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

## 2pUW10. Intensity moments of underwater sound reflected by a Gaussian
spectrum corrugated surface: Measurements and comparison with a catastrophe
theory approximation.

**John S. Stroud
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*Univ. of Cincinnati, Dept. of Radiology, Cincinnati, OH 45267-0579
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**Philip L. Marston
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*Washington State Univ., Pullman, WA 99164-2814
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**Kevin L. Williams
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*Univ. of Washington, Seattle, WA 98105
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A surface, manufactured out of Styrofoam, provided a pressure release
surface for an underwater, forward-scattering investigation. This surface was a
single realization from a population of Gaussian spectrum random rough
corrugated surfaces (rms roughness 1.5 cm, correlation length 10 cm). A
broadband omnidirectional source was operated in the frequency range of 95--400
kHz and a broadband receiver was used to measure sound scattered from the
surface. The frequency dependence of the mth higher-order intensity moments
I[inf m] was measured and compared to theoretical predictions [M. V. Berry, J.
Phys. A 10, 2061--2081 (1977)] that I[inf m] is proportional to k[sup (nu)[inf
m]] (for m>2), where k is the wave number and (nu)[inf m] is a twinkling
exponent, and that I[inf 2](proportional to)ln k. Also, the dependence of I[inf
2] on distance from the surface was examined at a single frequency utilizing
various pulse durations. It is known that far from a surface the wave field will
obey Gaussian statistics (I[inf 2]=2). For short pulses, however, the statistics
of the wave field are strongly dependent upon individual reflections. For longer
pulses this is the case as well near the surface, but as one moves away it is
shown that the Gaussian limit is approached. [Work supported by ONR.]