Spatio-Temporal Variability of Boundary Layer Winds within Wind Farms from Truck-Based Mobile Lidar Measurements

Developing a microjoule-class pulsed Doppler lidar (MD) and deploying this compact system on mobile platforms such as aircraft, ships, or trucks opened a new opportunity to characterize the dynamics of large-scale, complex wind flows. The PickUp-based Mobile Atmospheric Sounder (PUMAS) lidar system was recently used during the American Wake Experiment (AWAKEN) to address the general structure of the boundary layer wind and turbulence around wind turbines in central Oklahoma.

Wind speed profiles averaged over PUMAS transects influenced by the nearby operating turbines (waked flow) show a 2-4 m s^-1 reduction compared to mean undisturbed (free flow) wind speed profiles. The differences in vertical velocity variance between waked and free flow were relatively small (0.2-0.5 m² s^-2) for late-morning and daytime convective conditions and increased to (0.5-1 m² s^-2) in the early morning hours. Spatial variability of wind speed was observed in time-height cross-sections at different distances from turbines. The PUMAS measurements from stationary position show good agreement with data from stationary Doppler lidars.

PUMAS dataset from AWAKEN demonstrated the capability of the mobile lidar system to document spatial variability of wind flows at different distances from wind turbines and obtain the quantitative estimates of wind speed reduction in the waked flow. The high-frequency, simultaneous measurements of the horizontal and vertical winds provide a new approach for characterizing the spatiotemporal dynamic of boundary layer winds and for wind farm wake analyses.