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)Start date: 2020

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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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    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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    Estimation of significant wave height using Sentinel-3 data
    (2020) Gou, Junyang
    Coastal area is one of the most important area for us. More than 600 million people (around 10% of the word’s population) live in coastal areas that are less than 10m above sea level. Nearly 2.4 billion people (about 40% of the world’s population) live within 100km of the coast. Therefore, monitoring of coastal waters is extremely important. Due to the limitation of the number and location, the tide gauge stations around the world cannot provide a sufficient amount of in-situ data. Therefore, satellite altimetry plays an increasingly important role, especially when the SAR altimeter is put into use. However, due to the complexity of the coastal water surfaces, the performance of the satellite altimeter over the coastal area is far worse than over ocean. This thesis is dedicated to developing a method to determine one of the essential characters of the water surfaces - the significant wave height (SWH), using the Sentinel-3 data in the coastal area. The three primary steps of the method are extracting the thermal noise and the leading edge, fitting this part of waveform and determining the relationship between the new retracker and the physical model. In the first step, an algorithm is developed to avoid the interferences of the noise on the trailing edge. Therefore, the peak of the leading edge could be determined more accurately. The condition for the start point of the leading edge of the PLRM waveforms is Dwf > 0.01, inherited from ALES, whereas a more appropriate threshold for the SAR waveforms has been found as Dwf > 0.03. In the second step, the limitation of the Gauss-Markov model for the waveform adjustment has been discussed. Thus, the Levenberg-Marquardt method has been chosen to adjust the waveform. In the third step, the relationship between the raising time and the beta4 has been found. Then, we could estimate the SWH directly from the raising time which makes it possible to estimate the SWH from some complicated waveforms in coastal areas. We have employed the developed methodology to determine the significant wave height in the coastal area near the Cuxhaven. The quality of the results has been proved by comparing with the in-situ data from the Elbe measuring station provided by the Federal Maritime and Hydrographic Agency of Germany. The validation showed that the proposed method can determine reliable SWH from approximately 1km offshore, which is an improvement of earlier results.
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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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    Dealing with challenges of altimetry-based surface water height derivation over boreal catchments : case study of Mackenzie river
    (2022) Liu, Jiaxin
    The Earth is a watery place, which fills the oceans, rivers, and lakes. Approximately 71% of the Earth’s surface is water-covered. Measurements of surface water level in oceans, lakes, rivers and coastal waters are important for a variety of reasons. In the short term, this can, for example, help to alert to dangerous water level so that actions can be taken in advance, while in the long term, monitoring water levels can provide even greater insight into patterns of water dispersal in the area, and measure, for example, the effects of global warming. Satellite altimetry, which was originally designed for oceanography in the 1970s, has revolutionized our knowledge of the marine gravity field, of the dynamics of the oceans and even ofland hydrology. It is a space measurement technique that uses artificial satellites to measure the altitude from the satellite to the Earth’s surface. Due to its high resolution, global coverage and short revisit time, it is playing an increasingly important role in measurements of water level. For some years, this technology has also been used to retrieve water levels from rivers, lakes, and any inland water body as well. However, compared with the wide seas, measurements of inland water bodies involve many challenges. In this paper, we will take the Mackenzie River in northern Canada as a research object and process the data through the Matlab-based program Atlbundle+ to study the potential of inland altimetry, the problems it faces and the possible ways to find the solution. In general, there are two perspectives that will be considered: Firstly, how we can accurately remove outliers in the measurements, and secondly, how to improve the altimetry-driven water level time series by improving the retracking methods. Finally, based on the results and the procedure, a systematic analysis of the inland altimetry can be carried out.
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    Vorverarbeitung von Satellitenaltimetriedaten für die Analyse des zeitlich-variablen Schwerefelds
    (2020) Knogl, Robin
    Satellitenaltimetrie bietet die Möglichkeit großflächige, fortlaufende Zeitreihen von hochgenauen Messungen der Ozeantopographie zu erfassen. Daraus können wichtige Informationen zur ozeanischen Zirkulation abgeleitet und deren Einfluss auf das Erdklima besser verstanden werden. Sie können aber auch eine Alternative zur klassischen Schwerefeldmessung darstellen, indem man aus der Messung von Variationen der Ozeanoberfläche, Rückschlüsse auf Gravitationsanomalien zieht. Im Rahmen dieser Bachelorarbeit sollen Satellitenaltimetriedaten der Missionen Jason 1, Jason 2 und Envisat vorverarbeitet werden, um diese zur Analyse von Schwerefeldänderungen in Folge des Tohoku- Oki Erdbebens von 2011 nutzten zu können. Dazu wird das Datenformat der Ausgangsdaten zur leichteren Verarbeitung angepasst und die wichtigen Größen herausgefiltert. Zudem werden aus den gesamten Daten eines Jahres Zeitreihen der Sea Surface Height-Messungen, aus wiederholten Überflügen der Satelliten über den gleichen Bodenspuren, extrahiert. Aus den aufbereiteten Daten soll letztlich die Schwerefeldanomalie und ein Gravitationsgradient entlang der Bodenspuren der Satelliten berechnet werden.