ASA 124th Meeting New Orleans 1992 October

3pUW1. Sound scattering from near-surface bubble clouds.

Jeff Schindall

Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677

William M. Carey

Defense Appl. Res. Project Agency, Arlington, VA 22202

Ronald A. Roy

Univ. of Washington, Seattle, WA 98103

Lawrence A. Crum

Michael Nicholas

Univ. of Mississippi, University, MS 38677

Recently an experiment was conducted to measure sound scattering from submerged bubble clouds generated in a fresh water lake at a depth of 87.5 m [Roy et al., J. Acoust. Soc. Am. 91, 2314(A) (1992)]. These clouds, which consisted of bubbles with a mean radius of 1.1 mm, were roughly cylindrical in shape with a nominal radius and length of 0.5 and 1.5 m, respectively. The backscatter target strengths measured below 1 kHz were large---of order 0 dB. Although the bubble size distributions were larger than those observed in the open ocean, these measurements, nevertheless, demonstrate the collective behavior characteristic of small bubbles occupying an acoustically compact space. This paper briefly reviews these experimental results and compares the acoustic characteristics of our clouds with those generated by breaking waves at sea. First, the dispersion curves and damping characteristics for these clouds are presented. Second, calculations for spherical and cylindrical clouds showing the scattering characteristics from the low to high frequencies are presented. Finally, the effect of the rough sea surface is estimated. [Work supported by ONR, ONT, AEAS, and NUSC/IR.]