Scattering coefficients and Doppler spectra of specularly scattered sound from the sea surface

A sea surface scattering experiment has been conducted in shallow water. A narrow beam parametric array, operating over the frequency range 10–30 kHz, projected acoustic energy at a 10° grazing angle to the surface. The reflected and scattered signals were received in the specular direction. Both the source and receiving hydrophone were mounted to underwater towers. Simultaneous with the scattering experiment, the time‐varying wave height of the sea surface was measured by an acoustic technique. Scattering coefficients and Doppler spectra were computed from the scattered quadrature components. Likewise, processing of the wave‐height data yielded rms wave heights and wave spectra. For the measurements, the Rayleigh roughness parameter varied between 4 and 100. The Doppler spectra were Gaussian with bandwidths related to the roughness parameter, and the scattering coefficients ranged from −2 to −10 dB. Familiar physical optic methods were used to model the acoustic data and the Pierson‐Moskowitz spectrum mo...