Uncrewed Aerial Vehicle (UAV) measurements of atmospheric boundary layer turbulence.*

A semi-autonomous Uncrewed Aerial Vehicle (UAV) was used to measure atmospheric boundary layer turbulence under variable stability conditions. Measurements were taken both with a five-hole probe capable of resolving all three wind components at a frequency of 50Hz and single-sensor hot-wire probe sampled at 20kHz. The UAV was tasked with flying a "racetrack" trajectory with respect to the ground, with the major axis consisting of straight-line flight over the ground encompassing a distance of 800m. The aircraft positions (pitch, roll and yaw) and their rates were constantly monitored and recorded which, when combined with the five-hole probe data, allowed extracting three wind components. The data from this probe was also used to calibrate the hot-wire probe in-situ, which allowed extension of the frequency content from the five-hole-probe system to higher frequencies. The collected data provides turbulence statistics at high Reynolds number with an advantage of scanning an atmospheric flow by moving through an air mass at velocities higher than the wind. While this method has a great potential, there are no widely-accepted procedures to analyze spatio-temporal measurements of this nature, including application of Taylor's frozen flow hypothesis, and extracting longitudinal and transverse wind components. One challenge is to compensate for a reduced hot-wire sensitivity at variable angles with respect to an air flow. The goal of the current work is to develop and propose a reliable procedure in preprocessing such data and then use it to investigate the structure functions scaling for high Reynolds number atmospheric flows.