Hexarotor UAV for High-Resolution Measurements of Atmospheric Flow and Particles Using Sonic Anemometry and Holographic Imaging*

An advanced hexarotor UAV system has been developed for simultaneous in situ measurements of atmospheric flow and particles. The UAV is equipped with a full-scale ultrasonic anemometer operating at a sampling rate of 20 Hz to characterize atmospheric flow. Concurrently, a multi-resolution holographic particle imaging system measures atmospheric particulate size distribution, with particle size spanning from ~1 µm to 1 mm. A data fusion algorithm has been developed to account for the UAV's constant translation and rotation, integrating sonic anemometer readings with UAV flight control data to accurately determine wind speeds. To address propeller effects on wind measurement, benchmark experiments led to the development of two correction methods: traditional piecewise linear fitting and a frequency-domain-based method. These methods significantly improved accuracy, reducing biases and improving correlation with reference data. The UAV system supports multiple flight modes, enabling the measurement of atmospheric boundary layer profiles, turbulence properties, and particle size distributions. Further development investigated various flight patterns to assess wind profiling accuracy and reconstruct the temporal evolution of the wind field from sparse data. The UAV has been utilized to capture the incoming flow and wake data of a wind turbine, which are critical for optimizing wind farm performance and efficiency. This UAV system demonstrates a robust capability in capturing highly accurate and versatile quantitative data on atmospheric flow and particle characteristics. Its potential applications span various research fields, including offshore wind energy, cloud dynamics, and marine aerosols. The UAV can be deployed in groups, providing more comprehensive data for wind and particle field monitoring across various applications.