06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7

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Publication Type: search.filters.UBSTyp.Abschlussarbeit (Bachelor)Subject: search.filters.subject.620

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    Water level monitoring at SAPOS stations through GNSS-IR : a case study at the station Iffezheim
    (2023) Wagner, Sven B.
    The German SAPOS-Network comprises approximately 270 permanent GNSS receivers, capturing signals from Global Navigation Satellite Systems such as GPS, GLONASS, Galileo, and BeiDou. Primarily employed for generating kinematic, mathematical, and physical models within their respective regions, these receivers hold untapped potential for alternative applications. GNSS receivers capture multipath errors, typically considered unwanted interferences resulting from signal reflections off surfaces beneath the antenna. Despite their potential to adversely affect data precision, these interferences contain valuable information about the reflecting surface. As satellites pass through the receivers’ field of view at specific elevation angles, the interference between the direct and reflected signals leads to constructive and destructive patterns. This phenomenon occurs due to variations in signal phase between the direct and reflected signal, enhancing or dampening the signal strength. These variations in signal strength are captured in the satellites Signal-to-Noise Ratio (SNR) data. Spectral analysis of the SNR data can be used to determine the frequency of the interference pattern. Combining this frequency with the corresponding signal wavelength and satellite elevation angles allows the calculation of the vertical distance between the antenna phase centre and the reflecting surface on Earth. This method, known as GNSS Interferometric Reflectometry (GNSS-IR), provides a valuable means of monitoring surface information, including soil moisture, snow depth, and water levels. At SAPOS stations near rivers and water bodies, GNSS-IR offers a cost-effective, accessible, and innovative opportunity to gather water level information using the already existing infrastructure. This research explores the potential of GNSSIR for water level monitoring at SAPOS stations focusing on the Iffezheim station along the Rhine River near the City of Karlsruhe in southern Germany.
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    Analysis of coordinate transformation with different polynomial models
    (2017) Gao, Yueqing
    The main task of geodesy is providing geodetic networks with fixed points in order to create a uniform geographical spatial reference frame as a fundament for the data collection by the official geodesy survey institutes. A german geodesy survey institute called AdV (Arbeitsgemeinschaft der Vermessungsverwaltungen der Länder der Bundesrepublik Deutschland) declared in 1991 that the ETRS89 datum should be introduced in Germany as a reference system. In order to transform the already exciting coordinate informations in the Gauß-Krüger coordinate system into the later introduced UTM coordinate system, different transformation models have been developed and discussed. Besides the most commonly used 7-parameter Helmert transformation and 6-parameter affine transformation models, polynomial transformation models can also be applied. A method for improving the transformation results of a polynomial model will be discussed, with which a significance test (T-test) for each parameter will be done and the polynomial terms with lower significance to the model will be eliminated in order to get the optimal polynomial model. Here different transformation models are reviewed and the transformation results based on these models with the Least Squares estimation method are compared and analysed.
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    Analyzing the spatio-temporal behavior of Poyang Lake using Google Earth Engine
    (2020) Schneider, Nicholas M.
    Poyang Lake, China’s largest freshwater lake, undergoes a yearly repeating cycle of drastic inundation and subsequent considerable shrinkage. Essentially, as a result of local precipitation and feedings from its tributaries, as well as a natural water exchange with the Yangtze River, Poyang Lake experiences such dimensional fluctuations on a annual and interannual scale. The ongoing change plays a significant role for the surrounding anthropogenic activity and wildlife. Despite being considered as a hydrological phenomenon, the dynamics of this Chinese water body set up a hurdle for any accurate documentation of its regime and therefore remains insufficiently studied upon to this day. Further impeding the comprehension of Poyang Lake’s behavior is the near inaccessibility and nonexistence of in situ data, such as water level measurements and bathymetric maps. Consequently, this study, driven by its aim to analyze the spatio-temporal behavior of Poyang Lake, focuses solely on satellite observations. Making use of the cloud computing platform, Google Earth Engine, image time series are used from Landsat-8 and Sentinel-1 datasets in order to map Poyang Lake’s spatio-temporal behavior on an annual and interannual scale. Produced from the Landsat-8 dataset, results show that only under circumstances, do techniques, such as the combination of visible and infrared bandsand the calculation of the Normalized Difference Water Index, provide a reasonable approach for the delineation of continental water bodies. For the study on Poyang Lake, a water body subject to humid climate and thus frequent cloud coverage, these techniques do not apply very well. With synthetic aperture radar observations from the Sentinel-1 dataset, dynamic water masks, involving the removal of certain elevated areas and the classification of water from thresholding, could be generated. The resulting binary water masks are then merged with a digital terrain model to create monthly maps of the study area. The results show an evident correlation between this study’s visual and numeric findings. Although the results are nearly impossible to compare with any in situ data, they show a trend that annually occurs in Poyang Lake’s hydrological regime. In particular, they reveal the cycle of drastic inundation in rainy summer months and considerable shrinkage in dry winter months, especially when examining the years prior to 2019. Using SAR imagery for continental water body delineation, particularly in humid climates, proved to be a suitable technique and should be considered for future documentations of the lake.
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    Sea surface altimetry using GNSS-R
    (2018) Li, Fanxiang
    The Global Navigation Satellite Systems Reflectometry (GNSS-R) aims to retrieve information about the Earth surface by analyzing the signals emitted by GNSS transmitters (such as GPS, GLONASS, GALILEO and COMPASS...), and captured by an elevated platform after the signal has rebounded off of the oceans, lakes, land or ice and snow. The sea surface altimetry is an essential oceanic application of the GNSS-R. In this thesis, a method is introduced to solve this altimetric problem. Besides, a set of experimental data based on the campaign "Gold Test" carried out over the Mediterranean Sea in 2005 provided by the Institut de Ciències de l’Espai (ICE) is tested.
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    Analysis of helicopter-borne gravity gradiometry
    (2017) Xia, Zhuge
    Nowadays the FALCON partial tensor gravity gradiometer is the only applied AGG instrument to be used in a helicopter to collect high-resolution data for commercial demand. In order to know its principles and make full use of its advantages, in this study thesis, a helicopterborne gravity gradiometry data set offered by USGS is processed and analysed. It is interesting to figure out that whether the gradient tensor invariants are truly "invariant". Also through Fourier transformation, all gradient tensor components can be determined mathematically. Besides, the effects of terrain corrections and different flight line spacings and drape heights are also concerned to obtain high-resolution data in the easiest way.
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    Create a fluid-structure simulation framework for cycloidal rotors
    (2021) Schließus, Julian
    The deformation of cyclorotor blades caused by aerodynamic forces and its effect on the rotor efficiency is not well understood. Therefore the aim of this thesis is to set up coupled Fluid Structure Interaction (FSI) simulations of cycloidal rotors. Furthermore, the results of this work shall create a base for prospective refinements of current cyclorotor CFD models in using a coupled simulation. For the FSI setup, the Computational Fluid Dynamics (CFD) simulation software OpenFOAM and the Multibody Dynamics (MBD) simulation software MBDyn are coupled using the coupling library preCICE. During this thesis, MBDyn models are set up and the advantages and limits of the currently existing preCICE OpenFOAM- and MBDyn-Adapter are discussed. To extend the coupling possibilities into the territory of rotating bodies, the creation of a custom OpenFOAM class is explained in this work. In addition, the influence of the cell displacement tolerance on mesh deformation is investigated and issues in OpenFOAM such as unwanted scaling or nonphysical motions are solved. Further, 2D and 3D setup cases are run and tested successfully on a High Performance Computing (HPC) cluster. Finally, certain coupling methods are reviewed and evaluated for the considered case.
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    Spacecraft data simulator for the DESTINY⁺ Dust Analyser
    (2021) Kniese, Rafael
    This bachelor thesis reports on the development of a data simulator for the dust telescope "DESTINY⁺ Dust Analyser (DDA)". The DDA is part of DESTINY⁺, a space mission to the asteroid 3200 Phaethon, the presumed parent body of the Geminids. It will analyze cosmic dust released by the asteroid to better understand its role as a source of organic material on earth. The DDA will communicate with the rest of the satellite using the SpaceWire bus system and will be tested by the data simulator developed in this thesis, so that possible errors in the flight software can be detected and corrected as soon as possible. The need for this arises from the fact that the DDA is being realized at the Institute of Space Systems of the University of Stuttgart (IRS) together with the electronics supplier "von Hoerner & Sulger", while DESTINY⁺ is a mission of the Japan Aerospace Exploration Agency (JAXA). The German Aerospace Center (DLR) is the German project sponsor. The geographical distance between the experiment and the spacecraft is too large to perform direct tests in the early stages of the mission. The data simulator is implemented as two Graphical User Interfaces (GUIs) in C/ C++ in the Microsoft Visual Studio 2019 environment on Microsoft Windows 10. One sends data as broadcast or telecommand, the other receives telemetry. A SpaceWire Brick Mk3 from STAR-Dundee is used as the interface between the PC and the bus, which has two ports for SpaceWire cables and a USB port. Thus the data stream from and to the DDA can be controlled from a PC. The messages follow the packet protocol of the Consultative Committee for Space Data Systems (CCSDS). In the future, however, they will be adapted to the Remote Memory Access Protocol (RMAP).
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    Analyzing the surface height of Nam Co by using CryoTrack
    (2018) Liu, Mo
    In recent decades, the global climate change is increasingly accelerating and intensifying. The plateau climate is an important part of the global climate. In this thesis, we will take the plateau lake Nam Co as an object to research and analyze the climatic variation in this area. Since Nam Co is located in Tibet Plateau with a high elevation and it doesn’t have too much human disturbance, it is an ideal study object to observe. In this thesis, we will use the data from the satellite CryoSat-2 and the software CryoTrack to obtain the surface height of Nam Co as well as the trend of the water level variation of it. Meanwhile, by using CryoTrack we can also observe the frozen and breakup time of the lake ice.