Wind shear proportional errors in the horizontal wind speed sensed by focused, range gated lidars

Abstract

The 10-minute average horizontal wind speeds sensed with lidar andmast mounted cup anemometers, at 60 to 116 meters altitude at HØvsØre,are compared. The lidar deviation from the cup value as a functionof wind velocity and wind shear is studied in a 2-parametric regressionanalysis which reveals an altitude dependent relation between thelidar error and the wind shear. A likely explanation for this relationis an error in the intended sensing altitude. At most this erroris estimated to 9 m which induced errors in the horizontal wind velocityof up to 0.5 m/s as compared to a cup at the intended altitude. Thealtitude errors of focused range gated lidars are likely to arisepartly from an unaccounted shift of the weighting functions, describingthe sample volume, due to the range dependent collection efficiencyof the focused telescope. Possibilities of correcting the lidar measurementsboth for wind velocity and wind shear dependent errors are discussed.The 2-parametric regression analysis described in this paper is provento be a better approach when acceptance testing and calibrating lidars.