Closed-Loop Single-Beacon Passive Acoustic Navigation for Low-Cost Autonomous Underwater Vehicles

Accurate localization is critical for a robotic vehicle to navigate autonomously. Conventional autonomous underwater vehicles (AUV s) typically rely on an inertial navigation system (INS) aided by a Doppler velocity log (DVL) in order to reduce the rate of positional error growth of dead-reckoning to a level suitable for reliable navigation underwater. The size, cost, and power requirements of these systems result in vehicles that are prohibitively large and expensive for multi-AUV operations. In this work we present the first results of closed-loop experiments using a miniature, low-cost SandShark AUV and a custom-designed, inexpensive acoustic system first described in our previous work. Results are validated using an independent LBL system, and indicate that our approach is suitably accurate to enable the self-localization of such AUVs without the use of an expensive DVL-aided INS. Self-localization is performed by obtaining acoustic range and angle measurements from the AUV to a single acoustic beacon using a vehicle-mounted passive hydrophone receiver-array, and fusing these measurements using a particle filter. A critical aspect of our approach that allows for real-time, closed-loop operation is the close coupling of conventional phased-array beamforming and particle filtering - this implementation detail reduces the computational complexity associated with our previously described two-stage beamforming plus particle filtering process, and consequently also enables an increase in particle count and an improvement in navigational accuracy. Experimental results are provided for two cases: first, absolute navigation in the case where the beacon is fixed at a known position; and second, relative navigation with a moving beacon, a novel operating paradigm for AUVs which promises to enable multi-AUV operations while maintaining bounded navigation error.