Dissipative shallow water internal waves and their acoustical properties

Zhou and colleagues, J. Acoust. Soc. Am., vol.44, p.2042-54 (1991), showed that nonlinear shallow water internal waves (IWs) have the frequency dependent property of enhancing bottom interaction of sound. At preferred frequencies, internal waves can induce the coupling of lower-order waterborne modes to higher order modes, which, in turn, can penetrate more deeply into lossy ocean bottom sediments. In a follow up study Broadhead, J. Acoust. Soc. Am., Submitted (1995), analyzed a simplified example of a shallow water waveguide in which internal waves were incorporated through the use of KdV solitons. A frequency-dependent enhancement of acoustic energy transfer from below the thermocline into the mixed layer was observed from the simulations. Analysis revealed that mode coupling induced by the presence of the internal wave was responsible for the energy transfer. This paper extends that work by including dissipative effects on the IWs, and their concomitant effects on acoustic propagation. Simulations of the effect of dissipation on IWs was accomplished by numerical solution of the KdVB equation. Especially of interest is the effect of IW pulse broadening on the mixed layer resonance. This led to an increase in the resonant acoustic frequency