Abstract:
The finite-difference time-domain (FDTD) method provides a robust and accurate means of studying a wide range of propagation and scattering problems. However, the FDTD method, though simple to implement and readily parallelizable, is computationally expensive. In this paper, a benchmark sea surface scattering problem [Thorsos, Reverberation and Scattering Workshop, Gulfport, MS (1994)] is used to show how the computational requirements of an FDTD solution can be mitigated. A contour-path approach is used so that the grid conforms to the continuously varying surface. This permits accurate modeling of the rough surface without requiring an excessive number of points per wavelength. Errors due to numerical dispersion are reduced by adjustment of the phase speed. Although the test-case problem has both transmitting and receiving arrays in the near field of the scattering surface, simple near-field to near-field transformations are used so that the transmitting and receiving arrays need not be included in the computational grid. These transformations significantly reduce the size of the grid and, correspondingly, the computational resources needed to obtain a solution. The problem considered here has been studied previously using time-harmonic techniques; however, an FDTD solution allows results to be obtained over a broad spectrum. The modifications needed to obtain broadband results are discussed. [Work supported by ONR.]