Results from a one-year test of the WindRanger® Doppler Lidar at GM Falkenberg

Doppler lidar systems are nowadays widely used for measuring the 3D wind vector within the atmospheric boundary layer (ABL). Different systems tailored towards different fields of application are commercially available. The WindRanger® is a compact, cost-effective and easy-to-use FMCW lidar for vertical wind profiling across the lowest 200 m metres above ground. It performs continuous velocity-azimuth-display scans of the laser beam at a zenith angle of 10 degrees.

To assess the performance of this instrument, a WindRanger® was operated at the boundary layer field site (in German: Grenzschichtmessfeld, GM) Falkenberg of the Deutscher Wetterdienst (DWD) over a period of 13 months. We have compared the wind measurements with this instrument at a height of 90 m above ground versus sonic data collected at the 99m-tower and (for a sub-period) versus lidar wind data obtained with a pulsed Doppler lidar Streamline (Halo Photonics). Limitations of the WindRanger® measurements occurred in connection with precipitation and with low cloud base heights such that the data had to be filtered accordingly. The comparison provided RMSD values around 0.4 ms⁻¹ for the wind speed and < 5° for the wind direction (after removing a bias due to improper alignment towards North).  

The WindRanger® allows for a time resolution of 0.5 s for one complete scan cycle. This lead us to investigate the possibility to derive wind gusts from the high-resolution time series. We found, however, that the wind speed from single-scan data exhibits a high variation throughout the day and derived gusts exceed the values determined from both the sonic and the Streamline Doppler lidar wind data in the convective boundary layer. This result is attributed to the small zenith angle (10 deg); this implies that the retrieved radial velocity values basically represent the vertical wind vector component which is typically characterized by strong fluctuations under convective conditions.