Intelligent Buoys for Aiding AUV Navigation Under the Ice

In-situ measurements under the sea-ice are important to understand the rapid climate changes that are occurring in the Arctic region. Autonomous Underwater Vehicles (AUVs) are suited for this application due to its large spatial and temporal coverage and resolution. However, AUV operations under sea-ice in the Arctic are especially challenging due to degraded navigation, limited communication, and the inability to return to the surface during the mission. This paper presents an intelligent buoy network designed to aid AUV navigation during operations under the ice. The navigation buoys are equipped with Global Navigation Satellite Systems (GNSS) and acoustic modems that are used to communicate with the AUV. A Single Transponder Navigation (STN) algorithm designed by the Norwegian Defence Research Establishment (FFI) and Kongsberg Maritime (KM) named Underwater Transponder Positioning (UTP) is used to update the AUVs navigation system during the mission. In addition to the design of the buoys, the paper presents a non-singular horizontal position representation called n-vector and its use for ice-relative guidance and navigation. The method is verified through a simulation study using the FFI/KM navigation processing suite, NavLab, where the drift of the buoys are based on ice drift data from a simulation and forecasting tool for AUVs. The simulations show that the UTP algorithm with moving transponders has low errors for all the tested measurement rates due to high-end inertial navigation. For the lowest tested UTP update rate of 1/120 Hz the RMS errors for x and y-positions are 1.02 m and 1.96 m, respectively, with corresponding standard deviations of 1.00 m and 1.81 m.