Modeling of three-dimensional seismoacoustic reverberation from anisotropic roughness patches

Abstract

A perturbation approach to narrow- and wideband modeling of scattering from roughness patches on an interface separating a fluid and an elastic half-space has previously been developed [LePage and Schmidt, J. Acoust. Soc. Am. 89, 1941(A) (1991)]. However, based on a 2-D Fourier transform formulation it allows for modeling of the scattered near-field only, and it prohibits incorporation of waveguide effects. Here, a coordinate transformation is presented, yielding a representation of the virtual seismic moment sources for the scattered field in cylindrical coordinates. This source representation is compatible with the 3-D version of the OASES/SAFARI code, which has consequently been modified to provide extremely efficient numerical simulation of seismoacoustic reverberation in shallow- and deep-water waveguides. This new model has been applied to model the reverberation from horizontal roughness patches in the ARSRP mid-Atlantic environment. The model’s efficiency has allowed for Monte Carlo estimation of the statistical properties of the reverberation from patches with anisotropic roughness statistics, including mean reverberation intensity and spatial correlation. The effects of roughness anisotropy, bottom elasticity and the waveguide physics are discussed. The principal result of this theoretical analysis is the conclusion that Lambert’s law is totally inadequate for representing bistatic bottom reverberation. This conclusion is consistent with the results of the analysis of the bistatic data from the ARSRP experiment, as discussed in the companion paper by Bondaryk etal. [Work supported by ONR.]