Reflection of acoustic waves at a water–sediment interface

TLDR

Reflection and refraction of plane acoustic waves are investigated when the sediment is modeled as a porous viscoelastic medium. The model employs Biot’s theory, which predicts three distinct attenuating body waves in the porous sediment. When water plane waves strike the interface, they generate three nonhomogeneous waves in the sediment whose elliptic particle motion, angle‑dependent velocity and attenuation, and lack of a critical angle lead to frequency‑dependent reflectivity that can differ markedly from a solid model and acts as a broadband filter.

Abstract

Reflection and refraction of plane acoustic waves are studied for the case where the sediment is modeled as a porous viscoelastic medium. The model is based on the classical work of Biot which predicts that three different kinds of attenuating body wave may propagate in the sediment. As a consequence when homogeneous plane waves in water are incident to a water–sediment interface, three nonhomogeneous waves are generated in the sediment. In these waves the direction of phase propagation and the direction of maximum attenuation are not the same and particle motion follows an elliptic path. Moreover the velocity and attenuation of the refracted waves become dependent on the angle of incidence and no ’’critical’’ angle occurs. Numerical examples show that in some cases the reflectivity of a porous viscoelastic model differs significantly from the case where the sediment is modeled as a viscoelastic solid with constant complex modulus. Finally because of the frequency dependence of reflectivity in the porous model, it is found to act as a filter with respect to broadband energy.