Investigation of boundary-layer processes in an Alpine valley with a network of ground-based sensors and UAS

Kurzfassung

Three-dimensional turbulent processes in complex terrain are manifold and crucial for the exchange of energy in the mountain boundary layer. In preparation of the TEAMx observational campaign which is currently planned for the years 2024-2025, a site was identified in 2022 which can be well suited for the investigation of a multitude of thermodynamic processes in Alpine valley systems. The Nafingalm site with a valley base altitude of 1920 m can be reached through the Weer valley, a tributary to the Inn valley in Tirol (Austria). Its size of approximately 2x2 km with an altitude difference of 350-500 m and the North-South orientation with only low vegetation on its 30° slopes towards East, West and South make it a good site to investigate valley wind systems, as well as slope winds. Measuring all the relevant scales within the ABL in the valley requires distributed sensors at the ground, but also aloft, ideally up to the boundary layer height. For this purpose, within the ESTABLIS-UAS project, a fleet of quadrotor uncrewed aerial systems (UAS), is enabled to conduct simultaneous, distributed measurements. The SWUF-3D fleet has already been deployed at the FESSTVaL campaign for calibration and validation and to investigate correlation and coherence in a flat, but heterogeneous terrain. In the pre-campaign towards TEAMx (TEAMx-PC22), which is described here, a goal was to investigate if the systems as used in the SWUF-3D fleet are suitable for deployment in Alpine terrain and if the resolution and accuracy is sufficient to capture valley and slope winds at the site. From 20-28 June 2022, three UAS were operated simultaneously in different configurations and flight strategies for this purpose. Additionally, for a longer period from June through September, ground-based instrumentation was deployed to get a better statistical understanding of the processes in the valley. The flight strategies that were pursued with the UAS were simultaneous vertical profiles along the valley up to 120m above ground, cross-section flights across the valley and distributed hover position flights to capture turbulence statistics. We will show first results of statistics and specific events during the TEAMX-PC22 at the Nafingalm