Towards Vertical Wind and Turbulent Flux Estimation with a Fleet of UAS in the Atmospheric Boundary Layer

Kurzfassung

Vertical wind velocity and its fluctuations are essential to determine turbulent fluxes and scaling parameters for ABL processes. Without the infrastructure of meteorological masts and above applicable heights for such masts, in-situ point measurements of the three-dimensional wind vector are hardly available. We present a method to obtain the three-dimensional wind vector from avionic data of small multicopter unmanned aircraft systems (UAS). To achieve a good accuracy in both, average and fluctuating parts of the wind components, calibrated motor thrust and measured accelerations by the UAS are used. The SWUF-3D (Simultaneous Wind measurement with Unmanned Flight systems in 3D) fleet consists of 35 such UAS and was first deployed at the Meteorological Observatory Lindenberg - Richard Aßmann-Observatory (MOL-RAO) of DWD in association to the FESSTVaL campaign. With more than 1000 single flights, the system was validated against sonic anemometers at the 99-m mast in 2020 and 2021. In a validation campaign, in comparison to sonic anemometers on a 99-m mast, accuracies below 0.2 m s-1 are achieved for the mean wind components and below 0.2 m2 s-2 for their variances. The spectra of variances and covariances show good agreement with the sonic anemometer up to 1 Hz temporal resolution. A case study of continuous measurements in a morning transition of a convective boundary layer with five UAS illustrates the potential of such measurements for ABL research. Most recently, a fine-wire resistance thermometer was added to the setup, which allows temperature measurements much faster than standard sensors. Fast response measurements of temperature and vertical wind allow the calculation of sensible heat flux additionally to the Reynolds stresses. Within the project ESTABLIS-UAS (Exposing Spatio-temporal structures of Turbulence in the ABL with In-Situe Measurements by UAS, funded by the European Union), the SWUF-3D fleet will be enhanced to allow operation in larger areas and in complex terrain. A fleet of up to 100 UAS shall be deployed during TEAMx (Multi-scale transport and exchange processes in the atmosphere over mountains, programme and experiment) in 2024