Signal coherence in shallow water with rough boundaries

Abstract

A normal mode model to predict signal coherence for a source moving in shallow water with rough boundaries has been described previously [J. M. Ozard, G. H. Brooke, M. J. Wilmut, and M. V. Greening, J. Acoust. Soc. Am. Suppl. I 69, S19 (1981)]. The model assumes that mode amplitude or mode phase fluctuate. We have extended this model to widely spaced sensors by permitting the fluctuations to be independent from sensor to sensor. This new model has been used to calculate signal coherence for a variety of sensor configurations. Coherences have been calculated for low frequencies for which only a few modes are present. When source receiver range is changing rapidly it is found that for closely spaced sensors coherence depends only on receiver separation, mode shape, and mode excitation. However, for widely spaced sensors or sources that maintain a constant source receiver range the roughness parameters have a profound effect on coherence. Sensor configurations that give consistently high signal coherence, and those suitable for measuring signal coherence as a means to evaluating model parameters, are discussed.