Mapping horizontal wind speed using a single Doppler Wind Lidar scanning horizontally: a test case over Paris

Scanning Doppler Wind Lidars are used in a variety of applications, thanks to the versatility brought by their scanning head. Their principal output is the wind speed along the lidar beam, termed the radial wind speed. When used for vertical profiling, the horizontal wind speed and wind direction are obtained from a wind field reconstruction algorithm (DBS or VAD) applied to the radial wind speed along several high-elevation lines of sight.

However, for other scanning strategies (i.e., with low elevation or horizontal scans), the use of such algorithms is not common, making the radial wind speed the sole output of the Doppler Wind Lidar. The radial wind speed is more difficult to interpret visually for a human user, harder to compare with numerical models, and requires more work to be used into advanced algorithms.

Thus, we showcase the Volume Wind wind field reconstruction algorithm, capable of reconstructing the horizontal wind speed and wind direction from measurement points taken at the same elevation and varying azimuth.

We present data taken from the PANAME2022 campaign, in which a Doppler Wind Lidar (WindCube Scan 400S) was set up on an 88m-high tower in Paris city. The lidar performs scans at 0° elevation above the urban area of Paris, measuring radial wind speed from within the Urban Boundary Layer.  Then, we create maps of horizontal wind speed and direction, spanning a large part of the Paris urban area, using the Volume Wind wind field reconstruction algorithm.

This allows us to study the influence of the topography on the wind field at the height of the urban canopy. The effect of the bed of the Seine river is of particular interest, as it is thought to be an important ventilation corridor in periods of extreme heat. These results highlight the potential of remote sensors for studying the Urban Boundary Layer, and the added value of advanced processing algorithms.