Understanding complex wind fields with single Doppler Lidar techniques

Scanning Wind Doppler lidars are more and more used for operational applications for which the retrieval of wind vectors and the turbulence quantities at specific points or at high resolution in an area of interest can bring valuable information. For retrieving volume wind data, many techniques can be used to retrieve wind vectors from the combination of radial wind data at different distances and lines of sight, as the well-known Volume Velocity Processing (VVP) technique, developed formerly for Doppler Radars. Although More sophisticated techniques based on the coupling with computational fluid dynamic models exist. e, a processing based on the VVP technique, called the Volume Wind processing (VW) has been developed. This algorithm includes a Single Value Decomposition algorithm that ensures a robust filtering of the retrieved wind data, and then high accuracy and precision. In addition, radial velocity variance (RVV) algorithm has been developped to remove the constant wind speed over a scan to provide fields of turbulent radial wind speeds. Those fields can be averaged and their variances can be computed to determine the averaged turbulent radial wind speeds as well as its deviation.

In this study, the principle and the validation of the VW algorithm will be presented at different sites (offshore, rural, and urban) against reference anemometers will be firstly presented. The bias and precision on 10 minutes averaged wind speed obtained are both about 0.5 m/s. The results reveal that the accuracy is significantly better for winds along lidar beam and precision better for larger samples of instantaneous wind speeds in the averaging time. Finally, the Volume Wind and the Radial Velocity Variance algorithms have then been applied to datasets of several months measured with Windcube Scanning Lidars at two different sites characterized by complex terrain and buildings. The data processed by the algorithms are analyzed to better understand the heterogeneities of the wind fields and its variations in time.