MONOSTATIC AND BISTATIC RAY ACOUSTIC SCATTERING BY SUBMERGED ELASTIC SPHERICAL-SHELLS

This paper applies uniform ray asymptotics to plane-wave far-field sca ttering by submerged thin elastic spherical shells based on an earlier study [J. M. Ho and L. B. Felsen, J. Acoust. Sec. Am. 88, 2389-2414 ( 1990)]. It also performs numerical implementation to clarify the ray s ynthesis accuracy and to examine the constituent waves and fields. Spe cifically, in addition to the frequency response, the scattering patte rn is also evaluated which demonstrates the connection between bistati c (regular) and backscattering (axial focusing). It is found that the major contribution to the total scattered field is from specular refle ction, a supersonic compressional wave, and their interaction effect w hen adjacent, plus a creeping wave field in the forward scattering ran ge-much the same as with the cylindrical shell prototype [J. M. Ho, J. Acoust. Sec. Am. 94, 2936-2946 (1993)], save from the spherical focus ing of the shell-guided waves here. These wave objects together reprod uce the scattering signature, as generated by the exact normal-mode se ries solution, very accurately for ka greater than or equal to 5 or so .