The low frequency radiation and scattering of sound from bubble clouds

The radiation and scattering from micro-bubble clouds with volume fractions greater than .01% are described using a theoretical model and measured data. In the low frequency limit, the radiation and scattering of sound was determined to be monopole when in the free field. The natural frequency of the cloud is predicted by a modified Minnaert equation. The measured backscatter target strength is consistent with theoretical expectations. These results show that both the production of sound by breaking waves and sea surface scattering is affected by these micro-bubble clouds and plumes either in whole or in part. Since these features are acoustically compact at the lower frequencies, a multipole expansion shows that the most important response is the monopole and its surface image.