  A two-year measurement campaign of the ZephIR 300 vertical profiling
continuous-wave (CW) focusing wind lidar has been carried out by the Royal
Netherlands Meteorological Institute (KNMI) at the Cabauw site. We focus on the
(height-dependent) data availability of the wind lidar under various
meteorological conditions and the data quality through a comparison with in
situ wind measurements at several levels in the 213-m tall meteorological mast.
We find an overall availability of quality controlled wind lidar data of 97 %
to 98 %, where the missing part is mainly due to precipitation events exceeding
1 mm/h or fog or low clouds below 100 m. The mean bias in the horizontal wind
speed is within 0.1 m/s with a high correlation between the mast and wind lidar
measurements, although under some specific conditions (very high wind speed,
fog or low clouds) larger deviations are observed. The mean bias in the wind
direction is within 2 degrees, which is on the same order as the combined
uncertainty in the alignment of the wind lidars and the mast wind vanes. The
well-known 180 degree error in the wind direction output for this type of
instrument occurs about 9 % of the time. A correction scheme based on data of
an auxiliary wind vane at a height of 10 m is applied, leading to a reduction
of the 180 degree error below 2 %. This scheme can be applied in real-time
applications in case a nearby, freely exposed, mast with wind direction
measurements at a single height is available.
