Validating Precision Estimates in Horizontal Wind Measurements from a Doppler Lidar
Rob K. Newsom1, W. Alan Brewer2, James M. Wilczak2, Daniel E. Wolfe2,3, Steven P. Oncley4, and Julie K. Lundquist5,61Pacific Northwest National Laboratory, Richland, WA, 99352, USA 2National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, CO, 80305, USA 3Cooperative Institute for Research in Environmental Sciences , Boulder, CO, 80305, USA 4National Center for Atmospheric Research, Boulder, CO, 80307, USA 5Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, 80309, USA 6National Renewable Energy Laboratory, Golden, CO, 80401, USA
Received: 23 Sep 2016 – Accepted for review: 31 Oct 2016 – Discussion started: 22 Nov 2016
Abstract. Results from a recent field campaign are used to assess the accuracy of wind speed and direction precision estimates produced by a Doppler lidar wind retrieval algorithm. The algorithm, which is based on the traditional velocity-azimuth-display (VAD) technique, estimates the wind speed and direction measurement precision using standard error propagation techniques. For this study, the lidar was configured to execute an 8-beam plan-position-indicator (PPI) scan once every 12 minutes during the 6 week deployment period. Several wind retrieval trials were conducted using different schemes for estimating the uncertainty in the radial velocity measurements. The resulting wind speed and direction precision estimates were compared to differences in wind speed and direction between the VAD algorithm and sonic anemometer measurements taken on a nearby 300-m tower. All trials produced qualitatively similar wind fields with negligible bias, but substantially different wind speed and direction precision fields. The most accurate wind speed and direction precisions were obtained when the radial velocity uncertainty was determined by direct calculation of radial velocity standard deviation along each pointing direction and range gate of the PPI scan. By contrast, setting the radial velocity uncertainty to the radial velocity precision (thereby ignoring turbulence effects) resulted in wind speed and direction precisions that were biased far too low and poor indicators of data quality.
Newsom, R. K., Brewer, W. A., Wilczak, J. M., Wolfe, D. E., Oncley, S. P., and Lundquist, J. K.: Validating Precision Estimates in Horizontal Wind Measurements from a Doppler Lidar, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-312, in review, 2016.