Imaging vent fields: SLAM based navigation scheme for an AUV toward large-area seafloor imaging

This paper proposes a navigation scheme for an AUV to perform large-area imaging of seafloors, especially those of vent fields. The method is based on SLAM (simultaneous localization and mapping) using a profiling sonar and passive acoustic landmarks. Since real-time positioning accuracy of the method is high enough for rough photomosaicing, this method enables an efficient survey with a small overlap and is applicable to seafloors with no visual key for matching. As well as the positioning method, the navigation scheme contains horizontal and vertical path-planning methods, which adapt the vehicle´s path to unprescribed landmarks and rough terrains. The method was implemented in the AUV Tri-Dog 1 and a series of sea experiments have been carried out at Tagiri vent field, Kagoshima bay in Japan since 2006. In 2007, the AUV succeeded in imaging around 3,000 m² of the seafloor and taking micro bathymetry by light sectioning. The relative accuracy of the navigation scheme is estimated to be 0.5 to 1.0 m by comparing photomosaics between dives.