Abstract:
The physics of sound propagation in saturated, porous (Biot) media differs from propagation in fluids and elastic/anelastic solids because of the existence of a second compressional wave, the ``slow'' wave. Many environments in bottom-interacting ocean acoustics consist of mud and sands which can be modeled as saturated, porous solids with low shear moduli. In order to understand the physical mechanisms responsible for acoustic propagation, attenuation and scattering in porous media, and to determine if the ``slow'' wave plays a role in these processes, we have extended our numerical scattering chamber (NSC) code to solve Biot's equations in two-dimensional Cartesian coordinates. The NSC formulation is based on the method of time domain finite differences and is applicable to the rough and laterally heterogeneous structures that are found on the seafloor. Within the same NSC code we can compare acoustic, elastic, anelastic, and Biot models for realistic environments with sub-bottom heterogeneities and seafloor roughness with scale lengths comparable to acoustic wavelengths. All multiple interactions and mode conversions are included in the solutions. [Work supported by ONR.]