OVLI-TA: An Unmanned Aerial System for Measuring Profiles and Turbulence in the Atmospheric Boundary Layer

In recent years, we developed a small, unmanned aerial system (UAS) called OVLI-TA (Objet Volant Leger Instrumenté-Turbulence Atmosphérique) dedicated to atmospheric boundary layer research, in Toulouse (France). The device has a wingspan of 2.60 m and weighed 3.5 kg, including payload. It was essentially developed to investigate turbulence in a way complementary to other existing measurement systems, such as instrumented towers/masts. OVLI-TA's instrumental package includes a 5-hole probe on the nose of the airplane to measure attack and sideslip angles, a Pitot probe to measure static pressure, a fast inertial measurement unit, a GPS receiver, as well as temperature and moisture sensors in specific housings. In addition, the Pixhawk autopilot is used for autonomous flights. OVLI-TA is capable of profiling wind speed, wind direction, temperature, and humidity up to 1 km altitude, in addition to measuring turbulence. After wind tunnel calibrations, flight tests were conducted in March 2016 in Lannemezan (France), where there is a 60-m tower equipped with turbulence sensors. In July 2016, OVLI-TA participated in the international project DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa), in Benin. Comparisons of the OVLI-TA observations with both the 60 m tower measurements and the radiosonde profiles showed good agreement for the mean values of wind, temperature, humidity, and turbulence parameters. Moreover, it validated the capacity of the drone to sample wind fluctuations up to a frequency of around 10 Hz, which corresponds to a spatial resolution of the order of 1 m

Development and Qualification of Instrumented Unmanned Planes for Turbulence Observations in the Atmospheric Surface Layer

The development of new observation systems like drones, present an opportunity to measure differently the turbulence in the atmospheric boundary layer. One of the main advantage of the unmanned plane lies in its capacity to fly at very low heights which is not possible with piloted airplanes, and thus to in situ investigate the turbulence in a way complementary to instrumented towers/masts. In the recent years, we have developed in Toulouse (France) two platforms of different size. The first one, called OVLI-TA, is a small unmanned aerial system (UAS) (3kg, payload included). It is instrumented with a 5-hole probe on the nose of the airplane, a Pitot probe, a fast inertial measurement unit (IMU), a GPS receiver, as well as temperature and moisture sensors in specific housings. After wind tunnel calibrations, the drone’s flight tests were conducted in Lannemezan (France), where there is an equipped 60m tower, which constitutes a reference to our measurements. The drone then participated to the international project DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions In West Africa), in Benin. Moreover, another project is carried out about the instrumentation of a so-called “Boreal” drone, which weights 25 kg and can embark 5 kg of sensors and IMU with data fusion. The scientific payload relates to atmospheric turbulence, GNSS reflectometry and gravimetry. In addition, this UAS has a long endurance (up to 10 h) and is more robust to fly in turbulent conditions. We will present the instrumental packages of the two UASs, the results of qualification flights as well as the first scientific results obtained in the DACCIWA campaign. We will also give some examples of envisaged deployment and observation strategy in future campaigns

Qualification de deux avions sans pilote équipés pour l'observation du vent et de la turbulence dans la couche limite atmosphérique

Le développement des drones dans le cadre de la recherche atmosphérique a connu une forte croissance durant ces dernières années en raison de leurs multiples avantages. Les drones constituent un outil performant pour le profilage des paramètres les plus importants de la couche limite atmosphérique (CLA) comme la température, l’humidité et le vecteur vent, ainsi que pour les observations de la turbulence. Les avions instrumentés dédiés aux observations atmosphériques ont été une source d’inspiration pour le développement des charges utiles des drones qui sont des plateformes complémentaires aux systèmes déjà existants comme les tours, les avions instrumentés et les radiosondes, puisqu’ils peuvent échantillonner des zones inaccessibles aux autres plateformes. Nous avons qualifié deux charges utiles pour la mesure du vent et de la turbulence dans la couche limite atmosphérique pour deux drones de différentes tailles. Le premier est un drone de petite taille (3.5 kg y compris la charge utile et une envergure de 2.6 m) nommé OVLI-TA (Objet Volant Leger Instrumenté–Turbulence Atmosphérique). Le second est le drone BOREAL à voilure fixe de taille supérieure (25 kg dont une charge utile jusqu’à 5 kg et une envergure de 4.2 m).L’instrumentation météorologique d’OVLI-TA est composée d’une sonde cinq-trous qui remplace le nez du drone, un tube Pitot pour mesurer la pression statique et dynamique, une centrale inertielle, un GPS, ainsi que des capteurs de température et d’humidité. De plus, l’autopilot Pixhawk a été utilisé pour la navigation. Les calibrations de la sonde cinq-trous ont été réalisées en soufflerie afin de déterminer les coefficients de sensibilité des angles d’attaque et de dérapage. On présente les analyses d’un vol de qualification mené en mars 2016 dans le centre de recherche atmosphérique à Lannemezan qui est équipé d’une tour de 60 m instrumentée et dédiée à la mesure continue des paramètres de la couche limite atmosphérique, ainsi que de vols réalisés en juin et juillet 2016 lors de la campagne de mesure internationale DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa), au Bénin. Cette analyse permet d’évaluer les performances d’OVLITA pour mesurer les valeurs moyennes du vent, de la température et de l’humidité, ainsi que la turbulence. Dans cette évaluation, les observations de la tour de 60 m et des radiosondes ont servi de référence.Les avancées de BOREAL par rapport à OVLI-TA résident dans sa charge utile qui est plus importante, son autonomie de vol qui peut atteindre les 9 heures, et aussi sa capacité de voler dans des conditions météorologiques plus défavorables. Son instrumentation météorologique inclut un GPS et une centrale inertielle, une sonde cinq-trous qui remplace le nez du drone et qui mesure les angles d’attaque et de dérapage, un tube Pitot, et des capteurs de température et d’humidité. Afin de calibrer la sonde cinq-trous, j’ai analysé les données du test en soufflerie et j’ai réalisé des simulations numériques avec le code d’écoulement FLUENT. De plus, le premier vol de qualification de BOREAL effectué en 2018 nous a permis de déterminer la vitesse air optimale du drone à laquelle les vibrations sont significativement réduites à un niveau acceptable. Par la suite, en 2020, une première campagne de mesure a été menée à Lannemezan afin de qualifier les capacités de BOREAL à mesurer le vent et la turbulence et ceci suite à des comparaisons avec la tour instrumentée. Un état détaillé des performances de la plateforme est présenté.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

Observing mean profiles and turbulence in the atmospheric boundary layer with an instrumented unmanned aerial system

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BOREAL-A Fixed-Wing Unmanned Aerial System for the Measurement of Wind and Turbulence in the Atmospheric Boundary Layer

International audienceAn instrumentation package for wind and turbulence observations in the atmospheric boundary layer on an unmanned aerial vehicle (UAV) called BOREAL has been developed. BOREAL is a fixed-wing UAV built by BOREAL company, which weighs up to 25 kg (5 kg of payload) and has a wingspan of 4.2 m. With a light payload and optimal weather conditions, it has a flight endurance of 9 h. The instrumental payload was designed in order to measure every parameter required for the computation of the three wind components, at a rate of 100 s-1, which is fast enough to capture turbulence fluctuations: a GPS-inertial measurement unit (IMU) platform measures the three components of the groundspeed a well as the attitude angles; the airplane nose has been replaced by a five-hole probe in order to measure the angles of attack and sideslip, according to the so-called radome technique. This probe was calibrated using computational fluid dynamics (CFD) simulations and wind tunnel tests. The remaining instruments are a Pitot tube for static and dynamic pressure measurement and temperature/humidity sensors in dedicated housings. The optimal airspeed at which the vibrations are significantly reduced to an acceptable level was defined from qualification flights. With appropriate flight patterns, the reliability of the mean wind estimates, through self-consistency and comparison with observations performed at 60 m on an instrumented tower could be assessed. Promising first observations of turbulence up to frequencies around 10 Hz and corresponding to a spatial resolution to the order of 3 m are hereby presented

Investigation of atmospheric and wake-induced turbulence within the ANR MOMENTA project

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