Using an interferometric synthetic aperture sonar to inspect the Skagerrak World War II chemical munitions dump site

In a collaboration between the Norwegian Defence Research Establishment (FFI) and the The Norwegian Coastal Administration, a HUGIN autonomous underwater vehicle (AUV) with a high resolution interferometric synthetic aperture sonar (SAS) was brought out to the Skagerrak World War II chemical munitions dump site. It mapped and documented parts of the site and located/relocated 35 shipwrecks. In this paper, we study the SAS technology for such applications. SAS technology have the potential to produce images and maps of very high resolution while maintaining large area coverage rates. There are, however, specific considerations to be taken when mapping and imaging shipwrecks which may be large complex elevated structures. We show data examples from the dump site, both of large shipwrecks and of small objects. We compare SAS images with sidescan images acquired earlier, and with multibeam echosounder data. We find SAS interferometry to be well suited for this type of documentation when operated and processed correctly.