Combined HF Radar/Drifter Analyses

Surface current measurements from HF radar are becoming increasingly common in coastal regions throughout the world. HF radar measurements ultimately give time-series maps of Eulerian surface current vectors averaged in space and time. However, many applied problems in coastal oceanography require an understanding of currents in a Lagrangian framework, that is, pathways or trajectories. The gridded Eulerian HF radar vectors do not themselves give trajectories, however trajectories can be easily computed by integration. Implicit in the computed trajectories are scales of motion aliased through averaging in space and time. The drifter data serve as a benchmark by which trajectory model skill can be quantified.

Here we illustrate observed drifter tracks along with computed tracks from time maps of HF radar derived velocities. Tracks are computed using a simple fourth order Runge-Kutta scheme (Press et al. 1992) with no diffusive component. Selecting a map below will show the evolution of both the observed and computed trajectories. Tracks are presently being computed with a variety of integration schemes during various times to determine the most optimal way(s) of determining pathways from HF radar measurements for applications such as search-and-rescue, oil spill response and wastewater monitoring.

The following animated figures (time step each 10 minutes) show a single actual drifter track (green) and simulated drifters (pink, which follow the HF radar derived currents shown as magenta vectors) released at the location of the actual drifter every hour. Some of the simulated drifters stop or disappear due to HF radar data gaps.