On Active Current Selection for Lagrangian Profilers

Autonomous Lagrangian profilers are now widely used as measurement and monitoring platforms, notably in observation programs as Argo. In a typical mode of operation, the profilers drift passively at their parking depth before making a vertical profile to go back to the surface. This paper presents simple and computationally-efficient control strategies to actively select and use ocean currents so that a profiler can autonomously reach a desired destination. After briefly presenting a typical profiler and possible mechanical modifications for a coastal environment, we introduce simple mathematical models for the profiler and the currents it will use. We then present simple feedback controllers that, using the direction of the currents and taking into account the configuration of the environment (coastal or deep-sea), is able to steer the profiler to any desired horizontal location. To illustrate the approach, a few results are presented using both simulated currents and real current velocity profiles from the North Sea.