Search

The aim of the investigation was to obtain practical experience and first results from the measurement of highly dynamic processes in the flow around multicopters and their structural reactions. During initial flight tests of a newly developed multicopter UAS (uncrewed aircraft system, 4 rotor configuration) with 25 kg maximum take-off weight a high frequency data acquisition system with different sensors was flying piggyback. Already existing sensors were used, as no funding for dedicated additional payload was available. Sensors were concentrated at one rotor arm. The data acquisition was limited to 8 channels, so different sensor combinations were flown in experimental configurations. Trajectories followed the needs for the multicopter flight testing and were not tailored for this investigation.

Year-round observations of the physical snow and ice properties and processes that govern the ice pack evolution and its interaction with the atmosphere and the ocean were conducted during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition of the research vessel Polarstern in the Arctic Ocean from October 2019 to September 2020. This work was embedded into the interdisciplinary design of the 5 MOSAiC teams, studying the atmosphere, the sea ice, the ocean, the ecosystem, and biogeochemical processes. The overall aim of the snow and sea ice observations during MOSAiC was to characterize the physical properties of the snow and ice cover comprehensively in the central Arctic over an entire annual cycle. This objective was achieved by detailed observations of physical properties and of energy and mass balance of snow and ice. By studying snow and sea ice dynamics over nested spatial scales from centimeters to tens of kilometers, the variability across scales can be considered. On-ice observations of in situ and remote sensing properties of the different surface types over all seasons will help to improve numerical process and climate models and to establish and validate novel satellite remote sensing methods; the linkages to accompanying airborne measurements, satellite observations, and results of numerical models are discussed. We found large spatial variabilities of snow metamorphism and thermal regimes impacting sea ice growth. We conclude that the highly variable snow cover needs to be considered in more detail (in observations, remote sensing, and models) to better understand snow-related feedback processes. The ice pack revealed rapid transformations and motions along the drift in all seasons. The number of coupled ice–ocean interface processes observed in detail are expected to guide upcoming research with respect to the changing Arctic sea ice.

International audience; With the Arctic rapidly changing, the needs to observe, understand, and model the changes are essential. To support these needs, an annual cycle of observations of atmospheric properties, processes, and interactions were made while drifting with the sea ice across the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. An international team designed and implemented the comprehensive program to document and characterize all aspects of the Arctic atmospheric system in unprecedented detail, using a variety of approaches, and across multiple scales. These measurements were coordinated with other observational teams to explore crosscutting and coupled interactions with the Arctic Ocean, sea ice, and ecosystem through a variety of physical and biogeochemical processes. This overview outlines the breadth and complexity of the atmospheric research program, which was organized into 4 subgroups: atmospheric state, clouds and precipitation, gases and aerosols, and energy budgets. Atmospheric variability over the annual cycle revealed important influences from a persistent large-scale winter circulation pattern, leading to some storms with pressure and winds that were outside the interquartile range of past conditions suggested by long-term reanalysis. Similarly, the MOSAiC location was warmer and wetter in summer than the reanalysis climatology, in part due to its close proximity to the sea ice edge.The comprehensiveness of the observational program for characterizing and analyzing atmospheric phenomena is demonstrated via a winter case study examining air mass transitions and a summer case study examining vertical atmospheric evolution. Overall, the MOSAiC atmospheric program successfully met its objectives and was the most comprehensive atmospheric measurement program to date conducted over the Arctic sea ice. The obtained data will support a broad range of coupled-system scientific research and provide an important foundation for advancing multiscale modeling capabilities in the Arctic.

International audience; As part of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) project, extensive in-situ measurements of the southern West African atmospheric boundary layer (ABL) have been performed at three supersites Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria) during the 2016 monsoon period (June and July). The measurements were designed to provide data for advancing our understanding of the relevant processes governing the formation, persistence and dissolution of nocturnal low-level stratus clouds and their influence on the daytime ABL in southern West Africa. An extensive low-level cloud deck often forms during the night and persists long into the following day strongly influencing the ABL diurnal cycle. Although the clouds are of a high significance for the regional climate, the dearth of observations in this region has hindered process understanding. Here, an overview of the measurements ranging from near-surface observations, cloud characteristics, aerosol and precipitation to the dynamics and thermodynamics in the ABL and above, and data processing is given. So-far achieved scientific findings, based on the dataset analyses, are briefly overviewed.

Unmanned aerial systems (UAS) fill a gap in high-resolution observations of meteorological parameters on small scales in the atmospheric boundary layer (ABL). Especially in the remote polar areas, there is a strong need for such detailed observations with different research foci. In this study, three systems are presented which have been adapted to the particular needs for operating in harsh polar environments: The fixed-wing aircraft M 2 AV with a mass of 6 kg, the quadrocopter ALICE with a mass of 19 kg, and the fixed-wing aircraft ALADINA with a mass of almost 25 kg. For all three systems, their particular modifications for polar operations are documented, in particular the insulation and heating requirements for low temperatures. Each system has completed meteorological observations under challenging conditions, including take-off and landing on the ice surface, low temperatures (down to &minus, 28 ∘ C), icing, and, for the quadrocopter, under the impact of the rotor downwash. The influence on the measured parameters is addressed here in the form of numerical simulations and spectral data analysis. Furthermore, results from several case studies are discussed: With the M 2 AV, low-level flights above leads in Antarctic sea ice were performed to study the impact of areas of open water within ice surfaces on the ABL, and a comparison with simulations was performed. ALICE was used to study the small-scale structure and short-term variability of the ABL during a cruise of RV Polarstern to the 79 ∘ N glacier in Greenland. With ALADINA, aerosol measurements of different size classes were performed in Ny-&Aring, lesund, Svalbard, in highly complex terrain. In particular, very small, freshly formed particles are difficult to monitor and require the active control of temperature inside the instruments. The main aim of the article is to demonstrate the potential of UAS for ABL studies in polar environments, and to provide practical advice for future research activities with similar systems.

The combination of two well-established methods, of quadrocopter-borne air sampling and methane isotopic analyses, is applied to determine the source process of methane at different altitudes and to study mixing processes. A proof-of-concept study was performed to demonstrate the capabilities of quadrocopter air sampling for subsequently analysing the methane isotopic composition δ13C in the laboratory. The advantage of the system compared to classical sampling on the ground and at tall towers is the flexibility concerning sampling location, and in particular the flexible choice of sampling altitude, allowing the study of the layering and mixing of air masses with potentially different spatial origin of air masses and methane. Boundary layer mixing processes and the methane isotopic composition were studied at Polder Zarnekow in Mecklenburg–West Pomerania in the north-east of Germany, which has become a strong source of biogenically produced methane after rewetting the drained and degraded peatland. Methane fluxes are measured continuously at the site. They show high emissions from May to September, and a strong diurnal variability. For two case studies on 23 May and 5 September 2018, vertical profiles of temperature and humidity were recorded up to an altitude of 650 and 1000 m, respectively, during the morning transition. Air samples were taken at different altitudes and analysed in the laboratory for methane isotopic composition. The values showed a different isotopic composition in the vertical distribution during stable conditions in the morning (delta values of −51.5 ‰ below the temperature inversion at an altitude of 150 m on 23 May 2018 and at an altitude of 50 m on 5 September 2018, delta values of −50.1 ‰ above). After the onset of turbulent mixing, the isotopic composition was the same throughout the vertical column with a mean delta value of −49.9 ± 0.45 ‰. The systematically more negative delta values occurred only as long as the nocturnal temperature inversion was present. During the September study, water samples were analysed as well for methane concentration and isotopic composition in order to provide a link between surface and atmosphere. The water samples reveal high variability on horizontal scales of a few tens of metres for this particular case. The airborne sampling system and consecutive analysis chain were shown to provide reliable and reproducible results for two samples obtained simultaneously. The method presents a powerful tool for distinguishing the source process of methane at different altitudes. The isotopic composition showed clearly depleted delta values directly above a biological methane source when vertical mixing was hampered by a temperature inversion, and different delta values above, where the air masses originate from a different footprint area. The vertical distribution of methane isotopic composition can serve as tracer for mixing processes of methane within the atmospheric boundary layer.

Die präzise Messung der Luftbewegung in der Atmosphäre ist essentiell für die meteorologische Grundlagenforschung. Die fluggestützte in-situ Windvektormessung ist hierfür ein wichtiges Werkzeug. Sie basiert auf der Messung des Anströmvektors des Flugzeugs, des Geschwindigkeitsvektors gegenüber der Erde und der Lagewinkel zur Transformation in ein gemeinsames Koordinatensystem zur Vektordifferenzbildung. Eigenschaften des Trägersystems gehen allenfalls als Störgrößen in die Messung ein. Segelflugzeuge weisen aufgrund ihrer aerodynamischen Güte eine hohe Sensitivität gegenüber der Vertikalwindkomponente auf. Die Nutzung dieser Eigenschaft zur in-situ Vertikalwindbestimmung ist in einigen Quellen beschrieben. Allen gesichteten Lösungen ist gemein, dass niederfrequente Flugbahnschwingungen dem ermittelten Vertikalwind überlagert sind. In der vorliegenden Arbeit wird die in-situ Messung des Windvektors unter Nutzung der Flugleistung eines Segelflugzeuges signifikant weiterentwickelt. Mittels analytischer und statistischer Modelle für die Beschreibung der Atmosphäre wird der Einfluss der bewegten Atmosphäre auf die Flugleistung abgeschätzt. Subjektive Bewertungen der herrschenden Turbulenz dienen zusammen mit Turbulenzkriterien aus der Meteorologie und der Luftfahrt, angewandt auf die Flugmessdaten, der Quantifizierung der erfahrungsgemäß zulässigen Turbulenzintensität. Das Flugleistungsmodell des verwendeten Segelflugzeugs wird um den Widerstandseinfluss der Reynoldszahl, des Schiebewinkels und der Drehbeschleunigung um die Querachse erweitert. Es ist Bestandteil der aus dem Impulsänderungssatz hergeleiteten und vereinfachten Bewegungs-gleichungen. Mit Hilfe der Flugleistung des Segelflugzeugs in den Bewegungsgleichungen wird ein Transformationswinkel bestimmt, der eine alternative Transformationsfolge zwischen den Koordinatensystemen im Vergleich zur direkten in-situ Windmessung ermöglicht. Anhand von Flugmessdaten und dem Vergleich mit bodengestützten Wind-LiDAR-Messungen wird die Plausibilität des aufgestellten Flugleistungsmodells, der Bewegungsgleichung und der angewandten Transformationsfolge gezeigt. Eine konservative Abschätzung der maximalen absoluten Unsicherheit zeigt relevant kleinere Unsicherheit der segelflugleistungsbasierten gegenüber der direkten in-situ Vektordifferenz-Windmessung., Measuring the wind vector in the atmosphere precisely is essential for meteorological research. Airborne in-situ wind vector measurement is an important and well known tool. It is based on measuring the airspeed vector of the aircraft, the velocity vector with respect to Earth and the aircraft attitude for transforming the velocity vectors into a common frame for vector subtraction. Characteristics of the carrier system are at most a disturbance in the measurement. Due to their aerodynamic quality, sailplanes have a high sensitivity to the vertical wind component. The use of this inherent characteristic for in-situ vertical wind determination is described in literature. Common to all these approaches is a correlation of low-frequency flight path oscillations and the determined vertical wind. In this thesis the in-situ measurement of the wind vector using the flight performance of a sailplane is substantially improved. By means of analytical and statistical models for the description of the atmosphere, the impact of the moving atmosphere on the sailplane flight performance is estimated. Subjective rating of the level of atmospheric turbulence is combined with meteorological and aviation turbulence criteria applied on inflight data to quantify the empirically acceptable turbulence intensity. The flight performance model is extended to the influence of Reynolds number variations, angle of side slip and angular accelerations at the cross axis. It is part of the equations of motion derived from the principle of linear and angular momentum. Simplifications are discussed with regard to the measuring task. Using the sailplane´s flight performance in the equations of motion, a transformation angle is determined, which allows an alternative sequence of transformation compared to the direct in-situ vector difference wind measurement. Based on inflight data and ground based wind-LiDAR measurements, the plausibility of the developed flight performance model and of the equations of motion is shown. The mostly unknown uncertainty characteristics of the flight state variables limit these considerations. A conservative estimation shows a relevant lower uncertainty for the sailplane performance based wind vector measurement compared with the direct in-situ vector difference wind measurement., Forschungsbericht Niedersächsisches Forschungszentrum für Luftfahrt, vol. 2018-04

The unmanned research aircraft ALADINA (Application of Light-weight Aircraft for Detecting in situ Aerosols) has been established as an important tool for boundary layer research. For simplified integration of additional sensor payload, a flexible and reliable data acquisition system was developed at the Institute of Flight Guidance, Technische Universität (TU) Braunschweig. The instrumentation consists of sensors for temperature, humidity, three-dimensional wind vector, position, black carbon, irradiance and atmospheric particles in the diameter range of ultra-fine particles up to the accumulation mode. The modular concept allows for straightforward integration and exchange of sensors. So far, more than 200 measurement flights have been performed with the robustly-engineered system ALADINA at different locations. The obtained datasets are unique in the field of atmospheric boundary layer research. In this study, a new data processing method for deriving parameters with fast resolution and to provide reliable accuracies is presented. Based on tests in the field and in the laboratory, the limitations and verifiability of integrated sensors are discussed.