Applications of High Resolution AUV-based Side Scan Sonar Data for Benthic Habitat Mapping

The use of side scan sonar imaging for benthic habitat mapping can provide detailed images of the seafloor in deep water habitats. Side scan sonar emits sound waves from a transducer on a survey vessel. These waves are scattered by the ocean floor and the returns are received as a time series of intensities. The result is a greyscale image of the seafloor which can be used to identify hard and soft substrates based on the contrasting intensities of these returns. Lighter areas indicate stronger reflection from a hard substrate while darker areas indicate a softer bottom. Side scan sonar data collected via AUV (autonomous underwater vehicle) can provide higher resolution data for deeper areas of the seafloor. One example of such an area is Juan de Fuca Canyon located in Olympic Coast National Marine Sanctuary (OCNMS) in Washington, USA. In April 2018, an AUV pertaining to Pacific Survey Group obtained over 70 square miles of side scan data detailing the benthic bottom types for a section of the canyon floor, which had not been mapped previously. The AUV was fitted with a Kongsberg EM2040 echosounder and a synthetic aperture side scan sonar that together have the capability of recording seafloor information with up to two-centimeter resolution. In June 2019, the raw side scan sonar data was processed in SonarWiz, a commercial application for viewing and editing side scan data that allowed the conversion of the data from its original format into georeferenced images for mapping purposes. Coupling images such as these with multibeam bathymetric data can provide new insight into the unique ecosystems and geology of submarine canyons. The final product is a visual representation (mosaic) of the seafloor that will be used by OCNMS for a variety of purposes including deep sea coral research and the creation of official benthic habitat maps and other products that are used directly by OCNMS and distributed to a variety of sanctuary partners.