A multi-user underwater acoustic positioning system - experiments using ASVs and miniature acoustic transceivers

To support the navigation of multiple autonomous underwater vehicles (AUVs) it is highly desirable to have multi-user acoustic positioning based purely upon reception of signals periodically broadcast by georeferenced positioning beacons, analogous to an underwater Global Positioning System (GPS). This paper presents a concept for achieving this using small Autonomous Surface Vehicles (ASV) as beacons in a long baseline (LBL) array. Low hardware complexity and cost is achieved by eliminating the need to maintain accurate synchronisation of underwater nodes or to incorporate high accuracy oven controlled or atomic clocks. The EU Marine Robots (EUMR) project enabled a joint experiment in the Adriatic Sea using 4 H2Omni-X ASVs, developed by the University of Zagreb, equipped with miniature, low cost spread spectrum acoustic modems (NMv3) developed by Newcastle University. Positioning results obtained, and compared with ground truth from GPS, provided a successful validation of this concept and the hardware implementation, achieving mean squared error on position estimates of similar to 1m and graceful deterioration as the receiver moves outside the baselines.