A comparison of surface current fields derived by beam forming and direction finding techniques as applied by the HF radar WERA

HF radar in oceanography makes use of backscattering of electromagnetic waves of 10 m to 50 m wavelength from the rough sea surface to measure surface current and ocean wave parameters. In Germany, the work on ground wave HF radar started in 1980, adopting NOAA´s CODAR (COastal raDAR). Recent developments within the European project SCAWVEX (Surface Current And Wave Variability Experiment) lead to a new design called WERA (WEllen RAdar). In Spring 1996, two WERA and CODAR systems have been deployed north and south the Rhine mouth at the Dutch coast. While CODAR uses a four-element squared receive antenna array and direction finding technique for azimuthal resolution, WERA in addition can be configured to use a linear array and beam forming. As both systems have been operated simultaneously at the same location, comparisons of the surface current fields measured by the different systems and algorithms are possible. By defining an absolute quality criterion based on spectral analysis of current time series, limitations in the direction finding algorithm concerning ship traffic can be identified