Acoustic propagation through an internal wave field in a shallow water waveguide

Abstract

This paper addresses the problem of predicting and interpreting acoustic wave field properties in a stochastic ocean waveguide, for which the sound-speed variability within the water column is treated explicitly as a random process. It is assumed that the sound-speed distribution is composed of three components: a deterministic, time-independent profile and two stochastic components induced by internal wave activity. One random contribution represents a spatially diffuse Garrett–Munk field whose spectrum is constrained by the shallow water waveguide, while the second corresponds to spatially localized soliton packets. A high-angle elastic parabolic equation method is applied to compute single frequency realizations of the pressure field using this three-component representation of the sound-speed distribution. Ensemble-averaged transmission loss and scintillation index measures for the full pressure field and its modal components are estimated for different source depths and for both flat and sloping bottoms. Probability distributions of the mode amplitudes for different ranges are also presented. These statistical measures are incorporated into the analysis of range-dependent mode coupling between the internal wave and acoustic fields, and evidence is presented which supports a recent prediction that the scintillation index grows exponentially with range due to the competition between mode coupling and mode stripping found in shallow water waveguides. Full-field estimates of the scintillation index are also presented for a shallow water region on the continental slope off the New Jersey coast.