Modeling vertical coherence of wave breaking noise in shallow water and comparison with field measurements

Ambient noise data have been collected in shallow waters of Bay of Bengal up to a frequency of 10 kHz under calm conditions and also with wind induced wave breaking events. It is noted that during the passage of the breaking wave noise spectrum is much increased in the band of 1 to 10 kHz. Complex vertical coherence between receivers with and without breaking events are examined. Zero crossing frequency of real coherence in the case of breaking waves are very much reduced when compared to calm conditions. Time averaged coherence for wind generated noise is a relatively stable feature which is independent of the temporal variations in the ocean environment, but largely controlled by the bottom boundary. Hence wind/wave generated noise is modeled as a uniform distribution of surface sources with near iso-velocity water column conditions and the effects of the sea bed on the noise coherence is examined using a homogeneous half space sea bed. The measured coherence for breaking waves is then compared with the modeled coherence and the results are presented.