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Results of operational sea-wave monitoring with radar gauges

 

Sebastian Rütten, Stephan Mai, Jens Wilhelmi, Theodor Zenz, Hartmut Hein, Ulrich Barjenbruch

New developments off the German coasts, like offshore wind farms, require operational monitoring of waves nearby such offshore structures. Therefore, the German Federal Institute of Hydrology – BfG (in cooperation with the German Federal Waterways Administration – WSV) developed a low-cost, non-contact monitoring system based on a single radar sensor. This system has been in operation at the gauge “Lighthouse Alte Weser” in the estuary of the rivers Jade and Weser since 2006 (see Figure 1). A short description of the measuring system and the analysis of wave parameters is given. The focus of the paper is on the exceedance probabilities of wave parameters (wave height and wave period) and their correlation to wind statistics. Transfer functions of wind speed to wave parameters are determined for different wind directions and uncertainties of this transfer are estimated. The transfer functions are used to derive predictions of possible changes in wave parameters at the “Lighthouse Alte Weser” due to future changes in wind statistics as calculated by regional climate models.

 

So far, it is only possible to monitor wave heights and wave periods at “Alte Weser”. To enlarge the capability towards monitoring of wave direction, an array of at least three radar sensors is now under development (in cooperation with the German Federal Maritime and Hydrographic Agency – BSH). First experiences with this radar array are presented. Finally, possible disturbances of wave measurements by the offshore structure itself are discussed.