LiDAR observations of offshore winds at future wind turbine operating heights

Combined LiDAR/cup anemometer observations performed in the summer of 2006 of wind speed profiles up to 161 m have been analyzed within an open sea sector at the Horns Rev offshore wind farm. The influence of atmospheric stability on the surface layer wind shear is studied by using a bulk formulation of the Richardson number to derive the Obukhov length from 10 minutes mean temperature and wind speed measurements. The influence of the boundary layer height on the wind speed profile gives a strong over-prediction of the wind speed in stable atmospheric conditions. A length scale model is suggested where the boundary layer height is taken into account. The resulting wind profile agrees well compared to the combined LiDAR/mast profiles in and beyond surface layer.