Extended towed array processing by an overlap correlator

Abstract

A method of extending towed array measurements that provides an aperture greater than that of the physical array is presented. Such a technique can be used by matched-field estimators to obtain information about the range and depth of a source and in other towed array applications requiring a very large aperture. The approach is to combine coherently the acoustic signals arriving at a moving array of hydrophones by making proper compensation through a factor that corrects for considerable fluctuations in phase irregularities in the tow path of the physical array as well as fluctuations in amplitude experienced during the coherent integration time. In this manner, the finite aperture of the physical array is exploited in a process that synthesizes the extended aperture of the method. The concept is based on an algorithm that we call an ‘‘overlap correlator,’’ which provides the phase correction factor by correlating overlapping space samples of the acoustic signal received at successive moments by the moving towed array. This is in contrast to the standard, passive synthetic aperture technique, which requires either highly accurate a priori knowledge of the source frequency or a maneuver in order to obtain a wavenumber or bearing estimate. The algorithm has been tested on numerical data generated by the SACLANT Undersea Research Centre’s normal mode model SNAP. The effects of space and time coherence of the signal and the random and systematic errors on the extended towed array measurements are examined and used to derive guidelines for experimental applications of this algorithm.

Research on Location of Line Spectrum of Underwater Target Based on Passive Synthetic Aperture Method

“…(a) Principle of passive synthetic aperture In passive synthetic aperture processing, the parameters of the target are estimated by virtue of the radiated signal of the underwater target received by the virtual array [5][6][7]. As shown in Fig.1, underwater target moves in a strait line, and the nearest distance between the measuring hydrophone and the underwater target's ideal track is R0, and the radiated noise signal is sampled by the measuring hydrophone.…”

“…From equation (7), ( ) a R t is the function of azimuth time a t which shows the variation of the doppler shift. Azimuth compression can be implemented according to equation (6) in time domain or frequency domain.…”

Ocean, platform, and signal processing effects on synthetic aperture sonar performance

“…The 'new approach' mentioned by Candy and Sullivan was published by Stergiopoulos and Sullivan [1989] one month later, and showed a method of extending towed array measurements. The concept was based on what the authors referred to as an "overlap correlator," which provides a phase correction by correlating successive and overlapping array samples of the acoustic signal received by a moving towed array.…”

Circular Radon Transform Inversion Technique in Synthetic Aperture Ultrasound Imaging: an Ultrasound Phantom Evaluation

“…Initially implemented in remote sensing/imaging by radars (Moreira, 1992;Perry, Martinson, 1978) and in sonar imaging (Stergiopoulos, Sullivan, 1989; Yen, Carey, 1989) later they found their application in the ultrasound imaging (Corl et al, 1978;Nagai, 1985;Ozaki et al, 1988), where they are also known as synthetic aperture focusing techniques (SAFT). In SAFT imaging, at each time a single array element acts as a point source emitting a spherical wave to the acoustic medium and as a receiver of the echo signal back-scattered from the inhomogeneities (O'Donnell, Thomas, 1992; Thomson, 1984).…”