ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pUW24. Marching wave-number-integration approach to range-dependent, two-way seismoacoustic propagation modeling.

Henrik Schmidt

Dept. of Ocean Eng., MIT, Cambridge, MA 02139

An approximate solution to two-way seismoacoustic propagation problems can be obtained by recursive use of wave-number-integration in a stepwise range-dependent environment. The approach is conceptually simple and straightforward. In the range-independent sector containing the source, an ``exact'' integral representation of the field can be obtained versus range and depth using, e.g., the SAFARI/OASES code [H. Schmidt and F. B. Jensen, 813--825 (1985)]. At the vertical boundary of the next sector we then solve the reflection-transmission problem locally for each plane-wave component, assuming vertical homogeneity of the field. The resulting particle motions now act as virtual sources, the wave-number representation of which can be stated explicitly using the seismic source representation theorem. The resulting transmitted and reflected fields can then be computed at any depth and range within the range-dependent sectors. The procedure is repeated at any vertical cut in a marching scheme. A single-scatter approximation to the backscattered field is subsequently obtained by a backward marching scheme, similarly to the approach used in the two-way elastic PE [M. D. Collins, 1815--1824 (1993)]. A special version of OASES incorporating this approach has been developed, and its performance is demonstrated by solutions to canonical problems such as the ASA benchmark, and seismic problems previously solved using the two-way elastic PE.