FINO1 Mast Correction

Lateral speed-up effects, upwind flow retardation and downwind wake effects can be much more pronounced for offshore wind measurement masts than for onshore masts. Combined wind and wave loads require different mast designs, which may result in denser lattices, larger footprints and shorter booms as compared to onshore masts. In order to use such offshore wind measurement data for energy yield assessments, the disturbances caused by the measure ment mast need to be properly addressed. For this, DEWI has developed a mast correction method based on the vanishing vertical wind gradients during very unstable situations, thus enabling a “uniform ambient flow mast correction” (UAM). This mast correction scheme was devised by DEWI in 2007 for the FINO1 offshore wind measurement platform [4]. In 2011, it has been re-assessed for a higher directional resolution (1° instead 10°) and has been extended to all cup and sonic anemometer measurement heights. The mast correction refers to the wind direction measured at FINO1 at 91.5 m LAT and the averaging interval of 10 minutes. During 2009 and 2010, a 1-year Lidar measurement campaign was performed on the FINO1 platform. The comparison with a mast correction based on Lidar data showed high agreement and validated the performance of the UAM method [7]. The UAM method can be used for offshore masts if an undisturbed top anemometer is installed. The method, the correction results and the associated uncertainties for FINO1 are detailed below.