SAR Wind Mapping

Synthetic Aperture Radar (SAR) satellite observations are used in the mapping of offshore winds. This is in particular relevant for wind energy. Offshore wind farms are established in several countries. Offshore winds are poorly known due to the high cost of installation and maintenance of masts. Offshore wind resource statistics based on SAR show results with standard error around 1.1 m s-1. When using around 100 images, the results appear to be adequate in pre-feasibility wind engineering work. The study involved around 100 SAR images from ERS and Envisat, and winds are obtained from application of the CMOD-geophysical model functions. Winds from QuikSCAT are also compared to mast observations and the results are good, yet this data type does not directly cover the near-coastal region in which most wind farms are located. Finally, SAR observations from satellite and airborne SAR, the E-SAR of the German Aerospace Center DLR, have been retrieved and analysed near a large offshore wind farm. The results quantify the shadowing (wake) effect behind the wind farm. This is relevant to quantify as wind farms in clusters ‘steal’ wind from others as a function of wind direction and wind speed. The SAR-based results demonstrate wind farm wakes to extend more than 20 km downstream of a wind farm in certain atmospheric conditions. This is not (yet) modelled in wake models that typically give results from 5 to 10 km downwind.