Scattering of sound from laboratory breaking waves

Computer‐controlled gravity waves were generated to break in an anechoic tank. A sequence of 15 incident bursts was directed at the bubble cloud entrained by each breaking wave. A burst has seven cycles of a sine wave of frequency ranging from 10 to 15 kHz. The interval between adjacent bursts is set at 0.1 s in order to avoid overlapping the bursts. By analyzing the data of the 15 sound scattering events, the fluctuation was significantly reduced. The bubble clouds were observed to be roughly semicylindrical. The bubble size distribution in an entrained cloud was obtained from video images of a bubble cloud. This experimental information of the shape, size, and bubble size distribution of a bubble cloud was employed as the input into the theory adapted from Sarkar and Prosperetti [J. Acoust. Soc. Am. 93, 3128–3138 (1993)] to estimate the theoretical scattering strength. A comparison between the experimentally measured and the theoretically estimated scattering strengths will be shown. [Work supported by ONR.]