Modal characteristics of acoustic signal fluctuations induced by shallow water internal waves

Measured internal waves from the Yellow Sea and the Massachusetts Bay are used as inputs into numerical simulation on acoustic fluctuations. It is shown that the fluctuations induced by large amplitude shallow-water internal waves strongly depend on receiver depth and distance, and exhibit anisotropy. Different acoustic modes have different sensitivities to internal waves. Both acoustic intensity and phase fluctuation spectra are different from the shallow-water IW spectrum, and become much broader. Individual acoustic mode fluctuations directly and clearly correspond to the characteristics of IWs. For shallow water with a strong thermocline, there is a group of acoustic modes, arrival time variation of which is more sensitive to IWs than others. Arrival time of the first mode is most stable.