In Situ Uncrewed Aircraft Measurements of Turbulent Kinetic Energy over Heterogeneous Terrain

Abstract Turbulent kinetic energy (TKE) is a key variable in understanding the energy dynamics within the atmospheric boundary layer. Accurate characterization of TKE is crucial for several applications, especially in regions characterized by complexity and heterogeneity. This study investigates the comparison between a moving sensor, an uncrewed aircraft system (UAS), and a stationary sensor, a sonic anemometer, in the heterogeneous terrain of the boundary layer field site Falkenberg (Lindenberg, Germany) operated by the German Weather Service (DWD). The UAS, a multipurpose airborne sensor carrier (MASC-3), was operated during three measurement campaigns in July 2020, June 2021, and November 2022, respectively. The comparison pairs UAS measurements with data collected by a sonic anemometer positioned at a height of 90 m on a meteorological tower. The analysis focuses on careful data processing and precise synchronization of the time series from both sensors, so that the same air mass is taken into account when calculating turbulence statistics. The study examines several parameters that can affect the quality of the comparison. The analysis showed that the bias and scatter between the two sensors are a function of the wind direction: the best agreement was recorded when the wind came from the south, a region of flat terrain (bias of 21%, scatter of 53%). Conversely, less favorable statistics were obtained when the wind blew from a sector between west to north, regions that are predominantly characterized by forest cover (bias of 68%, scatter of 103%). This result illustrates the difficulties of comparing UAS measurements along a 1.5–2.0-km long path with stationary point measurements above a heterogeneous land surface.