Lidar Measurements of Wind Flow through a Rotor-swept Area in Tehachapi Pass

Retrieval of wind fields from a single-Doppler lidar with small azimuthal sectors is challenging. Both simpler retrieval algorithms such as Velocity Azimuth Display (VAD) or Volume Velocity Processing (VVP), and more sophisticated techniques such as Four Dimensional Variational Analysis (4DVAR) using VAD for mean velocities have limitations on small sectors of data. Narrow datasets may result in non-orthogonality and collinearity of basis functions, which causes numerical instability. Although careful inspection of data can reduce the instability, large conditional number computations which use data over small sectors may make results unacceptable [1]. Since estimates of wind velocities retrieved from single Doppler lidar over limited sectors may be of interest (i.e., winds through a single wind turbine or wakes behind buildings), a method to retrieve wind velocity in these situations would be valuable. In this work, we experiment with an algorithm which is able to provide these velocity estimates under the assumption that the wind direction is relatively unchanging or varies linearly over a larger sector, and quasi-2D ridge can have a tendency to homogenize wind direction. The wind direction of the larger neighborhood is obtained from a sectorVAD-like method while magnitudes are allowed to vary fully locally.