Environmentally sensitive adaptive fluctuation-based processing

Abstract

Signals that propagate from submerged sources to submerged receivers in the ocean generally interact less with the fluctuation generation mechanisms near the sea surface, e.g., internal and sea-surface waves, than signals originating near the surface, e.g., surface ship clutter and sea-surface noise. Therefore, submerged source signals generally have smaller fluc- tuations than clutter signals and noise. The differences in amplitudes of fluctuations have been used to devise a class of signal processing algorithms that provides preferential gains for signals having fluctuation amplitudes less than those of clutter and noise. Gains include increases in signal-to-noise ratio, clutter suppression, and unalerted automatic detection. The AWSUM filter is an example of such a processor [R. A. Wagstaff, IEEE J. Oceanic Eng. 22(1) (1997)]. Similar gains can be achieved by exploiting the order dependence of fluctuation amplitudes. By combining amplitude dependence and order dependence, an algorithm has been devised that is both sensitive to fluctuations and adapts to the input data. The resulting algorithm is designated the AWSUM Environmentally Sensitive Adaptation (ESA). The AWSUM ESA algorithm is described and results from processing real data are presented. [Work supported by ONR and NRL.]