Backscattering of Sound from the Sea Surface: Its Measurement, Causes, and Application to the Prediction of Reverberation Levels

Abstract

In many applications of underwater sound, the “reverberation,” or backscattered return, from the sea surface is the limiting background in which the desired echo appears. Little has been known about sea-surface backscattering in spite of its importance to the prediction of reverberation levels in practical applications. Using two transducers—one for transmitting, one for receiving—mounted so as to be rotatable in a vertical plane and suspended from a buoy, measurements have been made of the backscattering of sound pulses from the surface of the sea as a function of grazing angle between 5 and 90 degrees, wind speed between 3 and 18 knots, and pulse length. When converted to a scattering coefficient per unit area, the results provide some hints as to the processes by which sound is scattered by the ocean surface, and give the basic data for computing the reverberation to be expected with transducers of arbitrary beam width and orientation.