ASA 124th Meeting New Orleans 1992 October

5pUW9. Effects of surface-wave forward scattering on near-surface acoustics fields.

Frank S. Henyey

John Ballard

Terry E. Ewart

Eric I. Thorsos

Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105

David M. Farmer

Steven Hill

Inst. for Ocean Sci., Sidney, BC, Canada

The backscattering return from bubble clouds is proportional to the fourth power of the ensonifying field. This field, as determined by the interference of the direct field and that reflected from the wavy surface, has been studied both by modeling and by experiment. The modeling uses accurate wave methods, but is restricted to one horizontal dimension. The forward surface scattering experiment (FOSS) was carried out during the 1992 Gulf of Alaska reverberation experimental program. Both cw transmissions and explosive charges (1 oz. of high explosive) were used as sources in order to determine the temporal and frequency dependencies, respectively. The modeling and experimental results are compared, involving the strength, the frequency dependence, and the frequency shift (``Doppler'') spectrum. [Work supported by ONR.]