Underwater acoustic-based navigation towards multi-vehicle operation and adaptive oceanographic sampling

It is important to register oceanographic data into a geo-referenced coordinate system. Knowing the location of the sampling is critical. For a marine robotic network, the location of Unmanned Surface Vessels (USVs) can be measured using a Global Positioning System (GPS), however the navigation of Autonomous Underwater Vehicles (AUVs) is more challenging. In this paper, we present a method for determining the position of underwater vehicles from a moving USV using the relative range information provided by an Ultra-Short Baseline (USBL)/acoustic modem. The navigation method uses an Extended Kalman Filter (EKF) to update the states predicted from a model-based dead-reckoning technique. Since the vehicle model is relative to the surrounding fluid, we have introduced two environmental states in the state matrix. Such a modification allows us to quantify the effects induced by the ocean current on the vehicle's speed. Beyond that, the method uses a limited number of sensors, only attitude sensors and an USBL/acoustic modem, offering an alternative for AUVs without expensive instruments such as a Doppler Velocity Log (DVL) and an Inertial Measurement Unit (IMU). Experiments are conducted to evaluate the range-based navigation method on a hybrid Slocum underwater glider with an USV. As a result from the reference trial, the estimated glider position stays within the error of 15 meters comparing to the measured position of a surface buoy where the glider is attached. In the open-water trial, trajectories estimated from the range-based navigation are compared with dead-reckoning paths and current-compensated dead-reckoning paths (reference). As a result, the distance errors are bounded with the proposed navigation method while the dead-reckoning errors grow without bound.