A comparison of the finite-difference time-domain and integral equation methods for scattering from shallow water sediment bottoms

Abstract

Scattering from sediment bottoms has a significant effect on acoustic propagation in shallow water. When shear effects are negligible, the water–sediment interface can be modeled using a fluid–fluid model. In this paper, finite-difference time-domain (FDTD) and integral equation (IE) results are compared for a fluid–fluid rough interface. Both methods are exact in that they make no physical approximations, and both can be used either to benchmark approximate analytical methods or to study the propagation problem directly. The comparison presented verifies the numerical accuracy of the two methods. Scattering strengths are computed using a Monte Carlo average over a set of 50 surfaces. Results for single surface realizations are presented as well. Both single-scale Gaussian and multiscale modified power law (MPL) roughness spectra results are presented. While the MPL spectrum is more realistic for shallow water problems, the Gaussian spectrum gives low scattering levels in the backscatter direction, permitting a stringent test of numerical accuracy. Several different bottom types are considered for which the shear speeds are negligible, and attenuation has not been included. For all cases, the FDTD and IE results are obtained using the same surface realizations. In general, the results agree well. [Work supported by ONR.]