Simultaneous Tracking and Sampling of Dynamic Oceanographic Features with AUVs and Drifters

We present AUV survey methodologies to track and sample an advecting patch of water. Current AUV-based sampling rely primarily on geographic waypoint track-line surveys that are suitable for static or slowly changing features. When studying dynamic, rapidly evolving oceanographic features, such methods at best introduce error through insufficient spatial and temporal resolution, and at worst completely miss the spatial and temporal domain of interest. In this work, we extend existing oceanographic sampling methodologies to perform Lagrangian observation studies to sample within the context of an advecting feature of interest. We use GPS-tracked Lagrangian drifters to tag a patch of interest, and utilize its periodic position updates to make an AUV perform surveys around it as it gets advected by ocean currents. Two approaches are described and tested in two field trials in 2010 a one day experiment in June, followed by a five-day offshore experiment in September. Results from the experiments are presented along with the analysis of the sources of error.