A new acoustic technique for remote measurement of the temporal ocean wave spectrum

A method is described that uses low-frequency sound (≲200 Hz) to measure the wave-height variance and the nondirectional temporal wave-height spectrum of a random rough surface. The technique requires a vertically pointing broad-beam acoustic source and a colocated receiver that records the amplitude and phase fluctuations of the backscattered field. When the root-mean-square surface wave-height is much smaller than the acoustic wavelength, the temporal spectrum of the backscattered amplitude and phase fluctuations can be related directly to the nondirectional temporal surface-wave-height spectrum. Typically, surface waves with lengths of a few metres or more can be probed, and the corresponding temporal wave-height spectrum out to frequencies of roughly 1 Hz can be retrieved