HF radar surface current estimates using beamforming and direction finding (Beamscan and MUSIC) with a linear array

In this contribution we compare the performance of a Bartlett Beamforming and two direction finding algorithms (Beamscan and a subspace method, MUSIC) for the estimation of surface currents using a linear array radar system. A 7 month data set from two high frequency (HF) radar sites operating at 8.3 MHz in Long Bay, SC are used in this analysis. Radial estimates from each station are compared to each other (along their baseline) and to two in-situ ADCP current measurements. The results show that data availability is reduced when using the direction finding methods, but there is a significant increase in accuracy of the HF radar surface current estimates at large angles from the radar boresight direction. Beamformed radial HF radar surface current estimates compared to in-situ measurements have the highest correlation (R²>0.8) near the radar boresight direction but are reduced significantly (R²=0.02) at 59 degrees from the radar boresight direction. The performance of the direction finding methods is slightly reduced (R²>0.75) near the radar boresight direction but they perform much better than beamforming at the location far from the radar boresight (R²=0.56 and 0.62 for the Beamscan and MUSIC algorithms, respectively). Application of both methods is suggested for increased accuracies in radial velocity estimates especially for installations where side lobe interference reduces the accuracy of the Beamforming method at high angles.