This project has made great advances at developing a suite of simple,inexpensive, buoyancy­controlled subsurface drifters, and thetechnology necessary to control and coordinate their operation. In thecontext of the project, the robotic swarm has been used in a number ofphysical and biological experiments, including the reconstruction of3­dimensional time­varying flow fields, along with some of its basicphysical characteristics, and the quantification of the effects ofinternal waves on plankton transport and accumulation in the ocean.

Regarding intellectual merit, novel contributions of the project include the development of simultaneous input and state estimation algorithms that use the drifters' motion measurements (depth, acceleration, and position) in the reconstruction of complex ocean flow fields, the design of control and coordination algorithms for drifter depth-keeping and the estimation of linear and nonlinear internal waves, the practical deployment of teams of drifters in the ocean in several experiments to collect real data and test the performance of control algorithms, and the integration of the coordination algorithms with data assimilation and visualization tools.  The project has combined expertise from multiple disciplines (e.g., physical oceanography, marine biology, data fusion and estimation, coordinated control of robotic teams) and scientists and engineers have worked together in the multiple facets involved in successfully sampling oceanographic phenomena at a higher spatial and temporal scale than currently possible.

Regarding broader impacts, the deployment of an AUE swarm has allowed the researchers involved in the project to test, for the first time in situ, scientific hypotheses concerning the coupling of swimming plankton and the high frequency internal wave field and the internal tide. These tests have given new insights into the structure and dynamics of plankton patches on the shelf and an unprecedented view into the physical­-biological couplings of the plankton with the internal wave field.  Our findings show that organisms with simple swimming behaviors can interact with the underlying internal wavefield to experience predictable changes in concentration. Theorganisms can form patches, even without knowledge of any nearby organisms. This could have significant implications for grazing ,infection, and sexual exchange in the plankton. Furthermore, the ability of the drifters to maintain their depth to coordinate with a given temperature is a major achievement as temperature and density are highly correlated in the Southern California Byte and density tracking has long been a goal for physical oceanographers.  Finally, the drifters' ability to intelligently navigate the depth-­dependent flow field and rendezvous at a location for easy retrieval facilitates the execution of deployments and the adoption of the developed technology by other researchers.  

The results from the project are likely to make an impact in testing a suite of scientific biological hypotheses, contributing to a better understanding of ocean flow fields and the biological-­physical couplings occurring underwater.  Multiple exciting applications of the developed oceanographic sampling platform seem now possible, including the estimation of subsurface particle trajectories for ascertaining sewer effluents, the measurement of horizontal and vertical diffusivity, the strain driven by linear and nonlinear internal waves, and the submesoscale vorticity and vertical excursions of the isopycnals. 

The project has also been particularly active in educational activities and the training of a highly skilled workforce.  The postdoctoral, graduate, and undergraduate students involved have been exposed to highly interdisciplinary topics, and have been trained in a collaborative environment, ...

Please report errors in award information by writing to: awardsearch@nsf.gov.