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High resolution-cross sensor beam forming for a line array
Homer P. Bucker
Citation: The Journal of the Acoustical Society of America 62, S50 (1977);
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Published by the Acoustical Society of America
of America
SessionW. Underwater AcousticsIV: SignalProcessing(Precis-PosterSession)
Allen Elinthrope,Chairman
Naval UnderwaterSystemsCenter,New London, Connecticut06320
Precis-Poster Papers
Wl. High resolution-cross sensor beam forming for a line array. Homer P. Bucker (Code5311, Naval Ocean Systems Center, San Diego, CA 92152)
The methods of high resolution spectral analysis can be used
for high resolution cross-sensor beam forming. In this paper
two high resolution techniques (maximum entropy and exact
decomposition) are applied to the cross-sensor field. Sample
the case of a realistic
the effectiveness
of these
multiwave acoustic field plus narrow-
tributions in order to maintain its distribution-free performance. An efficiency measure for the sequential partition detector is calculated and it's shown to be bounded by Fisher's
The equations for the average sample number
and operating characteristic function are given in terms of the
number of quantiles estimated. For practical implementation,
it is shown that only a small number of quantiles need be estimated to give high efficiency. For example, estimating only
two quantlies gives an efficiency of 0.65 in Gaussian noise. Efficiencies as a function of m are given for Gaussian as well as
non-Gaussian noise distributions.
[Work supported by CNM.]
W2. Economical computation of array gain of large lattice
acoustic arrays
in anisotropic
sea noise.
Dr. Gordon E. Mar-
tin (Code 714, Naval Ocean Systems Center, San Diego, CA
The performance of an underwater acoustic array is dependent upon its gain in the presence of noise. While isotropic
noise is often utilized for simplistic considerations of system
performance, such analyses are of limited validity because
ambient sea noise is significantly directional. Thus, it is
necessary to evaluate the behavior of arrays having many elements and multi-dimensional configurations in realistic anisotropic sea noise. Such computations have been very expensive
using very large computers a•d impossible or impractical with
other computers. This paper describes a technique comparable to a multi-dimensional FFT for radically reduced cost
for the computation of array gain of lattice-shaped arrays of
one, two, or three dimensions. The computational aspects are
discussed. Typical results are presented for various horizontal and vertical arrays and compared with the author's prior
work reported at EASCON '75 and the Ninth International Congress on Acoustics, 1977.
Maximum entropy array processing.
D.P. Skinner (Code
791, Naval Coastal Systems Laboratory, Panama City, FL
32407) and D.G. Childers (Department Electrical Engineering,
FL 32611)
The maximum entropy spectral analysis technique is applied
to the problem of bearing estimation using a high-resolution
linear array. It is demonstrated via computer simulations
that the spatial response to an individual point scatterer increases in width in the presence of nearby targets as well as
with decreasing signal-to-noise ratio. It is also shown that
while the spatial response to a single point target is typically
much narrower for maximum entropy processing, the minimum angular separation required for the resolution of adjacent
targets is only slightly less (roughly a factor of one-half) than
that of a conventional beamformer even at high signal-to-noise
ratios (26 dB). These experimental r.esults are compared with
of the conventional
array and the maximum entropy array for both beamwidth and
resolution. The trends observed in the computer simulations
are in general agreement with the approximate theoretical results.
W3. Robust sequential detection using acoustical arrays in undefined noise. R.F. Dwyer (Naval Underwater Systems Center,
New London Laboratory, New London, CT 06320)
A technique is introduced which allows the design of a robust
sequential detector in undefined noise based on quantlies. For
each sampled output of M hydrophones, a set of m quantlies
from the unknown noise field are estimated and used to partition the observation space into known probability regions which
assure distribution-free performance. In addition, the effects
of hydrophone noise variations and non-uniform spatial noise
distributions are removed from degrading performance. It is
assumed that the noise samples are both spatially and temporally independent and the sig-nal is a plane wave arriving from
a specific direction. Once the m quantiles are estimated a
partitioned log likelihood ratio (PLLR) statistic is formed assuming a shift of scale alternative. The quantiles are esti•
mated in real time using a stochastic approximation algorithm
which allows the PLLR to adapt to slowly changing noise disJ. Acoust. Soc. Am., Vol. 62, Suppl. No. 1, Fall 1977
W5. Digital interpolation beamforming; concept and theory.
Roger G. Pridham (Raytheon Company, Submarine Signal Division, Portsmouth,
RI 02871).
For many applications, digital beamformers require an input rate which is significantly higher than that required for
waveform reconstruction
to achieve an adequate set of syn-
chronous beams. Typically, this high rate is realized in the
A/D conversion of the sensor outputs. A novel alternative,
discussed in this paper, is to sample the sensors at a rate
consistent with the Nyquist criterion and implement vernier
beamformer delays by digital interpolation. This technique,
which is referred to as digital interpolation beamforming, per-
mits an efficient partitioning between A/D converter and cable
bandwidth requirements and digital processing complexity.
The basic structure of an interpolation beamformer is presented. It is shown that interpolation filtering and beamforming can be interchanged to minimize digital processing. Beampattern degradation due to interpolation error is derived and
interpreted for the special case of a line array.
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