Real-Time Ray-Tracing for Underwater Distance Evaluation with Application to Distributed Localization of AUV Teams

The paper deals with distributed acoustic localization of teams of Autonomous Underwater Vehicles (AUVs) and proposes a novel algorithm, Real-TimeRay-Tracing (RT2), for evaluating the distance between any pair of AUVs in the team. The technique, based on a modified formulation of the non-***linear sound-ray propagation laws, allows efficient handling of the distorted and reflected acoustic ray paths. The proposed algorithm can be easily implemented on-board of low-cost AUVs, requiring the presence, on each vehicle, of an acoustic modem and a pair of look-up tables, a-priori built on the basis of the assumed knowledge of the depth-dependent sound velocity profile. On such a basis, every AUV can compute its distance w.r.t. to any other neighbour team member, through time-of-flight measurements and the exchanges of depth information only.