Deriving wind gusts based on Doppler lidar measurements using a fast continuous scan mode

Doppler lidar systems scanning with a Velocity Azimuth Display (VAD) configuration are commonly used to determine profiles of wind speed and direction in the Atmospheric Boundary Layer (ABL, e.g. Päschke et al., 2015). In addition to the mean profile, short-term fluctuations of the wind, such as those that occur in connection with wind gusts, are of great interest and practical relevance.

For Doppler lidar systems of the type “Streamline” (Halo Photonics) we defined and tested a scan configuration which appears suitable for the derivation of wind gusts. In particular, a conical scan mode is used and performed as a so-called fast continuous scan mode (fast CSM) that allows with 3.4s a comparably fast duration for one single conical scan with 10-11 beam directions. Such a fast scan is required to measure wind gusts according to the widely accepted definition of a wind gust (3s moving average; WMO (2018)).

This special configuration introduces challenges to the data processing. Based on the fixed laser pulse repetition rate (10 kHz) of the lidar system comparatively few laser pulses are forming one measurement beam which in turn affect the quality of the radial velocity estimates. For that reason, classical approaches for data filtering (signal-to-noise thresholding, consensus filtering) are not always suitable. We therefore developed an alternative method for processing the raw lidar data.

Measurements from a one-year test operation of a Streamline Doppler lidar in the fast CSM at the boundary layer field site (GM) Falkenberg of the German Meteorological Service (DWD) were used to derive both the mean wind vector and the maximum wind gust for 10-minute averaging intervals. The results were compared with sonic measurements at 90m height. We obtained a very good correlation and RMSD values of ~0.3m/s for the mean wind speed and ~0.64m/s for the wind gusts. Similar results were obtained during a 4-weeks campaign at the “Hamburg Weather Mast” at larger heights (175m and 250m).

Besides these statistical results we will show examples of the gust detection for different weather situations (thunderstorm with cold pool, frontal passage, storm depression, convective gustiness) with particular emphasis on the vertical gust propagation.

World Meteorological Organization (WMO) (2018): Measurement of surface wind. In Guide to Meteorological Instruments and Methods of Observation, Volume I -Measurement of Meteorological Variables, No.8: 196–213, URL:https://library.wmo.int/index.php?lvl=notice_display&id=12407#.ZD7G0c7P1aS (accessed April 2023)

Päschke, E., Leinweber, R., and Lehmann, V. (2015): An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial, Atmos. Meas. Tech., 8, 2251–2266, https://doi.org/10.5194/amt-8-2251-2015