### ASA 124th Meeting New Orleans 1992 October

## 5pPA1. Liquid-filled spherical reflectors: Analysis of glory ray
amplitudes.

**P. L. Marston
**

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N. H. Sun
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**
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*Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814
*

*
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Thin spherical shells filled with a liquid having a low speed of sound
c[sub i] are known to have enhanced high-frequency backscattering. It is
generally recognized that when the acoustic refractive index N=c/c[sub i] is
between [radical 2] and 2, the enhancement is associated with a two-chord
off-axis backscattered ray. A geometrical analysis of the amplitude diverges
since the Gaussian curvature of the outgoing wave front vanishes. In the
present research, a physical-optics analysis of glory ray scattering [P. L.
Marston and D. S. Langley, J. Acoust. Soc. Am. 73, 1464--1475 (1983)] was
applied to the ray of interest. Attention was limited to neutrally buoyant
spheres and shell effects were neglected in both the analysis and the
partial-wave series (PWS) calculations. The form function contribution is
proportional to (ka)[sup 1/2], where a is the sphere radius and k=(omega)/c.
For large ka, the analysis gives the major contribution to the PWS calculations
except for N near [radical 2] and 2. In this range for N the contribution has a
concise analytical approximation that depends on the ray impact parameter b =
a(N/2)[radical 4-N[sup 2]]. [Work supported by ONR.] [sup a)]Present address:
EXP Group, Inc., 44063 Fremont Blvd., Fremont, CA 94538.