Articles | Volume 9, issue 5
Research article
03 May 2016
Research article |  | 03 May 2016

Evaluation of three lidar scanning strategies for turbulence measurements

Jennifer F. Newman, Petra M. Klein, Sonia Wharton, Ameya Sathe, Timothy A. Bonin, Phillip B. Chilson, and Andreas Muschinski

Abstract. Several errors occur when a traditional Doppler beam swinging (DBS) or velocity–azimuth display (VAD) strategy is used to measure turbulence with a lidar. To mitigate some of these errors, a scanning strategy was recently developed which employs six beam positions to independently estimate the u, v, and w velocity variances and covariances. In order to assess the ability of these different scanning techniques to measure turbulence, a Halo scanning lidar, WindCube v2 pulsed lidar, and ZephIR continuous wave lidar were deployed at field sites in Oklahoma and Colorado with collocated sonic anemometers.

Results indicate that the six-beam strategy mitigates some of the errors caused by VAD and DBS scans, but the strategy is strongly affected by errors in the variance measured at the different beam positions. The ZephIR and WindCube lidars overestimated horizontal variance values by over 60 % under unstable conditions as a result of variance contamination, where additional variance components contaminate the true value of the variance. A correction method was developed for the WindCube lidar that uses variance calculated from the vertical beam position to reduce variance contamination in the u and v variance components. The correction method reduced WindCube variance estimates by over 20 % at both the Oklahoma and Colorado sites under unstable conditions, when variance contamination is largest. This correction method can be easily applied to other lidars that contain a vertical beam position and is a promising method for accurately estimating turbulence with commercially available lidars.

Short summary
Remote sensing devices known as lidars are often used to take measurements at potential wind farm sites. These instruments are however not optimized for measuring turbulence, small-scale changes in wind speed. In this manuscript, the impact of lidar configurations and atmospheric conditions on turbulence accuracy is explored. A new method was developed to correct lidar turbulence measurements and is described in detail such that other lidar users can apply it to their own instruments.