Acoustic propagation in the ocean surf zone

Abstract

Broadband acoustic propagation measurements were conducted during the SandyDuck’97 experiment to provide a means of interpreting noise data taken both within and outside of the surf zone. The source was located outside of the nominal surf zone region at a distance of 470 m from the shore in 6 m of water. The receivers were spaced at 6-m intervals 45 to 183 m offshore in 1 to 3 m of water. Both the source and the receivers were located along a line orthogonal to the shore. The cw line sets were transmitted to obtain a description of the temporal fluctuations in the narrowband propagation induced by the temporal variability of the medium, the surface, and the entrained bubble distribution, as a function of range and frequency. The cw pulses and biphase-modulated PR sequences were transmitted to obtain a description of the spatial and temporal variability of the multipath structure. Measurements show significant time variations even under low surf conditions. The measured results are interpreted through simulations obtained using a FEPE propagation model with near-concurrent estimates of the bathymetry and geoacoustic parameters derived by Fabre and Wilson [IEEE J. Ocean. Eng. 22, 434–444 (1997)]. [Work supported by ONR.]