Coordinated and Collaborative Sampling by Two Long-Range Autonomous Underwater Vehicles

Abstract

Multiple autonomous underwater vehicles (AUVs) working in collaboration can achieve scientific goals more effectively than independently operated vehicles. In this article, we present a case of using two long-range AUVs (LRAUVs) for persistent environmental DNA (eDNA) sampling of a targeted feature. Each LRAUV was equipped with a third-generation environmental sample processor (3G-ESP), a robotic instrument for acquiring and processing water samples for molecular analysis. Each 3G-ESP can collect and process 60 samples. For continuous and persistent eDNA sampling of vertically migrating organisms at a targeted depth layer, we deployed two LRAUVs which alternately triggered the ESP, extending the total time of collecting samples. We developed a method of coordinated sampling by time shift and a collaborative sampling method that uses acoustic handshakes. In the time-shift method, each vehicle switched between two behaviors: sample collection at the targeted depth and spiraling over a large depth range to make contextual measurement. The second vehicle's mission started later than the first vehicle's by a time shift equal to the duration of one sampling event, such that at a given time one vehicle sampled at the targeted depth while the other vehicle spiraled up and down. In the acoustic-handshake method, the two LRAUVs exchanged sample-start and sample-end messages. On receiving vehicle #1’s sample-end message, vehicle #2 triggered a sampling event and transmitted a sample-start message to vehicle #1. Then, vehicle #1 waited for vehicle #2’s sample-end message before triggering the next sampling event, and so forth. The time-shift method is simple, whereas the acoustic-handshake method is accurate and adaptive. Both methods were demonstrated in experiments in Monterey Bay.