Improving wind speed availability of a six-beam Doppler lidar

Abstract. A simple adaptive variant of the Doppler beam swinging (DBS) method is presented to enhance the availability of wind velocity measurements in profiling lidars. The adaptive method dynamically selects Doppler velocities from beams that have sufficient signal-to-noise ratios (SNRs) in their backscattered signals; then it uses those Doppler velocities for wind velocity reconstruction, rather than relying on the standard approach which discards the entire scan whenever even one beam's backscattered signal does not meet the SNR requirement. The adaptive method was validated in two measurement campaigns at the Østerild wind turbine test field in Denmark using three BEAM 6x profiling lidars from Lumibird. In the first campaign, a lidar measured up to 500 m in proximity to a meteorological mast; in the second campaign, the first lidar was replaced by two other lidar units to increase the maximum measurement range up to 1 km. Validation against cup anemometers and wind vanes at four different heights of the met mast showed excellent agreement for mean wind speed and wind direction, with results similar to those from the standard approach. Availability assessments indicated improvements for all three lidars at high altitudes, showing a maximum increment of 16.9 percentage points over the standard approach. Due to its simplicity, the adaptive method can be implemented in lidar software without requiring any hardware modifications.