A near-real-time, high-resolution, ocean-surface-current mapping system

Two-dimensional synoptic-scale ocean surface current fields would be a useful component of an Integrated Ocean Observing and Prediction System. A NOAA-Navy partnership funded by NOPP has shown that a pair of over-the-horizon (OTH or skywave) radars can produce vector surface current maps in the deep ocean with spatial resolution of 10-15 km over areas greater than 10⁵ km² in near-real time. As an example, we show the complexity and time variability of the surface flow into the Gulf of Mexico through the Yucatan Channel. Mesoscale eddies are a recurring feature in the channel, and strong southward flow is present on its east side about half the time. These features are qualitatively confirmed by the tracks of surface-drifter buoys deployed during the Year of the Ocean. Comparisons of these radar-derived currents with satellite altimetry-derived geostrophic currents give a correlation coefficient of 0.78. Limited radar access led us to examine model-based spectral estimators to see if more ocean area could be scanned in the time allotted. Using simulations, we found the most significant advantage of the model-based methods was a reduction in the variability (standard deviation) of the resulting current estimates. In a parallel effort, we examined the use of high-resolution, adaptive beamforming methods with the intent of reducing the size of the needed antenna. These preliminary results suggest that smaller, less costly (by a factor of 1/4), antenna arrays could be built for a dedicated ocean observing radar system. One proposed two-radar configuration could cover the entire Gulf of Mexico and the hurricane approaches to the US East Coast.