Scattering of sound into the seafloor waveguide.

Abstract

Data from seafloor arrays indicate that seafloor noise at frequencies greater than 0.5 Hz propagates as fundamental and higher mode interface waves (Schreiner and Dorman, 1990). For much of this frequency range, the phase velocity of these waves is less than the acoustic velocity in water, so the wave is weakly excited by sources in the water column. Correlations between seismic noise and local wind and swell suggest that, at least at frequencies greater than 0.05 Hz, most of the noise originates at the sea surface, leaving one with the problem of connecting the apparent cause (swell and windwaves) with the effect (seafloor noise). The most plausible explanation is that scattering at or near the seafloor couples energy from the high-velocity modes to the interface waves. Several mechanisms are possible. Scattering at rough surfaces (Kuperman and Schmidt, 1989), volume scattering caused by velocity variations (Dorman etal., 1991), and mode coupling through anelasticity are all candidates. [Work supported by ONR.]