High-frequency sea surface scattering measurements

Abstract

Measurement and modeling of forward and backscatter from the sea surface are important areas of study in high-frequency acoustics. To validate acoustic scattering models that involve reradiation from the surface and near-surface volume scatterers (e.g., bubbles, biologies), acoustic measurement techniques are required that isolate the scattering mechanisms from multipath effects. In this paper, results from surface scattering measurements that obtained reverberation as a function of grazing angle utilizing both parametric and conventional projectors are presented. Measurements were conducted in shallow waters and the directivity properties of the parametric array isolated the surface scattered path. In the study of surface forward scatter, a new technique has been developed that allows separation of surface scatter and direct path by forming a vertical virtual aperture. This technique may be useful in situations where time resolution (bandwidth) is not sufficient. In terms of reverberation, surface scattering strength measured as a function of grazing angle (in 10-deg increments) will be presented for two different sea state conditions. Also, low grazing angle Doppler shift and spread will be shown as a function of up-wind and cross-wind conditions. These results were obtained in measurements conducted in the shallow waters east of Jacksonville, Florida.