A Numerical Scattering Chamber for Studying Reverberation in the Seafloor

Abstract

A numerical scattering chamber, based on the finite difference solution to the two-way elastic (or anelastic) wave equation in the time domain, is a powerful and convenient approach to studying the physics of surface and volume reverberation at the seafloor. Scattering from both surface roughness and volume heterogeneities at scale lengths comparable to wavelengths can be treated. The method includes all shear wave and interface wave effects and all multiple interactions between scatterers. Bottom parameters varying from soft sediments (with shear wave velocities much less than water velocity) to hard basalts (with shear velocities higher than water velocity) are studied. We use a Gaussian pulse-beam as the incident field and we compute the resultant scattered field (in compressional and shear wave energy density) on arrays of receivers surrounding the scattering region. Backscatter coefficients, defined as the ratio of the energy in the scattered beam at a given angle to the energy in the incident beam, can be computed. For example, for an incident beam at fifteen degrees grazing angle, the coefficient for direct backscattering from a very rough, basaltic seafloor is -17dB.