Measurement and modeling of sound penetration into sandy sediment: Absolute pressure levels

Abstract

As part of the SAX99 high-frequency sediment acoustics experiment, a buried array was used to measure the pressure field in a sandy sediment with sources in the water column. The sediment was a medium sand with pronounced directional ripples. The buried array consisted of five vertical subarrays of six elements each spanning a horizontal aperture of approximately 30 cm and a vertical aperture of approximately 45 cm. Sources operating over the frequency range 11–50 kHz were moved to obtain various propagation directions relative to the ripple field with ranges and elevations that provided incident grazing angles both larger and smaller than the 30-deg critical angle. Signal levels measured by the buried hydrophones were compared with calculations based on a fluid sediment model and small-roughness perturbation theory, with both directional ripple and small-scale isotropic roughness. Under the assumption that hydrophone sensitivity in-sediment is the same as the value measured in water, data-model comparisons show similar azimuthal dependence and agree in absolute level to within about 2 dB for above-critical incidence and about 3 dB for below-critical incidence. [Work supported by ONR.]