High-frequency subcritical acoustic penetration into a sandy sediment

During the sediment acoustics experiment, SAX99, a hydrophone array was deployed in sandy sediment near Fort Walton Beach, Florida, in a water depth of 18 m. Acoustic methods were used to determine array element positions with an accuracy of about 0.5 cm, permitting coherent beamforming at frequencies in the range 11-50 kHz. Comparing data and simulations, it has been concluded that the primary cause of subcritical acoustic penetration was diffraction by sand ripples that were dominant at this site. These ripples had a wavelength of approximately 50 cm and RMS relief of about 1 cm. The level and angular dependence of the sound field in the sediment agree within experimental uncertainties with predictions made using small-roughness perturbation theory.