Joint offshore wind turbine wake monitoring with spaceborne SAR and in-situ Lidar measurements

Abstract

The increasing popularity of renewable energy resources has promoted the construction of offshore wind parks e.g. in the North Sea. While the wind park layout consists of an array of large turbines, the interrelation of turbine wind wakes with the remaining array is of substantial interest. The downstream spatial evolution of turbulent wind wakes is very complex and depends on manifold parameters such as wind speed, wind direction and ambient atmospheric stability conditions. To complement and validate existing numerical models, corresponding observations are needed. While in-situ measurements with e.g. anemometers provide a time-series at the given location, the merits of ground-based and space- or airborne remote sensing techniques are indisputable in terms of spatial coverage. Active microwave devices, such as Scatterometer and Synthetic Aperture Radar (SAR), have proven their capabilities of providing sea surface wind measurements and particularly SAR images reveal wind variations at a high spatial resolution while retaining the large coverage. The new generation of X-Band SAR satellites can obtain imagery with unprecedented resolution of up to 1m. We present the application of high resolution TerraSAR-X (TS-X) X-band SAR data for the investigation of wind turbine wakes at North Sea wind parks. For our studies, we apply the recently developed X-Band wind field algorithm XMOD2 and compare the derived wind parameters to on-site LIDAR measurements and meteorological information from the FiNO1 scientific platform in the Alpha Ventus array. Our study proves that SAR-derived wind fields are a powerful and reliable tool to observe and quantify turbine wind wake properties and dimensions. Implementation of such findings into models can optimize short-term power production predictions and facilitate scheduling of on-site construction work with regard to safety implications.