Toward an Efficient and Comprehensive Assessment of Marine Sediments Through Combining Hydrographic Surveying and Geoacoustic Inversion

Acoustic remote sensing techniques are an attractive means for obtaining information on the composition of marine sediments since they have high coverage capabilities and thus allow for efficient surveying. Operating at a wide range of specific frequencies, the acoustic sensors provide insight into the sediment body at different depths. This article suggests an efficient manner to combine high- and low-frequency acoustics for obtaining a comprehensive description of fine-grained sediments in a shallow water environment, as was aimed at by the Maritime Rapid Environmental Assessment/Blue Planet trial (MREA/BP'07). This trial was carried out in the Mediterranean Sea in 2007, employing a variety of acoustic sensors, including echosounders, seismic systems, and dedicated array configurations. In a previous paper (Siemes , IEEE J. Ocean. Eng. vol. 35, no. 4, pp. 766-778), we established a three-dimensional picture of the sediment distribution in the MREA/BP'07 area by associating high-frequency echosounder data with low-frequency seismics. A classification based solely on these hydrographic measurements, however, could not provide the physical properties of the near-surface sediments. In the current article we complement this environmental picture with results from a geoacoustic inversion effort, which do provide information on the actual physical properties, such as sound speed, density, attenuation, and layer thickness. In contrast to carrying out the inversion over the complete area, only a limited number of locations was selected for inversion, to limit the computational efforts. This selection was based on the hydrographic environmental picture obtained in (Siemes , IEEE J. Ocean. Eng. vol. 35, no. 4, pp. 766-778). Inverted sediment properties obtained within similar hydrographic regions confirm the similarity in sediment type among these regions, whereas differences in sediment properties between different hydrographic regions are confirmed as well. Variations in the inversion results within an area with a single sediment type could be attributed to the presence of gas. These results show the suitability of the proposed approach, where backscatter and seismic data discern areas that a priori would differ in their near-surface sediment properties and where geoacoustic inversion assigns actual sediment parameters to these different areas.