John B. Schneider
Shira Lynn Broschat
Patrick J. Flynn
School of Elec. Eng. and Comput. Sci., Washington State Univ., Pullman, WA 99164-2752
The propagation of acoustic energy in a shallow water environment is studied using a two-dimensional, staggered-grid finite-difference model. Such a model allows one to view the propagation of energy in the time domain throughout the region of interest. Since fields are available ``everywhere,'' the model can be used to guide the development of robust schemes for the detection of scatterers in the water column or buried in the sediment. In addition, it can be used to benchmark approximate models for acoustic propagation and scattering in shallow water. This paper considers the effect of different physical features on the possible identification of scatterers. Such scattering mechanisms as top and bottom roughness and inhomogeneities in the water column are considered. Monte Carlo simulations are used to gauge the relative effects of these features. Frequencies on the order of 7.5 kHz are considered for depths up to 30 m. The implementation used here includes several enhancements over traditional finite-difference models. For example, typical finite difference models approximate continuously varying material interfaces by an interface that appears like a staircase---the material properties change only at discrete location. For this research a conformal technique is used to model more accurately the continuous interface. [Work supported by ONR.]