Signal coherence model for widely spaced sensors in shallow water with rough boundaries
Keywords:underwater sound, shallow water, rough boundaries, normal modes, waveguide, signal coherence, source-receiver range
AbstractA model based on normal modes has been developed to predict signal coherence for a sound source in a shallow water waveguide with rough boundaries. Deterministic amplitudes and phases are calculated from a normal mode model and random phase or amplitude fluctuations are added. The model assumes that the mode phase fluctuates as a result of the water boundary roughness and that the fluctuations have a degree of independence that may be chosen arbitrarily. This independence is intended to account for the effect of large sensor separations. Receivers may be in any configuration but the source is restricted to the limiting cases of motions that either maintain the source-receiver range constant or change it by many wavelengths during the coherence estimation period. When the source-receiver range is changing rapidly and the receivers are closely spaced, it is found that the signal coherence depends only on receiver separation, mode shape and mode excitation. For closely spaced sensors broadside configurations give consistently high signal coherence. However, for widely spaced sensors and/or sources that maintain a constant source-receiver range the roughness parameters can have a profound effect on coherence. It is also found that certain configurations may be used to isolate the effect on coherence. It is also found that certain configurations may be used to isolate the effect of the various model parameters, and hence may be used to measure these parameters experimentally.
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