Boundary element simulation of long‐range facet reverberation

Abstract

Simulation of seismoacoustic facet reverberation in an ocean waveguide requires solution of the full two‐way wave equation. Such simulations have been performed by means of finite difference and finite element methods. However, the computational requirements of these discrete methods have prohibited simulation for ranges larger than a few water depths. Here a hybrid boundary element‐wavenumber integration approach is presented to simulate long‐range facet reverberation. For a facet inhomogeneity in an otherwise horizontally stratified environment, the total field is expressed in terms of Green's theorem. By choosing a Green's function satisfying the boundary conditions at all horizontal interfaces, only the interface between the irregularity and the layered medium contributes to the surface integral in Green's theorem. Thus, only the boundary of the inhomogeneity needs to be discretized, with a spatial sampling independent of range. Here a modified version of SAFARI [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)] is applied to compute all Green's functions involved in the boundary integral, allowing analytical integration of the influence functions over each boundary element. After solving the boundary element equations, the total reverberant field is again computed by means of SAFARI. The approach is both efficient and general, allowing the exterior as well as the interior region to be a stratified elastic medium. Simulations will be presented for reverberation from a salt dome buried in the seabed as well as from Arctic ice facets. [Work supported in part by ONR Arctic Program Office.]