Characterizing Thermodynamic Observations from Unshielded Multirotor Drone Sensors

Abstract. Multirotor drones (also known as small Uncrewed Aerial Systems [sUAS] or small Uncrewed Aerial Vehicles [sUAV]) are being increasingly used in atmospheric research to make measurements of the lower atmosphere, and their use is poised to increase in the future. New opportunities are now emerging for drone atmospheric sensing around smaller instrument footprints and lower sensor weights, such as ride-along applications and drone swarms, which necessitate characterizing the performance of unshielded sensors mounted to drones. In this work, we characterize the accuracy of thermodynamic measurements, specifically temperature and water vapor mixing ratio, based on the sensor position onboard multirotor drones. To assess the influence of the drone mechanics on the measurements, ninety-eight drone flights with eight distinct thermodynamic sensor positions were performed next to an instrumented flux tower and a tethersonde carrying identical sensors, where the tower and tethersonde measurements are assumed as truth. The flights were at least nine minutes in length, and nine of the flights were conducted at night. At the best position, absolute daytime temperature errors were between -0.83 K and +0.61 K at the 95 % confidence interval, while nighttime temperature errors were smaller, ranging from -0.28 K and +0.48 K. Water vapor mixing ratio errors are within -0.22 g kg^-1 and +0.66 g kg^-1. We conclude that measurements in field campaigns are more accurate when sensors are placed away from the main body of the drone and are sufficiently aspirated, such as a position near, but not directly under, a spinning propeller.