Remote sensing of surface currents and waves by the HF radar WERA

HF radar is based on the process of backscattering of electromagnetic waves of 10 m to 50 m wavelength from the rough sea surface and can be used to measure surface currents and ocean wave parameters. In contrast to microwave radars, the transmitted electromagnetic wave is guided by the sea surface following the curvature of the Earth beyond the horizon. Depending on the selected working frequency, high ranges up to 200 km can be achieved. The technique has been rapidly developed during the past 25 years. In Germany, the HF radar work started in 1980 by adopting NOAA's CODAR (COastal raDAR) system, introduced in 1977 by Barrick. More recent developments led to an improved design called WERA (WEllen RAdar). This paper describes the different techniques used by CODAR and WERA, their advantages for different applications, the design of WERA and an application at the Dutch coast.