f w a te r fo llo w e d by 3 .0 9 cm o f w a te r a p p lie d t o l y s i m e t e r 1R
and (B) 5.17 cm o f w ater fo llo w ed by 3.6 6 cm o f w a te r a p p lie d t o l y s i m e t e r 3C.
151
LU
L i.
0(0
oc
a.
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io
u.
o
o
CC 3*
0
o
Q_
o
CC
LU
O
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o
o
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IS
o
0. 0
0.4
0.8
1.2
1.6
2.0
2.4
( D E L T A E M I S X ) / ( DELTA E M I S L )
2.8
3.2
FIG. 82. R e la tio n s h ip between amount of w ater added to th e 21 t o 150 cm
s o il la y e r and th e r a t i o of X-band and L-band change in e m i s s i v i t i e s
determined by th e em pirical approach of estim a tin g e m is s i v ity .
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152
h o peless.
Thus, one o f two th in g s now becomes obvious.
E ith e r the
measured s o i l w ater co n te n t i s in e r ro r o r the in h e re n t v a r i a b i l i t y in
n a tu ra l s o il i s too g r e a t to develop such an alg o rith m .
One must
remember t h a t th e alg orith m was developed f o r a homogeneous, is o tr o p ic
s o i l ; something t h a t does not e x i s t in i t s n a tu ra l s t a t e .
E rrors in
measured s o i l m oisture should have been minimal s in c e gamma probe
measurements o f s o il m o isture was within one p e rc e n t by volume of
g ra v im e tric sampling over a m oisture c o n te n t range o f 16 t o 29 percent
by volume.
Soil m oisture co n te n t in the s o i l p r o f i l e was u s u a lly
w ithin t h i s range except in the n e a r-s u rfa c e la y e r .
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153
CHAPTER VI
SUMMARY AND CONCLUSIONS
Summary
Soil m oisture p r o f i l e s were sim ulated f o r a h y pothetical loam -like
s o il with a w ater and heat balance model.
Output o f s o il water c o n te n t
and s o i l tem perature was used as in p u t to a r a d i a t i v e t r a n s f e r model to
sim ulate X-band and L-band radiom eter response to the e x i s t in g condi­
ti o n s .
Time s e r i e s p l o t s o f s o il m oisture p r o f i l e s were presen ted f o r
various r a i n f a l l amounts.
X-band and L-band response to some of th e se
s o il m oisture c o n d itio n s were shown in terms of p e n e tra tio n depth and
p r o f i l e s o f em itted energy.
I t was shown t h a t X-band was s e n s i t i v e to
s o il m oistu re in th e top one to two cm o f s o i l ; whereas, L-band
responded to s o i l m o istu re a t g r e a t e r depths.
L-band was shown to be
p a r t i c u l a r l y s e n s i t i v e to s o il m oisture in th e top 21 cm of the
h y p o th e tica l s o i l p r o f i l e .
An a lg o rith m was developed to e s tim a te the s o il water c o n te n t in
the top 21 cm o f th e s o il p r o f i l e from L-band e m is s iv ity .
I t was v a lid
over a range o f m o istu re co n ten ts from n e a r - s a t u r a t i o n to approxim ately
the w ilt in g p o in t .
I t a ls o has a f e a t u r e to c l a s s i f y in v e rted s o il
m oisture p r o f i l e s t h a t r e s u l t from small r a i n s and p r e d ic t the s o il
w ater c o n te n t when in v e rte d p r o f i l e s occur.
D aily e stim ates o f s o il
m oisture in th e top 21 cm of the s o il p r o f i l e a r e f e a s i b l e with t h i s
algorithm .
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154
E m issivity versus time p lo t s f o r v arious r a i n f a l l events in d ic a te d
th a t d a ily measurements were n ecessary in o rd e r to observe th e ra p id ly
changing s o il m oisture c o n d itio n s follow ing r a i n f a l l .
F u rth er evidence
fo r the need o f d a i l y measurements was presented in th e development o f
the algorithm to e s tim a te th e amount o f w ater added t o th e lower s o il
p r o f i l e (21 to 150 cm d e p th ).
Water added to the lower s o il p r o f i l e
was estim ated from a r a t i o o f th e change in X-band e m is s iv ity and Lband e m is s iv ity one day a f t e r th e ev en t.
An attem pt was made to v e r if y th e se alg o rith m s using measured s o il
moisture data and s o il tem perature d ata f o r a sandy loam s o il contained
in ly s im e te rs .
A two-probe d e n s ity gauge was used to measure s o il
water c o n te n t.
Soil tem perature was measured with thermocouples.
The
r a d i a t i v e t r a n s f e r model used in th e sim ulated study was used to
c a l c u la te e m i s s i v i t i e s t h a t would be expected from th e se measured
co n ditio ns f o r X-band and L-band.
The algo rithm developed from sim ulated r e s u l t s to p r e d i c t so il
water co n ten t in th e top 21 cm o f th e s o il p r o f i l e was f i t t e d to the
measured d a ta .
U n fo rtu n a te ly , th e eq uation developed to e s tim a te s o il
water co n ten t f o r in v e rte d s o il m o isture p r o f i l e s d id not f i t the
measured d a ta .
There was so much s c a t t e r in th e in v e rte d p r o f i l e data
t h a t i t was hopeless to pursue f u r t h e r development o f t h a t eq uatio n.
However, i t was found t h a t th e value used to c l a s s i f y an in v e rte d
p r o f i l e from the change in L-band e m is s iv ity changed with th e seasons
of the y e a r due to the change in dry in g r a t e o f a s o i l during the
d i f f e r e n t s e a s o n s .'
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155
P r e d ic tio n s o f s o il w ater c o n te n t in the top 21 cm o f the s o i l
p r o f i l e met w ith lim ite d r e s u l t s .
Since the in v e rted p r o f i l e equation
d id not f i t th e d a t a , s o il w ater c o n te n ts were o v erp red icted when
in v e rte d p r o f i l e s occurred.
Soil w ater co n te n t was a ls o o v e rp re d ic te d
follow ing small i r r i g a t i o n s (one and two cm).
O ccasio n ally , the
alg o rith m did a f a i r to good job o f p r e d ic tin g s o il w ater c o n te n t.
E m is s iv itie s c a l c u la te d by th e r a d i a t i v e t r a n s f e r model r a is e d some
doubt as to w hether or not they were c o r r e c t sin c e the model appeared
to be very s e n s i t i v e to s o il tem perature changes.
Since e m is s iv ity
i s th e d r iv in g v a r ia b le in th e se p r e d i c t o r e q u a tio n s, the d is c re p a n c ie s
between measured and p re d ic te d s o i l m oisture c o n ten t may be due to
in c o rre c tly calcu la ted e m is siv itie s .
The alg o rith m to e s tim a te w ater added to th e 21 to 150 cm s o il
la y e r did not f i t the measured d a ta e i t h e r .
Again, the d a ta s c a t t e r
p ro h ib ite d f u r t h e r development o f t h i s a lg o rith m .
However, i t was
found t h a t time o f y e a r would a ls o have an e f f e c t on t h i s alg orith m
s in c e th e r a t i o of th e change in X-band and L-band e m i s s i v i t i e s one
day a f t e r the r a i n was used as th e d r iv in g v a r ia b le .
Time o f y e a r has
a d e f i n i t e e f f e c t on th e drying o f a s o i l .
Since th e r a d i a t i v e t r a n s f e r model appeared to be s e n s i t i v e to
changes in s o i l tem p eratu re, an em pirical approach was used to e s tim a te
X-band and L-band e m i s s i v i t i e s .
An equ atio n was developed from t h i s
technique to p r e d i c t s o i l w ater c o n te n t in th e top 21 cm of the s o il
p r o f i l e from L-band e m is s iv ity c a l c u la te d by th e em pirical approach.
P r e d ic tio n s o f s o i l w ater c o n te n t w ith t h i s equation compared very
fav o rab ly w ith measured s o i l w ater c o n te n t r e g a r d le s s o f th e amount
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
156
of w ater ap p lie d and whether or n o t in v e rte d so il m o istu re p r o f i l e s
occurred.
Development o f an equation t o e s tim a te th e amount o f w ater added
to th e lower s o il p r o f i l e w ith th e em pirical approach a ls o f a i l e d due
to d a ta s c a t t e r .
Conclusions
From th e sim ulated r e s u l t s , i t is concluded t h a t :
1.
Soil w ater c o n te n t in th e top 21 cm of a s o il p r o f i l e can be
p re d ic te d from L-band e m is s i v ity .
In v erte d s o i l m o istu re p r o f i l e s can
be c l a s s i f i e d by using a one day change in L-band e m is s iv ity follow ing
the r a i n f a l l event.
2.
Amount o f w ater added to th e 21 t o 150 cm s o i l l a y e r due t o
p e rc o la tio n can be p re d ic te d from a r a t i o o f a one day change in X-band
and L-band e m is s iv ity a f t e r th e r a i n event.
3.
A comprehensive model was developed t o p r e d ic t s o i l m oistu re
in two la y e r s o f th e r o o t zone.
4.
Microwave measurements must be made d a ily in o rd e r to e s tim a te
th e s o il w ater c o n te n t in th e upper 21 cm o f th e s o il p r o f i l e w ith any
degree o f accuracy due to' th e rap id change in e m is s iv ity follow ing
r a i n f a l l ev en ts.
Conclusions drawn from th e experimental study were:
1.
The c r i t e r i a e s ta b l is h e d t o c l a s s i f y in verted s o il m oisture
p r o f il e s was found to be s e a s o n a lly dependent due t o th e d if f e r e n c e s
in drying r a t e o f a s o il w ith time o f y e a r.
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157
2.
The second la y e r algorithm showed seasonal dependence since
i t was based on a r a t i o of th e change in X-band and L-band e m is siv ity .
3.
P redicted s o il w ater co n ten t in th e top 21 cm of th e s o il
p r o f i l e produced li m it e d r e s u l t s .
4.
P re d ic tio n s with th e second la y e r alg orithm were poor due
to th e d a ta s c a t t e r .
5.
P red icted s o i l w ater content in th e top 21 cm of th e s o il
p r o f i l e from e m p ir ic a lly determined L-band e m i s s i v i t i e s compared
favo rably with measured s o il m oisture re g a rd le s s o f in v e rte d s o il
m oisture p r o f i l e s o r i r r i g a t i o n amount.
Recommendations
The algorithm s in t h i s model have not been ad equately t e s t e d
sin ce actual microwave measurements were not made.
Thus, a program
should be i n i t i a t e d t o measure th e microwave em ission as well a s the
s o il
w ater c o n ten t and s o il tem perature f o r a number o f d i f f e r e n t s iz e
r a in ev en ts.
The experiment should be repeated on d i f f e r e n t
s o il types
and layered s o i l s to determine the li m i t a t i o n s of th e model.
I f th e se alg orithm s work w ith measured d a ta , an evaporation
algorithm should be developed t o estim ate ev ap oration from X-band or
p o ssib ly C-band e m is s i v i t y .
s o il
As a r e s u l t , day t o day p r e d ic tio n of
w ater co n te n t would be f e a s i b l e f o r a 1.5 m p r o f i l e .
The two-probe d e n s it y gauge is by f a r the most a c c u ra te means of
determining s o i l w ater co n te n t o f a l l th e i n d i r e c t methods.
However,
when ta k in g measurements c lo se to the s o il s u rfa c e as is re q u ire d in
microwave s t u d i e s , th e gamma beam should be c o llim a te d as suggested by
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158
DeVries (1969).
This w ill improve the r e s o lu tio n o f th e instrum ent
when taking measurements c l o s e to th e s o il s u r fa c e .
I f c o llim a tio n
of the gamma beam i s n o t u sed , then g rav im etric sampling of th e top
four cm of the s o il is n ecessary.
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159
REFERENCES
1 Aase, J . K., J. R. Wight, and F. H. Siddoway. 1973. Estimating
s o il water co n te n t on n a tiv e rangeland. Agric. M eteorol. 12(2):185191.
2 B aier, W., and G. W. Robertson. 1966. A new v e r s a t i l e s o il
moisture budget. Can. J . P la n t S c i. 4 6 (3 ):299-315.
3
Blanchard, B. J .
1972. Measurements from a i r c r a f t to c h a r a c te r i z e
w atersheds. _Itk A g ric u ltu re and F o restry Programs. Vol. V, pp. 118-1 to
118-4. Fourth Annual Earth Resources Program Review, Houston,
Texas.
4
Blanchard, B. J .
1979. A remote sensing approach to s o i l moisture
modeling. _In: Proceedings o f Workshop on Remote Sensing o f Snow and
Soil Moisture by Nuclear te c h n iq u e s , pp. 191-201. World M eteorological
O rganization. Voss, Norway.
5 Blanchard, B. J . , and W. Bausch. 1979. A conceptual s o i l m oisture
model. Paper presented a t the Spring Meeting o f the AGU, Washington,
D. C.
6 Blinn, J . C., I l l , and J . G. Quade. 1972.
Microwave p r o p e r tie s
o f geological m a te r i a l s :
S tudies o f p e n e tra tio n depth
and m oisture
e f f e c t s . Jrn U n iv ersity Programs. Vol. I I , pp. 53-1 to 53-12.
Fourth
Annual Earth Resources Program Review, Manned S p a c e c ra ft C enter,
Houston, Texas.
7
Bordovsky, J . P.
1978. P re d ic tin g farm machinery o p e ra tio n time
with a s o il m o isture model. M. S. T h esis, Texas A&M U n iv e r s ity ,
College S t a t io n , Texas. 166pp.
8 Campbell S c i e n t i f i c , Inc.
re c o rd e r. Logan, Utah.
O p e ra to r's manual f o r CR5 d i g i t a l
9 C ih la r , J . , and F. T. Ulaby. 1975. Microwave remote sen sing o f
s o il w ater c o n te n t. RSL Technical Report
264-6. The U n iv e rs ity o f
Kansas Center f o r Research, I n c . , Lawrence, Kansas. 183pp.
10 Clapp, R. B ., and G. M. Hornberger. 1978.
Empirical equ ations
fo r some s o il h y d ra u lic p r o p e r t i e s . Water Resour. Res. 14(4):601-604.
11 Dawdy, D. R ., and J . M. Bergmann. 1969. E ffe c t o f r a i n f a l l
v a r i a b i l i t y on streamflow s im u la tio n . Water Resour. Res. 5:958-966.
12 DeVries, J . T969. In s i t u determ in atio n o f phy sical p r o p e r ti e s
of th e s u rfa c e la y e r o f f i e l d s o i l s . Soil S ci. Soc. Amer. Proc. 33(3):
349-353.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
160
13 F reeze, R. A. 1969. The mechanism o f n a tu ra l groundwater recharge
and d isc h a rg e . 1 . One-dimensional v e r t i c a l , unsteady, u n satu rated
flow above a rechargin g or d is c h a rg in g ground-water flow system.
Water Resour. Res. 5 (1 ):15 3-171 .
14 Gardner, H. R ., and W. R. Gardner. 1969. R elation o f w ater
a p p lic a tio n to evaporation and s to ra g e o f s o il w ater. Soil S ci. Soc.
Amer. Proc. 33:192-196.
15 Gardner, W. H. 1965. Water c o n te n t. In: Methods o f Soil
A n aly sis, pp. 82-127. Agronomy Monograph No. 9. Amer. Soc. o f Agron.
16 Gumbs, F. A ., and L. Byam. 1976. P re d ic tio n of s o il water co n te n t
changes in Pangola g rass p a s tu r e s . Trop. Agric. 5 3 (l):3 1 -4 0 .
17 Gurr, C. G. 1962. Use o f gamma rays in measuring w ater c o n ten t
and p e rm e a b ility in u n s a tu ra te d columns o f s o i l . Soil S c i. 94:224-229.
18 Hanks, R. J . , A. K lute, and E. B r e s le r . 1969. A numeric method
f o r e s tim a tin g i n f i l t r a t i o n , r e d i s t r i b u t i o n , drainag e and evaporation
o f w ater from s o i l . Water Resour. Res. 5 ( 5 ) :1064-1069.
19 H ile r, E. A. 1969. Q u a n tita tiv e e v a lu a tio n o f crop drainage
req uirem en ts. TRANSACTIONS o f th e ASAE 1 2 ( 4 ) :499-505.
20 H i l l e l , D. 1975. Sim ulation o f ev ap oratio n from bare s o il under
steady and d i r u n a l l y f l u c t u a t i n g e v a p o r a tiv i ty . Soil S ci. 120(3):
230-237.
21 H i l l e l , D., and C. H. M. van Bavel. 1976. Simulation of p r o f i l e
w ater s to ra g e as r e l a t e d to s o il h y d rau lic p r o p e r ti e s . Soil S c i. Soc.
Amer. J. 4 0 ( 6 ) :807-815.
22 H i l l e l , D.» and H. Talpaz. 1977. Simulation of s o il w ater
dynamics in layered s o i l s . Soil Sci. 123(1):54-62.
23 IBM C orporation. 1975. Continuous system modeling program I I I
(CSMP I I I ) program re fe r e n c e manual, f o u r th e d i t i o n , SHI9-7001-3.
Data P rocessing D iv isio n , IBM, 1133 W estchester Ave., White P l a i n s , •
New York 10604.
24 Idso, S. B . , T. J . Schmugge, R. D. Jackson, and R. J . Reginato.
1975. The u t i l i t y of s u rfa c e tem perature measurements f o r th e remote
sensing of s o i l w ater s t a t u s . Journal o f th e Geophysical Research
80:3044-3049.
25 Idso, S. B . , R. D. Jackson, and R. J , Reginato. 1976. Compensat­
ing f o r environmental v a r i a b i l i t y in. th e thermal i n e r t i a approach to
remote sensing- o f s o il m o istu re. Journal o f Applied Meteorology 15:
811-817.
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
161
26 Jackson, R. D. 1964. Water vapor d i f f u s io n in r e l a t i v e l y dry s o i l :
I I I . S te a d y - s ta te experim ents. Soil S ci. Soc. Amer. Proc. 28:467470.
27 Jackson, R. D. 1972. On th e c a l c u la tio n o f h y d rau lic c o n d u c tiv ity .
Soil S ci. Soc. Amer. Proc. 36:380-382.
28 Jensen, M. E ., J . L. Wright, and B. J . P r a t t . 1971.
s o il m oisture d e p le tio n from c lim a te , crop and s o i l d a ta .
of th e ASAE 14(5):954-959.
Estimating
TRANSACTIONS
29 Moore, R. J . , L. J . C h astan t, I . J. B o rcello , J . Stevenson, and
F. T. Ulaby. 1975. Microwave remote s e n s o rs. In_:
R. G. Reeves (ed .)
Manual o f Remote S ensing, Vol. I , pp. 399-537. Am.Soc. o f Photogratranetry.
30
Newton, R. W. 1977. Microwave remote sensing and i t s a p p lic a tio n
to s o il m oisture d e t e c t i o n . Technical Report RSC-81. Remote Sensing
Center, Texas A&M U n iv e r s ity , College S t a t i o n , Texas. 500pp.
31 N ielsen , D. R ., J . W. Biggar, and K. T. Erb. 1973. S p a tia l
v a r i a b i l i t y o f f i e l d measured s o il w ater p r o p e r t i e s . H ilg a rd ia 42(7):
215-258.
32
Penman, H. L. 1948. Natural evaporation from
s o i l , and g r a s s . Proc. Roy. Soc. 193:120-146.
open w ater, bare
33
P e te r s , D. B. 1965. Water a v a i l a b i l i t y . _l£L:
Methods o f Soil
A n alysis, pp. 279-285. Agronomy Monograph No. 9. Amer. Soc. o f
Agron.
34
P h i l i p , J . R. 1957. The th eory o f i n f i l t r a t i o n :
5. The
influen ce o f th e i n i t i a l m oistu re c o n te n t. Soil S ci. 84:329-339.
35 Poe, G ., and A. T. Edgerton. 1972. Soil m o isture mapping by
ground and a irb o rn e microwave radiom etry. In; National Oceanic and
Atmospheric A d m in istratio n Programs and U. S. Naval Research Laboratory
Programs, Vol. IV, pp. 93-1 to 93-23. Fourth Annual Earth Resources
Program Review, Manned S p a c e c ra ft C enter, Houston, Texas.
36 P r i e s t l y , C. H. B., and R. J . Taylor. 1972. On th e assessm ent
o f su rface h eat flu x and evap oratio n using l a r g e - s c a l e param eters.
Mon. Weather Rev. 100(2):81-92.
37 Reginato, R. J . , and C. H. M. van B avel. 1964. Soil w ater
measurement w ith gamna a t t e n u a t i o n . Soil S c i. Soc. Amer. Proc. 28(6):
721-724.
38 Reginato, R. J . , and R. D. Jackson. 1971. F ield measurement of
s o i 1-w ater c o n te n t by gamma-ray tra n sm issio n compensated f o r tem perature
f l u c t u a t i o n s . Soil S c i. Soc. Amer. Proc. 35(4):529-533.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission.
162
39 Reid, C. S. 1977. The u t i l i t y o f microwave remote sensing
techniques f o r s o il m oisture p r o f i l e d eterm in a tio n . Final Report,
NASA C o ntract, NAS 9-14251. Department o f E l e c tr i c a l Engineering,
U niversity o f Arkansas, F a y e t t e v i l l e , Arkansas. 139pp.
40 Richardson, C. W., and J . T. R itc h ie . 1973. Soil w ater balance
f o r small w atersheds. TRANSACTIONS o f the ASAE 1 6 (1 ):72-77.
41 R itc h ie , J . T. 1972. Model f o r p r e d ic tin g ev ap oration from a
row crop with incomplete co v er. Water Resour. Res. 8(5)-.1204-1213.
42 R itc h ie , J . T . , E. D. Rhoades, and C. W. Richardson.
C alcu latin g evaporation from n a tiv e grassland w atersheds.
of th e ASAE 1 9 (6 ):1098-1103.
1976.
TRANSACTIONS
43 Saxton, K. E ., H. P. Johnson, and R. H. Shaw. 1974. Modeling
e v a p o tra n s p ira tio n and s o il m o istu re. TRANSACTIONS of th e ASAE 17(4):
673-677.
44 Schmugge, T. J . , E. G. Njoku, E. Peck, and F. T. Ulaby. 1978.
Microwave and gamma r a d i a t i o n o b serv atio n s o f s o il m o istu re. In;.
Soil Moisture Workshop, pp. 5-1 to 5-37. NASA Conference P u b lic a tio n
2073.
45 Schmugge, T . , P. G loersen, T. W ilh e it, and F. Geiger. 1974.
Remote sensing o f s o il m o istu re with microwave rad io m ete rs. J . Geoohy.
Res. 79(2):317-323.
46 Schmugge, T ., T. W ilh e it, W. Webster, J r . , and P. G loersen. 1976.
Remote sensing o f s o il m o istu re with microwave rad io m ete rs— I I . NASA
Technical Note D-8321, Goddard Space F lig h t Center, G reen b elt, Maryland,
34pp.
47 S e l i r i o , I. S ., and D. M. Brown.
techniques f o r fallo w s o il in s p r in g .
1971. Moisture budgeting
Can. J. Soil S ci. 51:516-518.
48 Sewell, J. I . , and W. H. A llen . 1973. V is ib le and in f r a r e d remote
sensing in s o il m oisture d e te rm in a tio n . In; F. Shahrori ( e d . ) Remote
Sensing o f Earth Resources, Vol. I I , pp. 689-702. Tennessee Space
I n s t i t u t e , The U n iv ersity o f Tennessee, Tullahoma, Tennessee.
49 Thornthwaite, C. W. 1948. An approach toward a r a t i o n a l c l a s s i f i ­
c a tio n o f clim ate. The Geographical Review 38:55-94.
50 T roxler E le c tro n ic L a b o r a to rie s , Inc. 1972. I n s t r u c t i o n manual
f o r model 2376 two-probe d e n s it y gauge. Research T rian gle P ark, North
C aro lin a. 22pp.
51 Van Bavel, C. H. M. 1959.
m ission. Soil S ci. 87:50-58.
Soil densitom etry by gamma t r a n s ­
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
163
52 Van Bavel, C. H. M. 1966. P o te n tia l ev a p o ra tio n : The combina­
tio n concept and i t s experimental v e r i f i c a t i o n . Water Resour. Res.
2(3):455-467.
53 Van Bavel, C. H. M., and D. I . H i l l e l . 1975. A sim ulation study
o f s o il heat and m oisture dynamics as a ff e c te d by a dry mulch. Proc.
1975 Summer Computer Simulation Conf. , pp. 815-821. San F rancisco,
C a lif o r n ia . Sim ulation Councils, I n c . , La J o l l a , C a lif o r n ia .
54 Van Bavel, C. H. M., and D. I. H i l l e l . 1976. C alculating
p o te n tia l and actu al ev ap oration from a bare s o il s u rfa c e by sim ulation
o f co n cu rrent flow o f w ater and h eat. Agric. M eteorol. 17:453-476.
55 Van Bavel, C. H. M., and R. Lascano. 1979. Conservb, a numerical
method to compute s o il w ater c o n ten t and tem perature p r o f i l e s under a
bare s u rf a c e . NASA C o n tra c t, NAS 9-13904. Texas A&M U n iv ersity ,
College S ta t io n , Texas. 75pp.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
164
VITA
Name:
W alter Charles Bausch
Date and Place o f B ir th :
P aren ts:
Wife:
August 2, 1946, in San Antonio, Texas
Hugo and Mildred Bausch
Linda
C hildren:
Permanent Mailing Address:
Education:
Todd and C a rrie
Rt. 3, Box 15, Bandera, Texas
78003
High School Diploma, 1964, Bandera High School
B .S ., A g ric u ltu r a l E ngineering, 1969, Texas A&M U n iv e rs ity
M .S., A g r ic u ltu r a l E ngineering, 1971, Texas ASM U n iv e rs ity
S c h o la rsh ip s:
Doane Foundation S cho larship
Bandera County A&M Club S ch o la rsh ip
Texas A&M O pportunity Award S ch olarship
F e llo w s h ip s :' W. G. M ills Memorial Fellowship
Honors:
ASAE Honor Award
Alpha Zeta
Alpha Epsilon
Experience:
1975 to p r e s e n t, Research A s s o c ia te , Remote Sensing
C en ter, Texas A&M U n iv e r s ity , College S t a t i o n , Texas
1971 to 1975, Research A s s o c ia te , Texas A&M U niversity
Vegetable Research S t a t i o n , Texas A g ric u ltu ra l
Experiment S t a t i o n , Munday, Texas
1968 (summer), Engineer T ra in e e , Soil Conservation
S e r v ic e , Kennedy, Texas
1967 (summer), Engineer T ra in e e , Soil Conservation
S e r v ic e , San Antonio, Texas
This d i s s e r t a t i o n was typed by Mrs. Linda S tew art.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
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