This paper presents an acoustic localization system for small and low-cost autonomous underwater vehicles (AUVs). Accurate and robust localization for low-cost AUVs would lower the barrier toward multi-AUV research in river and ocean environments. However, these AUVs introduce size, power, and cost constraints that prevent the use of conventional AUV sensors and acoustic positioning systems, adding great difficulty to the problem of underwater localization. Our system uses a single acoustic transmitter placed at a reference point and is acoustically passive on the AUV, reducing cost and power use, and enabling multi-AUV localization. The AUV has an ultrashort baseline (USBL) receiver array that uses one-way traveltime (OWTT) and phased-array beamforming to calculate range, azimuth, and inclination to the transmitter, providing an instantaneous estimate of the vehicle location. This estimate is fed to a particle filter and graph-based smoothing algorithm to generate a consistent AUV trajectory. We describe the complete processing pipeline of our system, and present results based on experiments using a low-cost AUV. To the authors' knowledge, this work constitutes the first practical demonstration of the feasibility of OWTT inverted USBL navigation for AUVs.

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The conditions for maximum power transfer from a source antenna to a receiving antenna are examined when the two antennas are in close proximity. As an example, computed and measured results are described for the power transfer efficiency for two-element Yagi antennas. These results can be used to design matching networks between the antenna and a load such as a voltage multiplier for power transfer in a wireless sensor network. It is concluded that maximum PTE could be obtained by continuously tuning the antenna and matching network as the antenna separation and load conditions change.

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 (≤ 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, oneway 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 µ ± σ = 0.03 ± 1.49 m and µ ± σ = −0.11 ± 3.16 • respectively. These experimental results suggest that piUSBL localization can provide a highly accurate, inexpensive, and lowpower navigation solution for the next generation of miniature, low-cost underwater vehicle.