ON THE ACCURACY OF HF RADAR SURFACE CURRENT MEASUREMENTS - INTERCOMPARISONS WITH SHIP-BASED SENSORS

High-frequency (HF) radar systems can provide periodic, two-dimensiona l, vector current estimates over an area approaching 1000 km(2). As th e use of these HF systems has gained wider acceptance, a number of att empts have been made to estimate the accuracy of such systems. However , comparisons of HF radar current estimates with in situ sensors are d ifficult to interpret since HF systems measure currents averaged over an area of similar to 1 km(2) and to a depth of only similar to 50 cm while in situ sensors measure currents at a point and somewhat greater depths (similar to 1 to 10 m). Previous studies of the accuracy of HF radar technology have thus attributed the differences observed betwee n HF radar and in situ sensors to an unknown combination of vertical s hear, horizontal inhomogeneity, in situ instrument errors, and HF rada r system errors. This study examines the accuracy of HF radar current measurements using data from the 1993 High Resolution Remote Sensing E xperiment, conducted off Cape Hatteras, North Carolina. Data from four shipborne in situ current meters are compared with data from an Ocean Surface Current Radar (OSCR), a commercial current-measuring radar. W e attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and b y examining the variation of observed current differences as a functio n of location. The results suggest an upper bound on the accuracy of t he OSCR-derived radial currents of 7 to 8 cm/s.