Dept. of Ocean Eng., MIT, Cambridge, MA 02139
Previously a hybrid boundary element and full wave solution technique was presented for two-dimensional acoustic propagation in laterally inhomogeneous, vertically stratified medium [W. Seong and H. Schmidt, J. Acoust. Soc. Am. Suppl. 1 86, S54 (1989)]. The technique involved dividing the range-dependent ocean into range-independent sectors with the field within each sector expressed as a boundary integral over the vertical sector boundaries in terms of a set of unknown boundary displacements. The approach gave both the forward propagating field and the backscattered component and was global since it involved the solution of a matrix relation, the coefficients of which were obtained from matching boundary conditions along vertical cuts distributed throughout the entire computational domain. However, for ocean environments with continuously changing bathymetry, the construction of this matrix in a global manner presents a severe computational load, especially in the amount of core memory required. This deficiency motivated the search for a more efficient formulation of the hybrid scheme. By employing the single-scatter approximation, where the back-scattered component from the forward vertical boundary is neglected, a computationally efficient forward marching scheme can be derived. The algorithm is illustrated using various test cases involving range-dependent bathymetric features.