Backseat driver architecture to passively follow sperm whales by their voices with an autonomous underwater glider

Passive acoustic monitoring (PAM) of marine mammals is essential for biodiversity monitoring and communication studies. Tracking animals in situ further enables behavioral investigation. Monitoring from boats, tags, or moorings is limited by the durability of tracking, whereas underwater gliders offer potential for long-term PAM-based tracking. In this paper, we present the design details of backseat driver operations on such a glider. The backseat driver employs acoustic detection, source separation, and angle of arrival estimation of sperm whale (Physeter macrocephalus) echolocation clicks from a four-element hydrophone array mounted on top of a customized Project CETI-SeaExplorer glider. The measurements are used to change the bearing angle of the underwater glider in real time, allowing it to react to the presence of sperm whales and follow them. The glider is a passive system with no radiated noise except when changing buoyancy (a few seconds roughly every hour), and its distance from the whales is above 100 m to have minimal impact on whale behavior. We discuss the operation and connectivity of the backseat driver to the SeaExplorer glider's main computer and how estimation results are shared with the user upon surfacing. While long-term whale monitoring is left for future work, our results from a controlled sea experiment demonstrate the backseat driver operation and show performance in terms of response latency to commands, and results from a field trial off Dominica show the backseat driver source separation capabilities. The code and data for this experiment are open source.