The effect of a layer of varying density on high-frequency acoustic reflection, forward propagation loss and backscattering strength

Abstract

This report examines the impact that a thin layer of varying density would have on high-frequency reflection, forward loss and backscattering of acoustic plane waves from the seafloor. A functional form for density stratification was found by examination of several high-resolution density profiles obtained from x-ray computed tomography scans of seafloor cores. A solution based on these general profiles was used to estimate the reflection coefficient. The influence of the density profile on reflection loss and backscatter was then calculated using the estimated reflection coefficient. Parameter values used in simulations were obtained from the literature or from the CT scans of cores. It was found that inclusion of a density profile adds a strong frequency dependence to estimates of the reflection coefficient and forward loss. The largest effect on total scattering strength is near normal incidence where returns are dominated by interface scattering. The effect of the density profile on the strength of acoustic returns suggests that care should be taken when using high-frequency systems for measuring sediment properties, especially near normal incidence.