High-frequency scattering from a sand sediment with an overlying mud layer

Abstract

In the spring of 2014, multibeam echo sounder time series data were collected in St. Andrew’s Bay, FL, in an area of the bay where the sand sediment was covered by a mud layer. As part of the environmental characterization at the experiment site, the In-Situ Measurement of Porosity (IMP2) system collected conductivity probe data 25 cm into the seabed along 3 m tracks. The mud layer appears clearly in the conductivity probe data and had a mean thickness of 13 cm. The roughness power spectrum of the sand/mud interface was 10–20 dB higher than that of the mud/water interface and, more significantly, was 5–10 dB higher than that of sand/water interfaces measured in the Gulf of Mexico during the Target and Reverberation Experiment 2013. The mud layer appears to be preserving the roughness of the sand interface, an effect observed during the Sediment Acoustics Experiment in 2004 following the passage of Hurricane Ivan. The impact of both the increased roughness and the presence of the mud on 180–420 kHz scattering will be assessed through data/model comparisons using the sediment properties measured at the experiment site. [Work supported by ONR and SERDP.]