TY - JOUR

T1 - Scan strategies for wind profiling with Doppler lidar

T2 - An large-eddy simulation (LES)-based evaluation

AU - Rahlves, Charlotte

AU - Beyrich, Frank

AU - Raasch, Siegfried

N1 - Funding Information: Acknowledgements. The authors would like to acknowledge Lennart Böske for the initial development of the virtual lidar for PALM as well as for providing preceding analysis results. Equally, we would like to thank Katrin Gehrke for providing preceding results and scripts for analysis. The work was supported by the North-German Supercomputing Alliance (HLRN). Funding Information: Financial support. This research has partially been funded by the German Meteorological Service (grant nos. 3057147 and 3059991/21-MIR). The publication of this article was funded by the open-access fund of Leibniz Universität Hannover.

PY - 2022/5/9

Y1 - 2022/5/9

N2 - Doppler-lidar scan techniques for wind profiling rely on the assumption of a horizontally homogeneous wind field and stationarity for the duration of the scan. As this condition is mostly violated in reality, detailed knowledge of the resulting measurement error is required. The objective of this study is to quantify and compare the expected error associated with Doppler-lidar wind profiling for different scan strategies and meteorological conditions by performing virtual Doppler-lidar measurements implemented in a large-eddy simulation (LES) model. Various factors influencing the lidar retrieval error are analyzed through comparison of the wind measured by the virtual lidar with the "true"value generated by the LES. These factors include averaging interval length, zenith angle configuration, scan technique and instrument orientation (cardinal direction). For the first time, ensemble simulations are used to determine the statistically expected uncertainty of the lidar error. The analysis reveals a root-mean-square deviation (RMSD) of less than 1 ms-1 for 10 min averages of wind speed measurements in a moderately convective boundary layer, while RMSD exceeds 2 ms-1 in strongly convective conditions. Unlike instrument orientation with respect to the main flow and scanning scheme, the zenith angle configuration proved to have significant effect on the retrieval error. Horizontal wind speed error is reduced when a larger zenith angle configuration is used but is increased for measurements of vertical wind. Furthermore, we find that extending the averaging interval length of lidar measurements reduces the error. In addition, a longer duration of a full scan cycle and hence a smaller number of scans per averaging interval increases the error. Results suggest that the scan strategy has a measurable impact on the lidar retrieval error and that instrument configuration should be chosen depending on the quantity of interest and the flow conditions in which the measurement is performed.

AB - Doppler-lidar scan techniques for wind profiling rely on the assumption of a horizontally homogeneous wind field and stationarity for the duration of the scan. As this condition is mostly violated in reality, detailed knowledge of the resulting measurement error is required. The objective of this study is to quantify and compare the expected error associated with Doppler-lidar wind profiling for different scan strategies and meteorological conditions by performing virtual Doppler-lidar measurements implemented in a large-eddy simulation (LES) model. Various factors influencing the lidar retrieval error are analyzed through comparison of the wind measured by the virtual lidar with the "true"value generated by the LES. These factors include averaging interval length, zenith angle configuration, scan technique and instrument orientation (cardinal direction). For the first time, ensemble simulations are used to determine the statistically expected uncertainty of the lidar error. The analysis reveals a root-mean-square deviation (RMSD) of less than 1 ms-1 for 10 min averages of wind speed measurements in a moderately convective boundary layer, while RMSD exceeds 2 ms-1 in strongly convective conditions. Unlike instrument orientation with respect to the main flow and scanning scheme, the zenith angle configuration proved to have significant effect on the retrieval error. Horizontal wind speed error is reduced when a larger zenith angle configuration is used but is increased for measurements of vertical wind. Furthermore, we find that extending the averaging interval length of lidar measurements reduces the error. In addition, a longer duration of a full scan cycle and hence a smaller number of scans per averaging interval increases the error. Results suggest that the scan strategy has a measurable impact on the lidar retrieval error and that instrument configuration should be chosen depending on the quantity of interest and the flow conditions in which the measurement is performed.

UR - http://www.scopus.com/inward/record.url?scp=85130510485&partnerID=8YFLogxK

U2 - 10.5194/amt-15-2839-2022

DO - 10.5194/amt-15-2839-2022

M3 - Article

AN - SCOPUS:85130510485

VL - 15

SP - 2839

EP - 2856

JO - Atmospheric measurement techniques

JF - Atmospheric measurement techniques

SN - 1867-1381

IS - 9

ER -