Improved Current Mapping with HF Radars: Correction for Antenna Pattern Distortion

There are two types of HF radar commercially available for measuring ocean surface currents: narrow-beam phased-arrays and broad-beam direction-finding SeaSondes. Comparison between simultaneous data from the two types of radar has never been made, but quantitative differences have been observed in currents measured by a SeaSonde and a phased-array radar deployed in the same location at different times. We suggest that the differences are caused by antenna distortion due to their nearby surroundings. Pattern measurements on each have shown significant distortions, while analysis algorithms for both systems are based on perfect patterns. We propose methods to remove the effect of antenna pattern distortion from SeaSonde current velocities, and use the resulting current maps to simulate the phased-array results, which do not presently account for antenna pattern distortion. These methods will be applied to currents measured by co-located systems of the two types. We will use the NOAA/ETL SeaSonde operating at the Long Marine Laboratory in Santa Cruz, California and a phased array radar owned jointly by the University of Michigan, Stanford University and ERIM. This will be the first simultaneous comparison of data from the SeaSonde and a phased array.