Expanding the DWD network by Doppler lidar systems: ensuring high accuracy during operation

Following recent severe weather events Deutscher Wetterdienst (DWD) expands its operational network by adding vertical profile measurements of wind and humidity. The underlying aim is to spatially and temporally refine the observation base. As a consequence, short-term forecasts and warning capabilities are expected to improve, in particular in case of extreme precipitation events.

In this context, a network of Doppler lidar systems will be installed at 13 automatic weather stations across Germany until 2027. Doppler lidar systems are capable of estimating the three-dimensional wind vector in near real-time within the atmospheric boundary layer and (under favourable conditions) up to a height of 12 km above ground level. Routinely this is achieved by measuring radial wind speed for 4 to 24 equidistantly distributed rays, typically at an elevation angle of 75°.

Over a period of one year, up to six of those systems (WindCube 100S, Vaisala) were operated side-by-side on our test site in Hamburg, Germany. This contribution reports on extensive tests, including tests on positioning accuracy. Given that an error of just 0.15° in elevation corresponds to an under- or overestimation of horizontal wind speed by 1%, positioning accuracy is crucial in an operational set-up. Dedicated test scans known as "flip-tests" are suitable for estimating the magnitude of a potential elevation error, even in a remote set-up. Another potential reason for under- or overestimating radial wind speed lies in the deviation of the beam path from the zenith direction (tilt error). Methods for detecting and quantifying tilt errors based on Doppler lidar measurement data are presented.