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 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 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 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 Dealing with challenges of altimetry-based surface water height derivation over boreal catchments : case study of Mackenzie river(2022) Liu, JiaxinThe 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.Item Open Access Digitalisierung und Bereitstellung von historischen Luftbildern des Landesamts für Geoinformation und Landentwicklung Baden-Württemberg (LGL)(2017) Wein, IsabelDie Digitalisierung und Bereitstellung von historischen Luftbildern des Landesamts für Geoin-formation und Landentwicklung Baden-Württemberg (LGL) soll im Hinblick auf die dauerhafte Sicherung der wertvollen Luftbilder und die bessere Verfügbarkeit für die unterschiedlichen Kundengruppen vorangetrieben werden. Hierzu ist ein Konzept zu entwickeln. Im Rahmen des Digitalisierungsprozesses werden neben dem eigentlichen Scannen und Georeferenzieren in einer Vorbereitungsphase die Originalbilder aufbereitet. In einer Nachbereitungsphase werden Qualitätssicherungsmaßnahmen geprüft. Schließlich wird der Umfang des Digitalisierungsprojektes hinsichtlich Personal-, Sach- und Zeitaufwand eingeschätzt. Neben der nachhaltigen Sicherung dieser Luftbilder durch Digitalisierung soll durch eine standardisierte Bereitstellung der digitalen Luftbilder über das Internet, z. B. Geodatendienste, dem wachsenden Bedarf der Nutzer Rechnung getragen werden. Hierfür werden Speicherbedarf, Metadaten und Nutzungsrechte untersucht. Die vorhandenen Luftbildinformationssysteme in den Bundesländern Thüringen, Bayern, Hessen, Rheinland-Pfalz und Niedersachsen sowie in den Nachbarländern Schweiz und Österreich werden verglichen. Auffällig dabei ist der unterschiedliche Stand der Digitalisierung.Item Open Access Understanding the positive trend in total water storage of Ob river basin using spaceborne observation(2020) Yu, ZiqingIn recent years, a positive trend of total water storage is detected in many big basins. One of them is Ob river basin in west Siberia, where 27 million people live in 39 cities. In this thesis, measurements from GRACE and GRACE-FO mission are employed and analyzed to determine the total water storage change in this region since 2003. Meanwhile, precipitation and evapotranspiration from global datasets and runoff determined using satellite altimetry will also be taken into discussion to analyze the reasons of the trend. The data from different resources are summarized using Gauss-Markov adjustment. It was found that from the launch of GRACE till 2013 the total water storage has slightly decreased, from 2013 to 2015 this catchment has gained water due to increased precipitation and low evapotranspiration. After 2016, total water storage in this area has reduced because the precipitation is lower and the evapotranspiration is stronger.Item Open Access Comparison between gravity gradients from dense CryoSat-2 altimetry and from shipborne gradiometry(2017) Buss, RomanSatellite altimetry is a tool to gather information about Earth’s oceans and ice coverage on a global extent. Altimetric data can be used to monitor ice sheet changes, create bathymetric maps or analyze the sea surface. Extensive comprehension of the vast masses of water on Earth will benefit not only geodetic but also various scientific aspects. This paper will deal with altimetric data collected by ESA’s satellite CryoSat-2. The satellite is designed to perform measurements of both ocean surface and ice sheets. Vertical gravity gradients will be calculated on the basis of sea surface height measurement. The area of interest is located between Faroe Islands and Shetland Islands north of Scotland. The created vertical gravity gradients will be compared with a dataset collected by Bell Geospace via shipborne gradiometry. Satellite altimetry enables a rather convenient acquisition of global data compared to traditional gradiometric methods. The main objective is to find out whether satellite altimetry is a viable alternative to generate gravity gradient data on a global extent.