Qualification Of Two Unmanned Aerial Systems For Wind And Turbulence Observations In The Atmospheric Boundary Layer

The development of unmanned aerial vehicles (UAVs) for atmospheric research during the last years undergoes a remarkable growth all over the world due to their several advantages. They are a new tool for profiling the main parameters of the atmospheric boundary layer (ABL) such as temperature, humidity and wind vector, as well as for turbulence observations. Their development was inspired by instrumented airplanes. In addition, they are complementary to other existing platforms such as instrumented towers and airplanes, and radiosondes, since they can fly in areas unreachable by these other platforms. We have developed two instrumentation packages for wind and turbulence observations in the atmospheric boundary layer for two UAVs of distinct sizes. The first one is a small size UAV (3.5 kg payload included and with a wingspan of 2.6 m) called OVLI-TA (Objet Volant Leger Instrumenté-Turbulence Atmosphérique). The second one is the fixed wing UAV called BOREAL which has a larger size (25 kg including a payload of 5 kg and with a wingspan of 4.2 m).The meteorological instrumental package of OVLI-TA is composed of a five-hole probe that replaces the nose of the drone, a Pitot probe to measure static and dynamic pressure, a fast inertial measurement unit, a GPS receiver, as well as temperature and moisture sensors. Moreover, for autonomous flights the Pixhawk autopilot is used. The wind tunnel calibrations of the five-hole probe were conducted in order to determine the calibration coefficients of the angles of attack and sideslip. I present the analysis of a qualification flight test conducted in March 2016 in Lannemezan, in the atmospheric research center (CRA) equipped with an instrumented 60 m tower, as well as of the flights conducted in June and July 2016 during the international project DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa), in Benin. This study allows evaluating the capacity and performances of OVLI-TA to measure mean values of wind, temperature and humidity, along with turbulence. In this assessment, observations from the 60 m tower and radiosondes were used as a reference.BOREAL's advantages over OVLI-TA lie in its larger payload capacity, its flight endurance that could reach 9 hours, and also its ability to fly in more adverse weather conditions. The developed instrumentation includes a GPS-IMU platform, a five-hole probe replacing the nose of the UAV which measures the angles of attack and sideslip, a Pitot tube, in addition to temperature and humidity sensors. In order to calibrate the five-hole probe, I analyzed the data of wind tunnel test and I used FLUENT software for computational fluid dynamics (CFD) simulations. Furthermore, the first qualification flight test conducted in 2018 allowed us to determine the optimal airspeed of the UAV at which the vibrations are significantly reduced to an acceptable level. Subsequently, in 2020, a first campaign was carried out in Lannemezan in order to qualify the BOREAL capacities to measure wind and turbulence and this following comparisons with the instrumented tower. The UAV's performances are presented in details.