ACINN Graduate Seminar - WS 2023/24
2023-11-08 at 12:00 (on-line and on-site)
Use of small uncrewed aircraft systems for lower-troposphere research
Andreas Platis, Jens Bange
Environmental Physics, University of Tübingen, Germany
The atmospheric environment that affects life on earth the most is the lower troposphere, and especially the atmospheric boundary layer (ABL). Most of the physical and chemical interaction of the earth's surface with the atmosphere happens here. Although we feel this interaction every day, many processes in the ABL are unknown, especially in the late afternoon, at night, and in the early morning, when thermal stability of the ABL changes rapidly. More insight into these processes (i.e. a proper physical and mathematical description) leads to a better understanding of the Earth's surface budgets,the propagation of matter and gas, and more reliable forecasts of weather and climate. Regarding applied science and engineering, e.g. this also helps with the understanding of wind turbines and their interaction with the ABL.
For in situ probing of the lower troposphere, very different approaches are available. Meteorological towers and vertical remote sensing systems observe time series of air columns. Ground stations and tethered balloons deliver point measurements. Aircraft provide a mixture of all, depending on the flight strategy: During vertical soundings or slant flight profiles, research aircraft deliver data from air columns. While on a horizontal flight pattern, areas are covered. Spatial data resolution can be very high, and thus research aircraft are able to measure turbulence and turbulent fluxes using eddy covariance (EC). Compared to towers, remote sensing systems, and ground stations, research aircraft can be applied in a very flexible and mobile way, even in remote regions that other systems (maybe apart from satellite observations) cannot reach at all.
While crewed research aircraft are able to carry enormous amounts of scientific equipment, these systems are usually very expensive, with respect to acquisition, operation, and servicing. In contrast, uncrewed aircraft system (UAS) may carry less equipment, but are way less costly and much easier to handle, especially for small research teams e.g. at universities. From the physical point of view, small UAS have the big advantage to disturb the atmospheric flow much less due to their smaller size and weaker propulsion, and thus are much better suited to resolve small-scale turbulent variations of the atmosphere, compared to large research aircraft. Besides, UAS can be operated in remote and dangerous regions where human pilots should not operate. e.g. above active volcanoes, in Saharan dust, or in polar fjords.
Since 1991, starting with the AAI Aerosonde, UAS are in serious operation for meteorological research. Since then, miniaturisation and mass production of almost all required parts – owing to the overall developments on e.g. the computer and smartphone market – the acquisition or self-construction of research UAS became feasible even for smaller and less wealthy organisations like university groups. While electric propulsion and the use of autopilot systems are very common with modern research UAS, the overall designs differ a lot. Two large groups can be defined with respect to aerodynamics and use:
- The very common multicopter rotorcraft, which are very easy to use, widespread, and often referred to as ’drones’. With a typical endurance of not more than 30 minutes and due to their flight principle, these UAS are widely used for vertical profiling, point measurements during hovering, but also very suited for swarm operation.
- The fixed-wing UAS, which are more complicated and demanding in use but can cover much larger distances and altitudes compared to rotorcraft. Also, only fixed-wing UAS are able to measure small-scale turbulence and thus turbulent fluxes, although rotorcraft now enter this research area at least at the larger-scale end.
The Environmental Physics team at the University of Tübingen, Germany (Umphy team) has extensive expertise in conducting measurement campaigns using small research UAS for profiling meteorological quantities, as well as measuring turbulent and non-turbulent transport of momentum, heat, gases, and particles in the ABL in various environments ranging from the Mediterranean, central European landscapes (including complex terrain), to polar environments. Through these campaigns and the related project co-operations, the Umphy team has well established expertise and partnerships in aerospace engineering, numerical flow modelling, environmental physics, and meteorology.
In our presentation we will address the topics mentioned above and in addition show some measurement strategies and results, and give some outlooks from currently conducted UAS research projects in the fields of wind-energy production, validation of remote sensing systems, air quality, and improvement of numerical weather prediction by data assimilation.
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