5aUW7. Computations of rough surface reflection coefficients in a waveguide.

Session: Friday Morning, December 6

Time: 9:16

Author: David H. Berman
Location: Dept. of Phys. and Astron., Univ. of Iowa, Iowa City, IA 52242


The effect of rough interface scattering in a waveguide is complicated by the possibility of scattered sound returning to the rough interface and then rescattering. A formalism for determining the effect of such rescattering on the mean field was developed in a previous paper [D. H. Berman, J. Acoust. Soc. Am. 96, 417--426 (1994)], and similar formalisms are described in A. G. Voronovich [Wave Scattering from Rough Surfaces (Springer-Verlag, Berlin, 1994)]. It has been argued that the effect of re-scattering will be small if the skip distance of rays associated with normal modes is larger than the correlation length of surface roughness. Using numerical evaluations of the Bourret approximation for the mean field, it is shown here that for correlation lengths comparable to the skip distance, rescattering can contribute significantly to the effective reflection coefficient for the mean field. However, it will also be shown that a good approximation to the effective reflection coefficient can be obtained by replacing the true surface roughness by a multiple of the surface roughness. The multiple is determined by the ratio of skip distance to correlation length. [Work supported by ONR.]

ASA 132nd meeting - Hawaii, December 1996