Adaptive sampling in the Philippine Sea using autonomous profiling floats and FloatCast

This work details a method for manipulating the horizontal position of free-drifting ocean-profiling floats using vertical depth control. Profiling floats are often used to study oceanographic processes of varying spatial and temporal scales. Since deploying floats is logistically demanding and expensive, active floats must collect measurements most relevant to the sampling objectives. To that end, we present the FloatCast framework for managing drift in a fleet of floats via vertical depth control. The FloatCast software selects float dive commands that are anticipated to align best with sampling objectives by combining tools from machine learning, optimization, and feedback control. First, an echo state network is used to generate forecasts of ocean surface flow. These forecasts are used to compute float trajectory predictions for each set of candidate dive commands. The performance of each set of dive commands is then ranked using a mapping error scoring metric, and the highest-ranking command set is provided to the floats for their next dive. Reported here are simulation and real-time experimental results from FloatCast control in the Philippine Sea. The simulation results provide insight into the broader FloatCast methodology; experimental results show that this control framework has promise, though it offers no performance guarantees. Although these floats are inherently underactuated, implementing FloatCast can increase the sampling effectiveness of a float array and, in turn, improve scientific data products.