Passive Inverted Ultra-Short Baseline (piUSBL) Localization: An Experimental Evaluation of Accuracy

© 2019 IEEE. The underwater environment poses significant challenges for accurate autonomous underwater vehicle (AUV) navigation. Electromagnetic (EM) waves rapidly attenuate due to absorption by water, thereby preventing the use of traditional EM-based positioning methods such as Global Positioning System (GPS) or visible-light cameras. Consequently, underwater positioning is often performed using systems that operate in the hydro-acoustic frequency range (\leq 10 MHz). Recent work has demonstrated the efficacy of a novel acoustic positioning approach for multi-AUV operations called passive inverted ultra-short baseline (piUSBL) localization-with each vehicle equipped with a time-synchronized USBL array, one-way travel-time (OWTT) range and angle between the AUV and a single acoustic beacon enables multi-AUV navigation relative to the beacon. In this work, a piUSBL system using a five-hydrophone pyramidal array implemented on a WAM-V autonomous surface vehicle (ASV) was used to experimentally gather acoustic measurements and to compare the accuracy of piUSBL localization against ground-truth from a differential GPS unit. This paper provides a comprehensive analysis of the positioning accuracy of the system in a real-world environment, both prior to and after Bayesian filtering, using two independent acoustic beacons for validation. We demonstrate that piUSBL provides acoustic range and angle measurements with errors of about \mu\pm\sigma = 0.03\pm 1.49 \mathrm{m} and \mu\pm\sigma = -0.11\pm 3.16{\circ} respectively. These experimental results suggest that piUSBL localization can provide a highly accurate, inexpensive, and low-power navigation solution for the next generation of miniature, low-cost underwater vehicle