Adaptive Methods in Underwater Acoustics

The NATO Advanced Study Institute on Adaptive Methods in Underwater Acoustics was held on 30 July - 10 August 1984 in LLineburg, Germany. The Institute was primarily concerned with signal processing for underwater appl ica­ tions. The majority of the presentations, when taken together, yield a definite picture of the present status of understanding of adaptive and high resolution processing, setting out the progress achieved over the past four years together with the major problem areas remaining. Major effort was made to obtain a commensurate contribution of tutorial and advanced research papers. It is my hope that the material in this volume may be equally well suited for students getting an introduction to some of the basic problems in underwater signal processing and for the professionals who may obtain an up-to-date overview of the present state of the art. This might be especially useful in view of the controversy and lack of adequate interrelationships which have marked this rapidly expanding field in the past. Practical reinforcement of this picture is provided by the material concerning digital and optical processing technology, giving some guidance to achievable adaptive and high resolution techniques with current processing devices. The formal programme was extended and detailed by a series of six evening work­ shops on specific topics, during which informal discussions took place among the participants. Summaries of these workshops are also included in these Proceedings.

1. Acoustical Background of Signal Processing.- Twenty years of signal processing.- Ambient noise: characteristics of the noise field.- An analytical method to predict the statistical characteristics of ambient shipping noise.- Statistical aspects of sound propagation in the ocean.- Towed array response to ship noise: a near-field propagation problem.- Three-dimensional FFP model of acoustic- and elastic wave propagation in horizontally layered media.- Seismic sensors in underwater acoustics: results from sea-floor measurements in areas of different geology.- Underwater acoustics in the Arctic Ocean.- A new theory for the transmission and reflection coefficient of layered systems.- Second moments of the pressure field near a smooth caustic.- Stochastic systems theory of the scattering of waves from a random medium.- Hydrodynamic flow noise in hydrophones.- Wavevector structure of turbulent wall pressure and its filtering by normal transmission and spatial averaging in sensor arrays.- Target strength and echo structure.- 2. Theoretical and Practical Aspects of Signal Processing.- Time delay estimation.- Time delay estimation in the presence of multipath propagation.- Constrained time delay estimation via zero-crossing methods.- Range and bearing determination: Maximum Likelihood and Kalman-Bucy techniques.- Delay estimation with nonstationary signals and correlated observation noises.- Source parameter estimation by approximate Maximum Likelihood.- On the use of focused horizontal arrays as mode separation and source location devices in ocean acoustics.- High-resolution source-depth estimation in ice covered shallow water.- Spectrum analysis: overview of classical and high resolution spectral estimation.- Application of high resolution spatial processing methods to real data of a fixed array in shallow water.- Experimentation of spatial processing methods.- Simultaneous estimation of spectral lines and of a superimposed continuous spectral density.- Fitting sinusoids to sampled data and correlation sequences.- An extended maximum entropy method for high resolution spatial processing.- Spectral and interspectral analysis of low frequency submarine acoustic signals received on an array of sensors.- Overview of adaptive array processing.- New approaches in the adaptive array processing field.- Multiple detection using eigenvalues when the noise spatial coherence is partially unknown.- Theoretical and experimental comparisons of optimum element, beam and eigen space array processors.- Applications of some statistical measures to spatial signal processing.- The cross correlation matrix in spatial processing.- The effect of bandwidth on the performance of a postbeamformer interference canceller.- A new approach to the design of broadband element space antenna array processors.- On the role of prior information in nonlinear bearing estimation.- Beamforming by the cross-correlation analysis of received spectra.- Applications of adaptive array processing.- Adaptive active sonar reception in shallow water using vertical array outputs covariance matrix eigenvalues: experimental results.- Beamforming with a distorted towed array.- Influence of hydrophone position errors on spatial signal processing algorithms.- A tutorial introduction to nonlinear filtering.- Detection with uncertainty: Nonparametric, robust or adaptive approaches.- The design of optimal processors for arrays with non-Gaussian noise inputs.- Adaptive processing of underwater acoustic signals in non-Gaussian noise environments: I. Detection in the space-time threshold regimes.- Detection and classification phenomena of biological systems.- Detection and recognition of moving or randomly scaled objects.- Iterative algorithms for deconvolution and reconstruction of multidimensional signals from their projections.- 3. Techniques and Applications.- Digital signal processing for sonar.- Optical signal processing.- Beamforming for sonar signals by means of an incoherent acousto-optical processor: experimental results.- Adaptation of fiber optics to hydrophone applications.- Ceramic elastomer composite hydrophone.- Expert systems for ship noise interpretation.- Comparison of the statistical and the expert system approach for the interpretation of ship noise.- Signal processing techniques to analyse and simulate radiated underwater ship propeller noise.- Signal processing in ocean tomography.- New advances towards ocean, acoustics and space integration.- Passive synthetic aperture sonar — an analysis of the beamforming process.- Techniques for measuring backscattering from the sea floor with an array.- AEON — adaptive time-space array processing.- Summaries of Workshops.