Analysis of free bubble-cloud scattering data from the Lake Seneca experiment

In the Fall of 1991, a series of experiments were conducted at the Seneca Lake test facility which measured the frequency-dependent scattering from submerged bubble clouds (1,2). The results showed that certain features of the high-frequency backscatter data were consistent with single-bubble scattering while the low-frequency results were consistent with collective oscillations of the bubble cloud. A monopole resonance scattering peak was evident and scaled with the bubble cloud volume and the mixture sound speed. Analysis showed that the evolving target strength of the cloud as it rose through the beam exhibited an interference effect which could explain the differences between calculated and measured scattering strengths (3). Advanced signal processing and modeling techniques have been developed to enable the removal of experimental artifacts caused by, 1) uncertainties in the range geometry, 2) coherent electrical noise in the processing electronics and 3) acoustic reverberation within the test volume. The resulting backscattered target strength is comparable to that previously reported.