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

Univ. of Cincinnati, Dept. of Radiology, Cincinnati, OH 45267-0579

Philip L. Marston

Washington State Univ., Pullman, WA 99164-2814

Kevin L. Williams

Univ. of Washington, Seattle, WA 98105

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.]