Abstract:
The effect of horizontal inhomogeneities in sediment properties on acoustic scattering is modeled as a problem of diffraction by random apertures over a randomly stratified medium, by numerical simulation. Apertures of varying geometries were investigated. The ocean sediment is modeled in two steps. (1) The granularity is modeled as an ensemble average of a randomly layered poroelastic material, in which each layer represented a granular material of a particular grain size, and the thickness of each layer was related to the associated grain size and porosity by a conservation-of-mass relationship. (2) Lateral variations are approximated by performing a coherent ensemble average of results from several realizations of the randomly stratified medium in which the incident and scattered sound wave enter and exit the sediment interface through an aperture. Poroelastic medium parameters were chosen to represent water-saturated sand. The mean and standard deviations of the grain-size distribution were chosen to match existing experimental data. Scattered signals were computed for a selection of aperture functions and at various grazing angles. The angular variations in the scattering strength were compared. [Work supported by ONR Code 321 OA.]