Inverting for bottom parameters in shallow-water soft sediment environments using MBES backscatter strength

Abstract

Shallow water naval operations require detailed knowledge of the environmental properties. In addition to parameters such as water depth, knowledge about the sediment properties is of high importance for a wide range of operations. In this context, the MREA BP'07 experiment was carried out in the Mediterranean Sea in 2007. Measurements employed a large set of sensors, thereby providing all information required to fully describe the environment. This paper focuses on multibeam echosounder (MBES) measurements, which were taken not only to provide information about the water depths, but also to provide the backscatter strength as a function of angle. These backscatter data are employed to infer sediment parameters. To this end, a comparison of measured and modeled backscatter strengths is conducted. Use is made of a model that accounts for both scattering at the water-sediment interface and scattering and scattering at the inhomogeneities in the sediment, i.e. volume scattering. In practice, the measured backscatter strength values are affected by the imperfect MBES calibration. This impedes a direct model-data comparison, unless the effects of miscalibration are eliminated. Therefore, a calibration curve is derived by optimizing spectral strength and volume parameter, according to known mean grain sizes at bottom grab positions. After having corrected the measured backscatter strength for these systematic effects, inversions are carried out to estimate the sediment parameters (grain size, spectral strength, and volume parameter) at various locations in the research area.