A Wind Iris 2-beam nacelle LiDAR has been calibrated using the white box and black box approach from the ground. The tests have been carried out at the ECN Wind turbine Test site Wieringermeer with particular reference to meteorological mast 2. Measurements have been taken from the 19th of May 2016 until the 17th of August 2016.
In the white box approach each beam has separately been oriented towards a calibrated sonic anemometer mounted in a meteorological mast at a height of 23m and at a distance of 205m. The results of the comparisons show that the measured mast wind speeds and LiDAR wind speeds compare very well. In addition, the deviations, i.e. the binned differences between the nacelle LiDAR wind speed and sonic wind speed data, do not exceed the set uncertainty limits. With this calibration the wind speed measurements of the Wind Iris nacelle LiDAR with serial number C400114 are traced back to standard units and its uncertainties have been quantified both according to ISO 17025.
In the black box approach the nacelle LiDAR’s central line is oriented towards the mast. It is concluded that the comparison shows more scatter and outliers than what is found for the white box calibration. Here, the two measurement points are separated by a horizontal distance of about 100m at 23m height. Most probably turbulence generated at the surface causes that the wind is less homogeneous at 23m than it is for instance at hub height (80m). Therefore, the black box approach apparently is less suitable at this height.