Abstract:

The ensemble-averaged coherent and incoherent intensities are formulated for acoustic scattering by a smooth, bounded, elastic obstacle under the interface between two immiscible fluids with small-scale random roughness imposed. The formulation consists of combining Rayleigh-Rice perturbation theory for modeling propagation through the rough surface with a transition matrix solution for scattering by the obstacle near a planar surface. Results are applied to a spherical steel shell buried in a rough sediment bottom modeled with fluid parameters. It is demonstrated that the average incoherent field backscattered by the shell illuminated with shallow-grazing-angle acoustic sources can be well enhanced over field predictions based on scattering models where environmental surfaces are planar. Interestingly, the coherent intensity is also enhanced over flat interface predictions although not to the degree of the incoherent intensity. Implications to the acoustic detection and classification of buried obstacles are discussed. [Work supported by ONR.]