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Summary of Proposal RES3104

TitleDIRECTCOMPARISON OF SPACEBORNE SAR AND ON-SITE LIDAR MEASUREMENTS OF SMALL-SCALE WINDVARIATIONS AROUND OFFSHORE WIND FARMS
Investigator Jacobsen, Sven - German Aerospace Center (DLR), Remote Sensing Technology Institute
Team Member
Dr. Jacobsen, Sven - German Aerospace Center (DLR), Remote Sensing Technology Institute
Dr. Pleskachevsky, Andrey - German Aerospace Center (DLR), Remote Sensing Technology Institute
Mr. Schneemann, Jörge - Carl von Ossietzky Universität Oldenburg, Institut für Physik, ForWind – Zentrum für Windenergieforschung
SummaryThe increasing popularity of renewableenergy resources has promoted the construction of offshore wind farms,particularly in the German Bight. While the wind farm layout consists of anarray of large turbines, the interrelation of wind turbine wakes with theremaining array is of substantial interest. The downstream spatial evolution ofturbulent wakes is very complex and depends on manifold parameters such as windspeed, wind direction and ambient atmospheric stability conditions. Besides thewake properties of single turbines, the interrelation of adjacent wind farms isa major subject of interest. To complement and validate existing numericalmodels, corresponding observations with high spatial resolution are needed. Over the past four decades, spaceborneremote sensing of sea surface winds with microwave sensors has developed into amature technology. It is now playing an important role in Earth Observation(EO) due to the capability to measure with high spatial coverage and almostunaffected by weather conditions. Hence, the observations are commonly used forthe improvement of numerical weather prediction (NWP). While scatterometersyield only coarse-resolution data, synthetic aperture radar (SAR) has proven tomeasure local wind related sea surface roughness with both, high resolution andwide coverage. On the other hand, earth-bound remotesensing techniques have evolved significantly. Especially Doppler LiDAR hasbecome an important tool for offshore wind energy related research in the lastyears. Ground-based LiDAR windscanners enable to measure vertical wind profilesor horizontal planar scans of the radial wind speed within a range of severalkilometres. While both methods have been successfullyvalidated against meteorological models and in-situ point measurements, weplan a direct comparison of platform based LiDAR measurements and highresolution 2D sea surface wind fields derived from spaceborne SAR. The analysisis further supported by a comparison with data from the numerical meteorologicalmodel COSMO-DE run by the German Weather Service (DWD).Our work willcontain a comparison of a series of simultaneous wind field observations aroundthe offshore wind farms in the North Sea takenwith TerraSAR-X and two scanning long range LiDAR systems. Bothtechniques are compared with a special focus on small scale variations in windfields both, upstream and downstream from the wind facilities. Methods will be developed to account for different measuring heights and scanduration of the two independent datasets will be evaluated regarding the applicability for turbulent atmospheric conditions predominant inthe wake structures downstream of the wind turbines.

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