Water column current profile aided localisation combined with view-based SLAM for Autonomous Underwater Vehicle navigation

Survey class Autonomous Underwater Vehicles (AUVs) rely on Doppler Velocity Logs (DVL) for precise navigation near the seafloor. In cases where the seafloor depth is greater than the DVL bottom lock range, transiting from the surface where GPS is available to the seafloor presents a localisation problem since both GPS and DVL are unavailable in the mid-water column. This is traditionally addressed by using acoustic positioning systems, which take extra time to deploy or require a tracking vessel. Such systems increase the costs of operating in deep waters and reduce the flexibility of AUV operations. This paper proposes an alternative approach to navigation in the mid-water column that exploits the stability of current profiles of water columns over short periods of time. Observation of these currents are possible with the ADCP (Acoustic Doppler Current Profiler) mode of the DVL. Results with real data from missions with the Sirius AUV show how the full integration of water column descent with the ADCP, seafloor view-based SLAM (Simultaneous Localisation And Mapping), and ascent to the sea surface with ADCP gives results similar to having continuous bottom lock and shows potential to act as an alternative to acoustic localisation.