An effective surface loss model for shallow water propagation and reverberation at mid-frequency that accounts for surface forward scattering

Abstract

A transport theory approach has been developed for modeling shallow water propagation and reverberation at mid-frequencies with emphasis at 1-3 kHz. With this approach, sea surface forward scattering can be taken into account in a 2-D (range-depth) approximation. The effects of surface forward scattering on reverberation level for typical conditions can be significant (>10 dB), even though bottom backscatter typically dominates reverberation in shallow water. However, effects of surface forward scattering have not been treatable with traditional ray-based codes, since it is implicit in these codes that the surface interaction is a specular reflection combined with some loss, and accounting for the change in grazing angle due to forward scattering, crucial for reverberation modeling, does not naturally come into it. A method to account for forward scattering with ray-based codes will be described. Transport theory results are used to develop an effective surface loss model. It is referred to as TOTLOS, for the surface loss for the total field, reflected plus scattered. While it is referred to as an effective surface loss model, the model can yield either loss or gain, depending on the grazing angle and other parameters of the environment. [Work supported by PMW-120 and ONR Code 322.]