A Low- and Mid-Frequency Bistatic Scattering Model for the Ocean Surface

Abstract

Accurate bistatic active sonar performance predictions require accurate predictions of reverberation which in turn rely on accurate estimates of surface scattering strength. This paper describes a new semi-empirical model that estimates the surface scattering strength due to both the rough air-sea interface and subsurface bubble clouds, given the acoustic frequency (up to 10 kHz), incident and scattered grazing angles, bistatic angle, wind speed, and sound speed in the water. For the interface, small slope theory is used that accounts for surface-wave roughness spectra with low wavenumber cutoffs. For the bubbles, a stochastic volume scattering theory is used for frequencies up to 5 kHz and a transition function to handle 5-10 kHz. For both components, model parameters are determined from fits to significant sets of low- and mid-frequency open-ocean data. The broadband model is then used to highlight the relative influence of the two scattering mechanisms as a function of frequency, wind speed, and scattering angle