06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access 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.Item Open Access Analysis of coordinate transformation with different polynomial models(2017) Gao, YueqingThe 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.Item Open Access 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.Item Open Access Sea surface altimetry using GNSS-R(2018) Li, FanxiangThe 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.Item Open Access Analysis of helicopter-borne gravity gradiometry(2017) Xia, ZhugeNowadays 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.Item Open Access Estimation of significant wave height using Sentinel-3 data(2020) Gou, JunyangCoastal 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.Item Open Access Noise characterization of GPS time series from the second IGS reprocessing campaign(2015) Wang, GanyiBy late 2013, the Analysis Centers (ACs) of the International Global Navigation Satellite System Service (IGS) begun the second reanalysis of the full history of Global Positioning System (GPS) data collected by the IGS global network since 1994 in a fully consistent way using the latest models and methodology. In this thesis, GPS time series of selected sites from different analysis centers were analysed with the software CATS. The purpose of this thesis is to discuss noise content using maximum likelihood estimation (MLE) and determine a noise model that can best describe the noise process in GPS time series of 20 years or more. The noise was assumed to be a combination of white noise and power-law noise. In the first part, we used fixed noise models with integer spectral indices for the MLE. The three noise models are: white noise only, white noise plus flicker noise (ƙ = -1) and white noise plus random walk noise (ƙ = -2). The estimated MLE values of different noise models were compared to determine the preferred noise model. Another noise parameter, amplitude, was also estimated. Latitude dependence of the noise amplitudes and the influence of data cleaning on the noise analysis were discussed. In the second part, the noise model was again assumed to be white noise plus power-law noise, but the spectral index of the power-law noise component was not fixed and was also estimated. The estimated spectral indices were compared with the results of the first part, in order to acquire a more precise description of the realistic noise components. At last, a comparison between the noise features of GPS time series from different ACs was made. Besides the results of noise analysis, the importance and practical value of noise analysis was also discussed.Item Open Access Analysis of river surface slope using ICESat-2 satellite altimetry(2022) Bao, JingyiItem Open Access Untersuchung von Schweredifferenzen durch Punktmassenmodellierung anhand der GRACE-Schwerefelddaten eines Gletschergebietes(2015) Hurt, PeterDie Eisschmelze und die damit einhergehenden Folgen für die Natur gehören zu den aktuellen Themen, die immer mehr in den Medien behandelt werden. Jährlich verlieren Gletschergebiete hunderte Gigatonnen an Eismasse und dieser Trend wird sich voraussichtlich auch in den kommenden Jahren fortsetzen. Das Abschmelzen von Gletschern trägt zudem maßgeblich zum Anstieg des Meeresspiegels bei. Das Augenmerk der meisten wissenschaftlichen Studien bezüglich der Gletscherschmelze liegt auf Grönland, da hier die größten Eismassenänderungen stattfinden. Dies liegt daran, dass sich auf Grönland nach der Antarktis die größten zusammenhängenden Eismassen befinden. In dieser Arbeit wird allerdings auf das bisher in diesem Zusammenhang eher weniger erforschte, von Gletschern überzogene Gebiet Alaskas eingegangen. Die Eismassenänderungen dieses Gebiets habe ich in dieser Arbeit mittels Punktmassenmodellierung untersucht. Die Massenschätzung der Punkte wird mit der Tikhonov-Regularisierung berechnet. Der Regularisierungsparameter wird dabei mittels L-Kurve bestimmt. Es konnte festgestellt werden, dass sich die mit dieser Methode geschätzten Eismassenänderungen der Alaskagletscher in einem realistischen Bereich bewegen.Item Open Access Create a fluid-structure simulation framework for cycloidal rotors(2021) Schließus, JulianThe 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.