Kevin LePage
Henrik Schmidt
Dept. of Ocean Eng., MIT, Cambridge, MA 02139
Broadband synthetic seismograms of scattering from two dimensionally rough surfaces in a three dimensional, but horizontally stratified media are presented. These results are obtained using the elastic perturbation theory of Kuperman and Schmidt [J. Acoust. Soc. Am. 86, 1511--1522 (1989)] under the Born approximation, for scattering scenarios where rough surfaces of finite extent, which are different on each interface, are insonified by an acoustic point source. These results, while constrained to the single scattering physics of perturbation theory, graphically illustrate the conversion of acoustic energy into trapped Scholte interface modes on elastic half-spaces, and Von Schmidt, antisymmetric, horizontally polarized shear (SH) and Love waves in elastic layers, as well as into a continuous scattered spectrum in the water column. Examples include a small compact scatterer attached to an elastic plate insonified by an acoustic point source, where forward scattering into the flexural mode, backscattering into the quasilongitudinal mode and out-of-plane scattering into the SH mode may be observed. Point source scattering from a larger scattering region is also illustrated, where the effects of wave front curvature become important. The scattering region, which is a stochastic realization of an isotropic power law surface, excites forward-scattered flexural waves in a broad beam, but it is continuously observed that the off axis response is dominated by shear waves. Other scattering scenarios are also presented where the three-dimensional aspects of scattering continue to be important, even for plane wave incidence. [Work supported by ONR.]