Potential of regridding of FMCW lidar wind profiles to improve data availability

Continuous wave lidars have been widely applied in wind site assessment in recent years. The CW technique uses the adjustment of the beam focus for ranging. A known constraint of this technique is the poor definition of the range weighting function, particularly at upper ranges. In case of inhomogeneous reflectivity distribution, for example caused by low hanging clouds, the center of the scattering volume does not necessarily agree with the center of the adjusted focus range leading to a wrong range allocation of the wind measurements.

As a solution to this fundamental issue, a frequency modulation (FM) of a CW lidar provides independent information of the actual measuring height. The beat frequency of the FMCW lidar depends on the real range of the center of the scattering volume, which may differ from the assumed range based on the focus adjustment. Based on this real range information, the wind profile can be regridded to the expected or defined measuring heights. We will showcase the impact of regridding FMCW wind profiles using a Wind Ranger 200 for cases with inhomogeneous reflectivity distributions and compare the results with a reference pulsed wind lidar.