ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

5aUW10. Benchmarks for backscatter in parabolic evolution.

Eric Smith

Appl. Res. Labs., Univ. of Texas, Austin, TX 78713-8029

Recently, a method was described for improving parabolic equations to account for intermediate backscattering induced by slow range dependence of the acoustic index of refraction. The method has found difficulty gaining acceptance, though, because there have been no readily available benchmarks for the systems to which it applies. This paper presents a method for constructing a class of benchmarks, by means of which a parabolic equation can be used to test itself for correct evolution through variations in sound speed. The method makes use of the conformal equivalence of changes in acoustic index of refraction to changes in geometry. As examples within this class, a set of special cases is treated analytically. These are exactly solvable models, in which intermediate backscattering leads to recognizable and physically significant effects. In particular, they can be used to show why energy conservation alone is not a sufficient requirement to produce correct parabolic evolution, even when it is physically appropriate. [Work supported by the ARL:UT Independent Research and Development Initiative.]