Measurements of the angular dependence of acoustic seafloor scattering in sandy sites.

Abstract

Seafloor scattering measurements are analyzed from a series of experiments (lasting from 3 weeks to 5 months) located in two shallow-water locations near Portsmouth, New Hampshire, USA. The experimental setup consisted of a tripod with transducers (operating at 38, 70, and 200 kHz) mounted ∼2 m above the seafloor and oriented at 17.5° grazing angle. Environmental measurements were obtained using a wave-sensing conductivity, temperature, and depth probe. Seafloor roughness was estimated using stereo imaging techniques on underwater photographs. The measured seafloor scattering strengths were averaged over calm periods between storm events. The overall levels and trends are compared to predictions from the small-slope approximation model. Data-model differences may be due to uncertainty in the model inputs and/or scattering mechanisms not captured in the model. In addition, the results are compared to reported estimates of scattering strength in sand-sized sediments. At a given frequency, grazing angle, and grain size, scattering strengths among all measurements vary up to ∼ 20 dB.