A Flexible Navigation Support System for a Team of Underwater Robots

The primary and somewhat interrelated challenges affecting deployment of Autonomous Underwater Vehicles (AUVs) are navigation and communication. We have developed miniature, agile, easy to carry and deploy AUVs equipped with a suite of sensors for underwater environmental sensing. In this paper, we propose a support system for multiple AUVs where a group of Autonomous Surface Vehicles (ASVs) coordinate to provide external positioning reference. They transmit an acoustic ranging pulse and then broadcast their position using acoustic communication. Communication errors are detected by using a novel approach where data decoding is coupled with navigation. Our system achieves scalability in the number of AUVs by using one-way travel time for ranging and making the AUVs passive receivers. Further, it allows the ASVs to be repositioned during a mission, so that they can provide positioning aid from a closer range. This is an advantage especially in shallow water environments, where range measurement errors increase significantly with increasing distance. We describe our system in detail and evaluate it with simulations based on real data as well as field experiments.