HF radar observations in the German Bight: Measurements and quality control

Abstract

In the South-Eastern part of the North Sea, known as the German Bight, the Helmholz-Zentrum Gessthacht (HZG, former GKSS Research Center) is currently installing the experimental observation Network “Coastal Observing System for Northern and Arctic Seas” (COSYNA). The main components of COSYNA include in situ instruments, a network of High-Frequency over-the-horizon (HF) radars currently consisting of three “WEllen RAdar” (WERA) systems installed on the islands of Wangerooge and Sylt, and close to the harbour of Büsum, as well as numerical models which are linked to the radar measurements by data assimilation. The WERA HF radar system was developed at the University of Hamburg in 1996. A commercial version is available since 2000. As WERA uses FMCW modulation for range resolution, there is no blind range in front of the system and data are available very close to the shore line. Azimuthal and range resolutions are ±3° and 1.5 km, respectively with a maximum range of 120 km. Ocean current maps are created three times an hour. Operation of the HF radar systems started during summer 2010. The three radial components of the current field as measured by the WERA radars are transfered to a central server at HZG, where they are quality checked and combined to give 2-D current maps. Radial components and 2-D maps are archived in a database and made available to the numerical model system. COSYNA provides a web-based interface to make the 2-D maps, as well as the model results available to the public. This paper describes details of the HF radar network including the procedures to reduce the impact of Radio Frequency Interference (RFI) on the measured ocean current maps and to control the quality of the data.