Deriving atmospheric turbulence intensity from profiling pulsed lidar measurements
Abstract. A new method is proposed to provide estimates of the turbulence intensity (TI) from measurements of pulsed lidars (light detection and ranging) employing the Doppler beam swinging technique. This method relies on combining the variances of the line-of-sight (LOS) velocities collected by the five independent beams of the lidars and, as such, is referred to as the variance method. The variance method comes with an explicit removal of the Doppler noise (inherent to the instrument) to the variance of the LOS velocities. Turbulence metrics derived from the variance method are compared to that derived from a standard method, commonly used in the wind energy industry. Reference turbulence measurements are provided by a sonic anemometer mounted on a meteorological mast, installed nearby the lidars. Two configurations of the WindCube v2.1 lidars are proposed: the commercial configuration and a prototype configuration, sampling 4 times faster, thus allowing to capture the turbulent energy of smaller eddies. The standard method applied on wind measurements collected by both configurations shows mean errors in TI estimates of more than 50 %. The application of the variance method on measurements collected by the commercial and prototype configuration drops the mean error to 16.7 % and 13.2 % respectively.
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