A composite model for rough bottom scattering

To be valid and accurate, any model for mid-frequency bistatic scattering must account for the different scales of roughness found on the bottom. A composite scattering model was first introduced by Kuryanov. An extension for this model, similar to the one by Kuryanov, was applied to data acquired during the 1993 ARSRP cruise. In this model, the scattering surface is represented by a random surface composed of facets. Each facet is parametrized by a mean slope to account for large scale roughness and a perturbation to account for small scale roughness. First, partial coherence of the field over the facet surface is used to determine the contribution of each individual facet. Then, the scattered field is calculated via incoherent addition of the contributions from all facets. The choice of a Gaussian distribution for the mean slope of the facets results in a good match between the large scale roughness spectrum and the empirical power law. A simplified model for scattering from the individual facets assumes that all scatter is directed into the specular direction. This allows a completely analytical solution and is in reasonable agreement with experimental data. [Work supported by ONR.]