A two-year intercomparison of CW focusing wind lidar and tall mast wind measurements at Cabauw

TL;DR

This study compares two years of wind measurements from a CW focusing wind lidar and a tall meteorological mast at Cabauw, demonstrating high data availability and accuracy, with some errors corrected using auxiliary data.

Contribution

It provides a comprehensive intercomparison of CW focusing wind lidar data with mast measurements, highlighting data quality, availability, and correction methods under various conditions.

Findings

Lidar data availability is 97-98% under typical conditions.

Mean wind speed bias is within 0.1 m/s with high correlation.

Wind direction bias is within 2 degrees, with a 180° error reduced below 2% using correction.

Abstract

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.