Theoretical model of acoustic backscatter from a smooth seabed

Currently available mathematical models of acoustic scattering from the ocean bottom generally fail to predict backscatter levels of sufficient magnitude for two limiting cases: as the bottom becomes increasingly smooth and as the grazing angle becomes small. In this paper a mathematical model of acoustic backscattering that attempts to address these shortcomings for the case of a sediment bottom is derived. In the model, scattering is caused by fluctuations in sediment porosity. The model allows for penetration of the incident wave into the bottom at subcritical grazing, and retransmission of scattered spherical waves through the (planar) interface. The frequency and grazing angle dependence of the acoustic backscatter are determined primarily by the correlation function of the porosity fluctuations, while the magnitude of the backscatter is controlled by the mean-square value of these fluctuations. Numerical results obtained from the model are tested against backscatter data available in the literature for several sediment bottoms over a wide range of frequencies (30–500 kHz). Agreement between the model and literature data is good.