Sea surface effect on shallow-water reverberation

Wideband reverberation measurements were made at a fixed location in the East China Sea on 3 and 5 June 2001 using the same measurement system. Sound-speed profiles were similar during both measurements. Wind speed (W) and rms surface-wave height (sigma) changed from 2.74 m/s and 0.10 m on 3 June to 7.45 m/s and 0.33 m on 5 June. Thus, these measurements offer an opportunity to evaluate sea-surface effects on reverberation vertical coherence (RVC), RVC-inverted bottom acoustic parameters, and reverberation level (RL) in shallow water. The two sets of RVC and RL data, in a frequency range of 100-2500 Hz, show differences that are the apparent effects of the surface roughness. With increasing sea state, the RVC increases and the RL decreases. The effective bottom losses, inverted from the RVC data, correspond to the variation of sea state. This additional loss gives a physical explanation of the characteristics of both the measured RVC and RL. These preliminary findings show the importance of surface effects in shallow-water reverberation and propagation models. These effects would be pronounced for high frequencies and sea states. For the conditions reported here, the effects were most apparent for f > 500 Hz when W=7.45 m/s. (c) 2007 Acoustical Society of America.