Estimates of coherence of low-frequency low-grazing angle sound reflected from the sea surface

Abstract

Sea surface scattering experiments were conducted in which sound from underwater explosives was reflected from the sea surface at grazing angles 5° to 40° and was received by vertically separated sensors of a hydrophone array. The sensor separation varied from l0 to 250 m. The surface-reflected arrivals were isolated and processed to obtain estimates of spatial coherence and reflection-loss spectra for frequencies 20 to 250 Hz. The coherence estimates were obtained as a function of frequency, grazing angle, sensor separation, and bearing for different sea surfaces of low sea state. Simultaneous with the acoustic experiment, ocean wave height time series were measured by three oceanographic data buoys operating in the general region of the experiments. Processing of these data yielded estimates of the ocean wave roughness spectra. Sea surface roughness estimates from the acoustic data were consistent with the measured sea surface roughness. [Work supported by NORDA and Naval Electronic System Command.]