Accuracy Assessment of Surface Current Velocities Observed by OSMAR-S High-Frequency Radar System

High-frequency (HF) radar receives the sea echo backscattered from the fluctuating ocean surface to remotely sense ocean surface currents over a large area with a high space-time resolution. To advance our understanding on this technology, we carried out an experiment for verifying the performance of ocean state monitoring and analyzing radar, model S (OSMAR-S) in ocean surface current measurement. The hourly radial currents measured by this radar system show a good agreement with acoustic Doppler current profilers (ADCPs) with correlation coefficients ranging in 0.40-0.93 and root-mean-square-error (rmse) values in 0.11-0.18 m/s. The u/v components of the radar-derived vector currents show a similar deviation from the ADCPs with correlation coefficients varying from 0.56 to 0.93 and rmse values varying in 0.13-0.18 m/s. Also, the bearing offset of this radar system in current extraction is in the range from -11° to 18°. In consideration of the fact that the ideal antenna pattern was used in determining the bearing of the radials, we assume the main source resulting in the bearing offset is the antenna pattern distortion. Thus, a quantitative relation between the antenna pattern distortion factor and the bearing offset has been deduced. With this relation, we estimated the bearing error in the moorings' bearing with the aid of the current information recorded by ADCPs. As expected, the result indicates that the antenna pattern distortion dominates the error of the bearing determination.