Please join us for the following AOS Seminar on Thursday, April 17 at 4:00PM in Spiess Hall Room 330:
Speaker: Peter Franks, Professor of Biological Oceanography, Scripps Institution of Oceanography
Title: Emergent Patchiness in a Swarm of Autonomous Undersea Robots: Depth-Keeping in Internal Waves
Abstract: High-frequency internal waves have been implicated in patch formation and cross-shelf transport of plankton. The patterns of plankton patchiness are consistent with them having a swimming behavior that interacts with the horizontal strain field of the internal waves. However, it is impossible to quantify the swimming behavior of plankton in situ, so a strong test of this hypothesis has remained elusive. So we created our own, robotic plankton. The Autonomous Underwater Explorer (AUE) is a 1.5 liter drifter capable of controlling its buoyancy. It can be tracked acoustically underwater using a long-baseline navigation system. We released a swarm of 16 AUEs programmed to stay at 10 m depth for 5 hours. Analyses of the drifter tracks showed that the large-scale motions were driven by the tide, while smaller-scale motions were driven by high-frequency internal waves. The depth-keeping behavior of the AUEs caused them to form patches associated with the wave crests and troughs, consistent with theory. As far as we are aware, this is the first quantification of patch formation by subsurface “plankton” in situ. This first field test of the AUEs shows that a great deal can be learned about the small-scale, high-frequency dynamics of the ocean using a swarm of buoyancy-controlled drifters.