Synthetic aperture matched field approach to acoustic source localization in a shallow-water environment

Abstract

Matched field processing is a developing technique for localizing underwater acoustic sources and inverting measured acoustic fields for ocean waveguide properties. Considerable successes have been reported using this technique in deep water and, in the recent past, the technique has shown promise for localizing acoustic sources in shallow water. This paper describes an experiment conducted in the shallow water of the Western Bank near Sable Island on the eastern Canadian continental shelf. The experiment involved examining the localization performance of a small vertical array consisting of only four hydrophones and spanning approximately one-third of the water column against a relatively low signal-to-noise ratio source in a weakly range-dependent environment. In this experiment, the source emitted a series of low-frequency tones that were detectable by Fourier analysis of the received time-series. By estimating the phase of the received signal as a function of time, it was possible to estimate the relative change in the target range during an interval. Using a modified Bartlett matched field processor, the phase information was incorporated to estimate the true target range and depth during the same interval. The results of this experiment indicate that matched field localization can be dramatically improved by incorporating auxiliary information, such as the estimated signal phase history. In this case, the performance of the vertical receiving array approximates the expected performance of a planar array with the same vertical dimension as the actual receiver and a horizontal dimension controlled by the duration of the interval during which the phase history is estimated.