Turbine-scale wind field measurements using dual-Doppler lidar

摘要

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 60 m meteorological tower and two scanning coherent Doppler lidars. The lidars were configured to perform coordinated dual-Doppler scans surrounding the 60 m 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 60 m 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°), 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 915 MHz 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.