Turbine-scale wind field measurements using dual-Doppler lidar

Spatially resolved measurements of microscale winds are retrieved using scanning dual-Doppler lidar and then compared with independent in situ wind measurements. Data for this study were obtained during a month-long field campaign conducted at a site in north-central Oklahoma in November of 2010. Observational platforms include one instrumented 60m meteorological tower and two scanning coherent Doppler lidars. The lidars were configured to perform coordinated dual-Doppler scans surrounding the 60m tower, and the resulting radial velocity observations were processed to retrieve the three-component velocity vector field on surfaces defined by the intersecting scan planes. The dual-Doppler analysis method is described, and three-dimensional visualizations of the retrieved fields are presented. The retrieved winds are compared with sonic anemometer (SA) measurements at the 60m level on the tower. The Pearson correlation coefficient between the retrievals and the SA wind speeds was greater than 0.97, and the wind direction difference was very small (<0.1(o)), suggesting that the dual-Doppler technique can be used to examine fine-scale variations in the flow. However, the mean percent difference between the SA and dual-Doppler wind speed was approximately 15%, with the SA consistently measuring larger wind speeds. To identify the source of the discrepancy, a multi-instrument intercomparison study was performed involving lidar wind speeds derived from standard velocity-azimuth display (VAD) analysis of plan position indicator scan data, a nearby 915MHz radar wind profiler (RWP) and radiosondes. The lidar VAD, RWP and radiosondes wind speeds were found to agree to within 3%. By contrast, SA wind speeds were found to be approximately 14% larger than the lidar VAD wind speeds. These results suggest that the SA produced wind speeds that were too large. Copyright (c) 2013 John Wiley & Sons, Ltd.