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 A MATLAB toolbox for the Scintrex CG-5 gravimeter at GIS(2017) Gu, SiyunThis thesis is about a MATLAB toolbox for the Scintrex CG-5 gravimeter. The aim of this toolbox is to offer a basic data process for gravity measurement, which is compatible for most applications in geodesy. In particular, the toolbox covers: 1. data selection, 2. adjustment, 3. gravity gradient computation, 4. gravity visualization, 5. calibration factor estimation. A graphical user interface enables users without deeper programming knowledge to operate this toolbox and obtain the results like adjusted values or figures.Item Open Access Materiell und lokal inkompressible viskoelastische Erdmodelle : Theorie und Anwendungen in der glazialen Isostasie(2004) Thoma, Malte; Wolf, Detlef (Prof. Dr. habil.)Die vorliegende Untersuchung beschäftigt sich mit glazial-isostatischen Ausgleichsvorgängen, wie sie in Island (rezentes Abschmelzen der Vatnajökull-Eiskappe) oder in Kanada und Fennoskandien (Abschmelzen der pleistozänen Eisschilde) beobachtet werden. Zur Berechnung des Ausgleichs wird ein mehrschichtiges sphärisches Erdmodell verwendet, dessen hydrostatischer Anfangszustand durch Auflasten gestört wird. Die viskoelastischen Materialeigenschaften des Erdinnern werden mit Hilfe der Maxwell-Rheologie simuliert. Weiterhin wird lokale Inkompressibilität vorausgesetzt, was eine konsistente Berücksichtigung der durch Selbstkompression bedingten Dichtezunahme mit der Tiefe gestattet. Nach Linearisierung und Laplace-Transformation der inkrementiellen Feldgleichungen ergibt sich für die Feldgrößen Verschiebung, Spannung und Gravitationsbeschleunigung ein gekoppeltes lineares Differentialgleichungssystem, das mit Hilfe der Kugelflächenfunktionsentwicklung analytisch gelöst wird. Nach einem numerischen Vergleich ebener und sphärischer Erdmodelle werden als Anwendung der Theorie die glazial-isostatischen Ausgleichsvorgänge in Island und Fennoskandien interpretiert. Für Fennoskandien ist es notwendig, neben der Eislast auch die gekoppelte Ozeanlast zu berücksichtigen. Hierzu werden verschiedene Näherungslösungen der "sea-level equation" präsentiert. Die wichtigsten Ergebnisse der Untersuchung lassen sich wie folgt zusammenfassen: * Bei der Interpretation glazial-isostatischer Beobachtungen führen ebene Erdmodelle nur zu befriedigenden Ergebnissen, wenn der Lastradius kleiner als 1500 km ist, das Erdmodell eine elastische Lithosphäre besitzt und die Beobachtungsorte in der Nähe des Lastzentrums liegen. Ist eine dieser Voraussetzungen nicht erfüllt, sollte ein sphärisches Erdmodell verwendet werden. * Die Interpretation des durch das Abschmelzen der Vatnajökull-Eiskappe hervorgerufenen rezenten Ausgleichsvorgangs (Landhebungsrate und Neigungsänderung) weist auf eine Lithosphärenmächtigkeit von 10 bis 20 km und eine Asthenosphärenviskosität von 5*10^16 bis 1*10^18 Pa s hin. * Der gravitative Einfluß des während einer Klimaerwärmung aus den vereisten Gebieten in die Ozeane abgeführten Schmelzwassers muß in die Interpretation des glazial-isostatischen Ausgleichs einbezogen werden. Die hiermit verbundene Lastumverteilung wird mit Hilfe der "sea-level equation" quantitativ beschrieben und numerisch bestimmt. * Zur Interpretation des Ausgleichsvorgangs in Fennoskandien werden die postglaziale Landhebung sowie die gegenwärtigen Raten der Landhebung, Neigungsänderung und Schwereänderung berücksichtigt. Die Modellierung ergibt Viskositäten des oberen und unteren Mantels von etwa 0.55*10^21 Pa s bzw. 1*10^21 Pa s, eine Lithosphärenmächtigkeit von 50 bis 80 km und eine maximale Eismächtigkeit von etwa 2000 m. Die Berücksichtung einer Asthenosphäre führt zu keiner nennenswert verbesserten Anpassung an die Beobachtungsdaten.Item Open Access Dynamic water masks from optical satellite imagery(München : Verlag der Bayerischen Akademie der Wissenschaften, 2019) Elmi, Omid; Sneeuw, Nico (Prof. Dr.-Ing.)Investigation of the global freshwater system has a vital role in critical issues e.g. sustainable development of water resources, acceleration of the hydrological cycle, variability of global sea level. Measurement of river streamflow is vital for such investigations as it gives a reliable estimate of freshwater fluxes over the continents. Despite such importance, the number of river discharge gauging station has been decreasing. At the same time, information on the global freshwater system has been increasing because of various types of ground observations, water-use information and spaceborne geodetic observations. Nevertheless, we cannot answer properly crucial questions about the amount of freshwater available on a certain river basin, or the spatial and temporal dynamics of freshwater variations and discharge, or the distribution of world’s freshwater resources in the future. The lack of comprehensive measurements of surface water storage and river discharge is a major impediment for a realistic understanding of the hydrological water cycle, which is a must for answering the aforementioned questions. This thesis aims to improve the methods for monitoring the surface extent of inland water bodies using satellite images. Satellite imaging systems capture the Earth surface in a wide variety of spectral and spatial resolution repeatedly. Therefore satellite imagery provides the opportunity to monitor the spatial change in shorelines, which can serve as a way to determine the water extent. Each band of a multispectral image reveals a unique characteristic of the Earth surface features like surface water extent. However selecting the spectral bands which provide the relevant information is a challenging task. In this thesis, we analyse the potential of multispectral transformations like Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA) to tackle this issue by condensing the information available in all spectral bands in just a few uncorrelated variables. Moreover, we investigate how the change between multispectral images at different epochs can be highlighted by using the transformations. This study proposes an automatic algorithm for extracting the lake water extent from MODIS images and generating dynamics lake masks. For improving the accuracy of the lake masks and computational efficiency of the algorithm, two masks are defined for limiting the search area. The restricting masks are developed according to DEM of the surrounding area together with a map of the long-term variation of pixel values. Subsequently, an unsupervised pixel-based classification algorithm is applied for defining the lake coastline. The algorithm particularly deals with the challenges of generating long time series of lake masks. We apply the algorithm on five lakes in Africa and Asia, each of which demonstrates a challenge for lake area monitoring. However in the validation section, we demonstrate that the algorithm can generate accurate dynamic lake masks. Rivers show diverse behaviour along their path due to the contribution of different parameters like gradient of the elevation, river slope, tributaries and river bed morphology. Therefore for generating accurate river reach mask, we need to consider additional sources of information apart from pixel intensity. The region-based classification algorithm that we propose in this study takes advantages of all types of available information including pixel intensity and spatial and temporal interactions. Markov Random Fields provide a flexible frame for interaction between different sources of data and constraint. To find the most probable configuration of the field, the Maximum A Posteriori solution for the MRF must be found. To this end, the problem is reshaped as an energy minimization. The energy function is minimized applying graph cuts as a powerful optimization technique. The uncertainty in the graph cuts solution is also measured by calculating the minimum marginal energies. The proposed method is applied to four rivers reaches with different hydrological characteristics. We validate the obtained river area time series by comparing with in situ river discharge and satellite altimetric water level time series. Moreover, in this study, we present river discharge estimation models using the generated river reach masks. Our aim is to find an empirical relationship between the average river reach width and river discharge. The statistics in the validation periods support the idea of using river width-discharge prediction models as a complementary technique to the other spaceborne geodetic river discharge prediction approaches.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 A regional analysis of GNSS-Levelling(2008) Raizner, CarinaDie herkömmliche Methode zur präzisen Höhenbestimmung ist das Nivellement. Durch die verbesserte Genauigkeit des Geoids, das von den neuesten und von CHAMP und GRACE (und in Zukunft GOCE) abgeleiteten Modellen des Gravitationspotentials bereitgestellt wird, kann das sogenannte „GNSS-levelling“ als eine Alternative für praktische Höhenanwendungen in Betracht gezogen werden. Der Schwerpunkt dieser Arbeit liegt in einer detaillierten Analyse einer optimalen Kombination von heterogenen Daten, die sich aus Ellipsoid-, orthometrischen und Geoidhöhen eines Höhenfestpunktnetzes zusammensetzen. Das Verhältnis zwischen diesen drei verschiedenartigen Höhen basiert theoretisch auf einer einfachen linearen Gleichung. Nachdem aber zahlreiche Faktoren, wie z.B. Datumsinkonsistenzen und systematische Fehler, zu Abweichungen zwischen diesen kombinierten Höhendaten führen, wird ein Modell als Korrekturfläche integriert. Die Eignung ausgewählter Modelle wird anhand verschiedener empirischer und statistischer Tests beurteilt. Um der Korrelation zwischen den Modellparametern entgegenzuwirken, wird das Gram-Schmidtsche Orthonormalisierungsverfahren angewandt und die Testergebnisse mit jenen von orthogonalen und nicht-orthogonalen Basisfunktionen verglichen. Zusätzlich wird eine Varianzkomponentenschätzung auf die kombinierte Ausgleichung der drei Höhen angewandt, um die Eignung des stochastischen Modells zu überprüfen, d.h. um zufällige Fehler zu separieren und die zugehörigen Varianz-komponenten für jeden Höhentyp zu schätzen. Außerdem wird eine detaillierte Studie über geeignete Methoden zur Überprüfung der Daten durchgeführt, um grobe Fehler zu entdecken und zu eliminieren. Schließlich beinhaltet diese Arbeit auch die Implementierung einer Interpolation mit radialen Basisfunktionen. Diese stellen eine orthonormale Basis dar, mit der eine Oberfläche mit unabhängigen Parametern bestimmt werden kann. Gleichzeitig hängt die entsprechende Effizienz der Fläche nicht vom Entwicklungsgrad der Basisfunktionen ab. Die Optimierung des in dem Interpolationskern enthaltenen Formparameters wird mittels eines genetischen Algorithmus (GA) realisiert, um den Interpolationsfehler zu minimieren. Diese Methode bietet den Vorteil, dass sie differenzierbar ist und somit kann die Verteilung der Daten berücksichtigt werden. Mögliche Oszillationen in der Parameterfläche können vermieden werden. Die Wirkungsweise dieser inversen multiquadratischen Funktion wird durch eine spezielle Kreuzvalidierung beurteilt, welche eine höhere Effizienz aufweist als das klassische Verfahren. Die beschriebenen Ansätze werden anhand des aktuellen Geoidmodells und anhand von GPS und Nivellierdaten in Kanada und einzelnen Teilregionen evaluiert.Item Open Access Monitoring inland surface water level from Sentinel-3 data(2019) Wang, BoInland surface water bodies (e.g. lakes and rivers) are very important to the nature and human society. To monitor the water level of inland water bodies, gauge stations were built since 19th century, but the amount of the stations is declining since the 1970s because of lack of maintenance. An accurate and continuous monitoring of lakes and rivers is available because of the satellite altimetry missions launched, e.g. Jason-2 and ENVISAT. These satellites can provide water level with proper spatial and temporal resolution. In the recent past, researchers have used different satellite mission observations to generate time series of inland water level in order for monitoring the water bodies. In this thesis, we use the new designed satellite mission Sentinel-3, which carries different sensors, to generate the water level time series of Dongting Lake and Poyang Lake in China. Initially, we combine the altimetry measurements with satellite images to determine virtual station. We choose Sentinel-3 Ku band data and on-board Ocean tracker to generate the water level time series. Afterwards, we apply different waveform retracking algorithms (5β-parameter and OCOG) to compare the results with on-board tracker. We also validate the results with the other database, then investigate the waveforms of each sampling date. The comparisons show the three tracking methods we used are capable to Quasi-Specular waveforms, and OCOG shows the best result to flat patch waveforms. Furthermore, some suggestions for improvements are also discussed in the last chapter.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 Characterizing storage-based drought using satellite gravimetry(2021) Saemian, PeymanDrought is a complex phenomenon leading to a wide range of socio-economic, environmental, and political problems. The storage-based drought which represents the persistent lack of water in different levels of the Total Water Storage (TWS) from deep groundwater to surface water plays a vital role in proactive drought management. Despite its necessity, TWS could not be monitored due to the lack of consistent measurements from regional to continental scale. Since its launch in 2002, the Gravity Recovery and Climate Experiment (grace) mission and its successor GRACE Follow-On have provided unique observations of the TWS change at the global scale. In this study, we have investigated characterizing the storage-based drought at the global scale using GRACE measurements. To this end, the Equivalent Water Height (EWH) has been retrieved from GRACE level 02 solutions. We have addressed the short record of GRACE observations in capturing the full hydroclimate variations. Based on our analysis, regions with a considerable direct human intervention like overexploitation of groundwater in the Middle East, regions that were affected by climate change like ice-melting over the Mackenzie river basin in Canada, or extreme precipitation events over the Ob river basin in the boreal regions are more sensitive to the length of ewh time series. Due to the crucial need for a long (at least 30 years) record of EWH, we have extended GRACE observations back to 1980 using an ensemble of models. The extended dataset has been developed using a pixel-wise selection of best-performed models among global hydrological models, land surface models, and atmospheric reanalysis models. The extended dataset has been used in the study for drought characterization over the grac period. The proposed Storage-based Drought Index (SDI) successfully captured the documented drought events globally in terms of intensity and spatio-temporal distribution. Moreover, the analysis of SDI over the five classes of drought from D0 as abnormally dry to D4 as exceptional drought showed that most regions have suffered at least once from the storage-based drought over the GRACE period (2002–2016). Besides, the map of exceptional drought frequency highlights regions with significant groundwater extraction like California, the Middle East, and north of India and regions with exceptional shifts in the precipitation and temperature pattern and intensity like Amazon in South America and China. Finally, our comparison of SDI with three most widely used drought indices namely the Standardized Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration Index (SPEI), and the Palmer Drought Severity Index (PDSI) reveals that despite their high correlation over climate-driven regions, these indices failed to characterize anthropogenic drought events, especially over regions with considerable groundwater withdraws. The study allows for a more informative storage-based drought with a more robust climatology as the reference, thus enabling a more realistic risk assessment.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.