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Comparison of double and triple cross correlation for arrival time identification of
amplitude- and frequency-modulated acoustic transient signals
Juliette W. Ioup, George E. Ioup, Robert L. Field, and James H. Leclere
Citation: The Journal of the Acoustical Society of America 84, S17 (1988);
View online: https://doi.org/10.1121/1.2025998
View Table of Contents: http://asa.scitation.org/toc/jas/84/S1
Published by the Acoustical Society of America
Anderson and Munson [J. Acoust. Soc.Am. 35, 1162-1168 (1963) ]
showedthat the directivityindex (DI) of an infinitelydenselypopulated
sphericalshellarraywasaboutequalto thatof a sphere.Extrapolatingto
discreteelements,this meansthe shellrequiresfar fewerelements.They
did not computeDI usingamplitudeshading,dueto the impracticalcost
of suchsystems
at that time.Today'stechnology
removesthat constraint.
Thisworkrevisitstheproblemwith shading,usinganapproachfor choosing the amplitudeshadingcoefficents
that maximizesDI [H.S.C. Wang,
J. Acoust. Soc.Am. 57, 1076-1084 (1975) ]. Calculationshavebeenmade
for the DI of shadedcubicvolumetricarrays,formingbeamsperpendicular to oneof its faces,in the presenceof isotropicnoise.Resultsshowthat
for 27 and 125elementarrayswith elementmatrixspacings
of 1/2 wavelength,a full 10 log (numberof elements)canbeobtainedfor DI. Work is
underwayto investigate
largerarraysandsmallerspacings.
The approach
will alsobe extendedto nonisotropicnoisefields. [Work supportedby
NORDA and NOSC exploratorydevelopment
programs.]
ocean.Coherentcombination
of the 120-channel
outputsrequiresknowledgeof individualelementamplitudeand phaseresponse
for accurate
results.Two in situmethodsof arraycalibrationaredescribed
andresults
from the September
experimentare presented.
The first methodused
transmissions
froma low-frequency
sourceof knownlocationandpower
level.Simulatingthe conditionsencountered
duringthe transmission,
the
powerarrivingat thearraywaspredicted
by severalacoustic
propagation
models.By comparingthe array response
at specificfrequencies
to the
responsepredictedby the models,an absolutecalibrationwas obtained.
An errorcurvefor thephasedatawasgenerated
byunwrapping
thephase,
accounting
for a samplingoffsetin thearray,andsubtracting
a multiple
linearregression
curve.Thesecond
methoddetermines
relativeamplitude
levelsby examiningtheaverageambientnoisepoweroutputof a specified
frequencybandacrossthearray.Usingspectral,coherence,
anddirectionality plots,thelevelof self-noise
in thearraywasshownto bebelowthat of
theambientnoisebeingmeasured.
Thesetwo independent
methodsprovide a consistentset of elementcalibrationvaluesusedfor array beamforming.[Work supportedby ONT. ]
9:00
H7. Least-squares and single-filter always-convergent iterative
deconvolutionof transient signals for correlation processing.James
H. Leclere,GeorgeE. !oup,a•JulietteW. Ioup,a•andRobertL. Field
9:15
H10. Abstract
withdrawn.
(Code 244, NORDA, StennisSpaceCenter,MS 39529)
Correlation processingfor distributedsensorsis most accuratefor
shortpulsesandthosewhoseautocorrelation
issharplyspiked.For longer
transientsignals,multipatharrivalsat eachsensorhavesignificantinterferencewith each other, and it is difficult to identify individual arrival
times.Deconvolutionof the receivedsignalto sharpenthe transientsis
onemethodto decreasethe overlapandincreasethe accuracywith which
travel timescan be identified.Deconvolutioncan also be appliedafter
crosscorrelationto sharpenthe autocorrelationof the transients.Leastsquaresdeconvolutionis the mostcommonlyusedapproachfor acoustic
signals.It hasthe disadvantage
of beingcomputerintensivewhenfilters
for long transientsare needed.An alternativeapproach,the single-filter
applicationof the always-convergent
iterativetechnique,isfasterandprovidesvariablecontrol for noise.The two techniquesare comparedfor
actualunderwateracousticmultipathtransientsignals.Singlefilter applicationof always-convergent
iterativenoiseremovaliscomparedto the use
of a modified Blackman-Harris
window for noise control. a) Also at the
Departmentof Physics,Universityof New Orleans.
9:05
H8. Comparisonof doubleand triple crosscorrelation for arrival time
identificationof amplitude-and frequency-modulated
acoustictransient
signals.JuliettcW. Ioup,'1 GeorgeE. Ioup,'• RobertL. Field, and
9:20
James H. Leclcre (Code 244, NORDA, StennisSpace Center, MS
39529)
The triplecrosscorrelationof threesignalsis a simultaneous
function
of two lags.It is an alternativeto crosscorrelationstakentwo at a time for
determiningthe lagsfor a givensourceat threedistributedsensors.It
shouldoffer improvementin arrival time identificationonly when the
statisticsof the signalhavesignificantthird momentcomponents.
In this
study,amplitude-and frequency-modulated
snythetictransientsignals
arepropagatedoverseveralpossible
pathsto threesensors,
andthe triple
correlationof the receivedpulsescomputed,aswell asthe crosscorrelations of the samethree signalstwo at a time. The efficacyof thesetwo
approaches
iscomparedfor a varietyof amplitude-andfrequency-modulatedtransientsignalsand multipathinterference
conditions.
a)Also at
the Departmentof Physics,Universityof New Orleans.
Hll. Matched-modeprocessing
correctionsfor array tilt and bottom
type, JamesA. Mercer (Applied PhysicsLaboratory, University of
Washington,Seattle,WA 98105)
In a relatedeffort,Homer Buckerhasshownthat matched-mode
processingfor an unknownsound-speed
environmentcan be significantly
improvedif correctionfactorsfor the mode-lineamplitudefunctionscan
be determined.
The correction
factors are obtained when a source with
knownlocationisavailable
to calibrate
thesystem.
Thispaperdescribes
the resultsof applyingthe sametechniquesfor simulatedcasesof unknownarray tilt andbottomcharacteristics.
9:25
H12. Self-consistentmodelingof signal and noisein a three-dimensional
9:10
environment.
JohnS. Perkins,W.A. Kuperman,andF. Ingenito(U.S.
Naval ResearchLaboratory,Code 5160, Washington,DC 20375-5000)
H9. In situ acoustic calibration for a large aperture array. Barbara
J. Sotirin (Marine PhysicalLaboratory A-005, ScrippsInstitution of
Oceanography,
La Jolla,CA 92093)
Previouspropagationwork is extendedto modelsurfacenoise,shipping, and signalsourcesin a fully three-dimensional
environment.The
During September1987,a largeapertureacousticarray wasdeployed
verticallyin the NortheastPacificto study low-frequencynoisein the
sumof a localcontributionandpropagationfromdistantsmallpatchesof
oceansurface.Propagationfrom any point to the array is madeefficient
S17
J. Acoust.Soc. Am. Suppl.1, Vol. 84, Fall 1988
noise
cross-spectral
density
matrixfora vertical
arrayiscomputed
asthe
2nd JointMeeting:AcousticalSocietiesof Americaand Japan
S17
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