Homing by acoustic ranging to a single beacon

Homing and docking capabilities are essential in many autonomous underwater vehicle (AUV) applications. The paper tackles the homing problem, leaving aside the actual docking of the vehicle. Homing is often performed by means of acoustic sensors providing the bearing of the beacon to be reached in the vehicle frame. This measurement, combined with the vehicle's heading, is used directly to steer the AUV towards the goal. The algorithm described in the paper only uses acoustic range measurements to the beacon. The difficulties of this approach are due to the fact that a single range measurement does not completely constrain the beacon's position in the vehicle frame nor does it define the direction to follow. In addition, range measurements are noisy and sometimes spurious, and underwater currents affect dead-reckoning measurements. The AUV has then to maneuver, filter the range measurements and estimate the underwater current in order to maintain an estimation of the beacon's position. The homing procedure consists of obtaining an initial estimate of the beacon's position and of the underwater current components by appropriate maneuvers. The initial estimates are further refined during the actual displacement towards the beacon by means of a Kalman filter.