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); View online: https://doi.org/10.1121/1.2016228 View Table of Contents: http://asa.scitation.org/toc/jas/62/S1 Published by the Acoustical Society of America S50 94thMeeting: Acoustical Society of America THURSDAY, 15 DECEMBER $50 ROYAL PALM ROOM, 9:00 A.M. 1977 SessionW. Underwater AcousticsIV: SignalProcessing(Precis-PosterSession) Allen Elinthrope,Chairman Naval UnderwaterSystemsCenter,New London, Connecticut06320 Precis-Poster Papers 9:00 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 calculations illustrate the case of a realistic band Gaussian the effectiveness of these methods in 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 Information. 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.] noise. 9:12 9:04 W4. 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 92152) 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, Gainesville, 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 theoretical derivations of the conventional linear beamformer 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. 9:16 9:08 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.