A FULL THREE-DIMENSIONAL, TWO-WAY, IMPLICIT FINITE DIFFERENCE PARABOLIC EQUATION MODEL FOR ACOUSTIC BACKSCATTERING IN THE OCEAN

摘要

A full three-dimensional (3D), two-way sound propagation model, FD3D2W, is developed to handle backscattered acoustic energy in 3D ocean environments. The model is based on a range-marching (KM) algorithm and a two-way coupling (TWC) approach. The RM algorithm is derived from a parabolic equation (PE) using the implicit finite difference (IFD) melhod. The TWC approach is based on the use of two continuity conditions at vertical boundaries. A 3D environment is discretized forming a sequence of stepwise range-independent regions that comprise azimuthal dependence. Within each region, the RM algorithm marches a pressure field forwards and backwards in range. At the vertical boundary between regions, the TWC approach solves for the reflected and transmitted fields from a sparse matrix equation using a row-index technique. Numerical studies are performed to demonstrate the superior performance of the FD3D2W model, and to preliminarily investigate 3D backscattering problems. Results show that the azimuth coupling is fully comprised in the FD3D2W model. Qualitative analyses also show that the FD3D2W solutions are consistent with analytical predictions. Furthermore, the computational speed of the model is encouragingly fast. In the studies, the running time for a two-way propagation is less than half an hour on a 200-MHz PC. It is concluded that the FD3D2W model forms a considerable alternative to existing 2D models for solving 3D backscattering problems.