One-Way-Travel-Time Hybrid Baseline Navigation for Micro Autonomous Underwater Vehicles

Accurate and reliable navigation is the prerequisite for autonomous underwater vehicles (AUVs) to perform tasks and ensure their safety. Conventional underwater navigation solutions are bulky, expensive, and power-hungry, increasing the AUV size and cost, which stifles the democratization of AUVs, especially for the trend of AUV miniaturization and swarm applications. This article presents a low-cost, power-efficient, and deployable approach to the navigation of micro AUVs. The approach, considered one-way travel-time hybrid baseline (OWTT-HBL) navigation, acoustically consists of two acoustic beacons forming a short baseline (SBL) and a passive inverted ultra-SBL (piUSBL) receiving array on the AUV. Signal broadcasting and acquisition are simultaneously triggered by onboard synchronized clocks for OWTT messaging. The AUV-mounted piUSBL receiving array determines the slant ranges and directions to the SBL beacons through matched filtering and array beamforming. An extended Kalman filter (EKF) state estimator is derived to fuse the acoustic range-angle measurements and the heading angular rate from a microelectromechanical system inertial measurement unit, providing the AUV coordinates and heading angles. A series of field experiments with a micro AUV were compared against the differential-GPS-recorded ground truth and a long baseline system, demonstrating the navigation capabilities. Field results show that the reported OWTT-HBL possesses an accuracy comparable to existing methods while showcasing the great potential for micro AUV navigation and multi-AUV systems.