06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

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

Browse

Filters

Settings

Start date: 2007Publication Type: search.filters.UBSTyp.Studienarbeit

Search Results

Now showing 1 - 10 of 21
  • Thumbnail Image
    ItemOpen Access
  • Thumbnail Image
    ItemOpen Access
    Noise performance of the modernized GPS and GALILEO systems
    (2010) Gerst, Sebastian
    With the modernization of GPS and the development of the new European satellite system Galileo, the noise performance of the newly introduced signals is understood insufficiently. Today, these new signals are not used operationally, but they are implemented in two satellites in the case of GPS and two Galileo test satellites. Both systems are emitting the new and conventional signals, which are recorded by a Septentrio receiver. The main goal of this thesis is to split the portion from the received signal, which is dependent on the temporal trend. On the one hand the satellite-receiver geometry, on the other hand the ionospherical runtime error. The resulting signal can be interpreted as noise, of which the correlation behavior and the power spectrum should be discussed.
  • Thumbnail Image
    ItemOpen Access
    GOCE data and gravity field model filter comparison
    (2008) Raizner, Carina
    New approaches with respect to space borne gravity observations are expected to significantly improve the overall knowledge of the Earth's gravity field and its geoid. The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is the first Core Earth Explorer Mission of the ESA Living Planet Programme. This new satellite mission based on the concept of satellite gradiometry is designed to support applications in Earth physics, oceanography and geodesy with an accurate and detailed global model of the Earth's gravity field and its geoid. One of the main problems in the use of the GOCE data is that the retrieval algorithms need along-track filtering on one hand and/or the implementation of spherical filters on the other. The match between these along-track one-dimensional filters and the spherical two-dimensional ones is far from obvious. Thus, the objective of this study is to investigate the influences of these two filter types by analyzing the differences between simulated GOCE reference and filtered data. Apart from closed-loop tests in order to check the consistency and correctness of the data and software used, the testing procedure for along-track as well as spherical filtering is implemented as follows. First, a global reference model is used for data generation which yields a reference signal along the orbit. By applying a one-dimensional along-track filter to these synthetic satellite data, a filtered global model is retrieved. On the other hand, the synthetic satellite data can be also generated after applying spherical filters to the global reference model. The outcome is a filtered global model estimated from these synthetic satellite data. The influences of both filter types are assessed by comparing the reference and filtered signals along the orbit as well as by comparing the reference and filtered models on the ground. Additionally, the properties of both filter types can be varied. In order to examine the empirical relation between along-track and spherical filters, transfer functions of the filters are investigated in a second step of this study. The transfer function for the spherical filter in the model domain is the ratio between reference and filtered signal which represents a corresponding one dimensional along-track filter in the signal domain. On the other hand, computing the ratio between reference and filtered model estimated from the along-track filtered signal relates the one-dimensional filter in the signal domain to a two-dimensional spherical filter in the model domain. The outcome of the study will be very useful for explaining some of the differences between current global model retrieval philosophies and will also be applicable to other satellite missions and data types in the future.
  • Thumbnail Image
    ItemOpen Access
    Literature analysis of SWOT mission from geodetic perspective
    (2012) Cao, Wenxi
    Satellite radar altimeter has been used for nearly twenty years to observe the variety of the global ocean surface topography. It has advanced our understanding of global ocean circulation and sea level change. However the conventional radar altimeter can not resolve the submesoscale features in the oceans because of its large spacing between satellite ground tracks and coarse ground resolution. On the other hand altimetry technique is expected to be able to observe large rivers, lakes and monitor the storage of freshwater on land. These new challenges require a new technique and a new mission. In 2016 a satellite mission called Surface Water and Ocean Topography (SWOT) will be launched by NASA and CNES according to plan. This term paper will summarize the general measurement principle, orbit design issues and applications of SWOT in the literature.
  • Thumbnail Image
    ItemOpen Access
    Analyse zweier Kameras für die UAS-Luftbilderfassung
    (2014) Leinss, Benedikt
    Die vorliegende Arbeit befasst sich mit zwei Kamerasystemen, welche in der photogrammetrischen Luftbilderfassung mithilfe von unbemannten Fluggeräten (sog. UAVs -- unmanned aerial vehicles) zum Einsatz kommen. Der Schwerpunkt liegt dabei auf einer vergleichenden Analyse der Bildqualität beider Kameras. Die Luftbilderfassung mit unbemannten Fluggeräten stellt eine kostengünstige Alternative zur bemannten Luftbildphotogrammetrie dar und gewinnt insbesondere bei der Erfassung kleinräumiger Gebiete zunehmend an Bedeutung. Das Landesamt für Geoinformation und Landentwicklung Baden-Württemberg führte daher 2012 in Zusammenarbeit mit dem Institut für Flugmechanik und Flugregelung (iFR) und dem Institut für Photogrammetrie (ifp) der Universität Stuttgart im Rahmen des Pilotprojekts "UAV@LGL" zwei Befliegungen an den Felsengärten bei Hessigheim mit zwei unterschiedlichen UAV-Trägersystemen und Kameras durch, wobei das Potential der Datenerfassung mittels UAS (unmanned aerial system) am praktischen Beispiel analysiert werden sollte. Die im ersten Flug eingesetzte digitale Kompaktkamera "Canon IXUS 100 IS" wurde im Rahmen dieser Arbeit zunächst unter anderem durch eine Hardware-Modifikation zur Vermeidung von Bewegungsunschärfen optimiert. Nach einer Markterhebung unter Berücksichtigung photogrammetrischer Anforderungen sollte ein alternatives Kamerasystem empfohlen werden. Diese digitale Systemkamera "Ricoh GXR Mount A12" wurde in Kombination mit einem Zeiss-Objektiv beim zweiten Flug eingesetzt. Zuvor galt es, die Kamera in das UAV-Trägersystem zu integrieren, sodass sich die Kamera über den Bordrechner des Fluggeräts auslösen lässt. In mehreren Testreihen wurde dabei auch die Auslöseverzögerung und Bildfolgezeit der Kamera ermittelt. Als Testmuster zur Analyse des geometrischen Auflösungsvermögens der Kameras dienten bei den Befliegungen am Boden ausgelegte Siemenssterne. Diese, aber auch weitere Bilddaten aus terrestrischen Untersuchungen mit Siemenssternen auf dem Campus der Universität Stuttgart, werden in einem MATLAB-Programm ausgewertet, welches bereits am ifp zur Verfügung stand, jedoch insbesondere zum Zweck der Analyse mehrerer Siemenssterne in einem Bild erweitert und um Ausgabegrafiken ergänzt wurde. Auch weitere Tests hinsichtlich der radiometrischen Bildqualität (chromatische Aberration, Vignettierung, Farbtreue, Bildrauschen, Dynamikumfang), welche teilweise im Testlabor der Firma "Image Engineering" in Köln/Frechen stattfanden, sind Gegenstand dieser Arbeit. Darüberhinaus wurden in photogrammetrischen Kamerakalibrierungen weitere Qualitätsaskpekte wie Punkt- und Längenmessgenauigkeit sowie die radialsymmetrische und tangentiale Verzeichnung evaluiert. Neben der detaillierten Gegenüberstellung der Ergebnisse dieser Untersuchungen erfolgt zur abschließenden Einschätzung der Bildqualität der beiden Kameras auch ein Vergleich zu professionellen Luftbildkameras, unter anderem zur digitalen Mittelformatkamera "DigiCAM" der Ingenieurgesellschaft für Interfaces mbH, welche hierzu ebenfalls einigen empirischen Untersuchungen unterzogen wurde. Die vorliegenden Resultate sprechen für eine insgesamt deutlich bessere Bildqualität des Ricoh/Zeiss-Kamerasystems gegenüber der Canon-Kompaktkamera. Bei einigen Bildqualitätsmerkmalen kann sich diese vergleichsweise günstige Systemkamera sogar mit der untersuchten professionellen "DigiCAM" messen.
  • Thumbnail Image
    ItemOpen Access
    Systematical analysis of the transformation procedures in Baden-Württemberg with least squares and total least squares methods
    (2007) Guo, Ronggang
    For the concrete "Introduction of ETRS89 into Baden-Württemberg" the transformation with the two models of the 7-Parameter Helmert transformation and the 6-Parameter Helmert transformation using the 131 collocated points (131 BWREF points in Baden-Württemberg) are firstly tested and discussed. Because of the special characteristic of the main triangle net of Baden-Württemberg (countrywide variable net scales, inhomogeneous point accuracies and transformation residual in the decimeter level) an alternative transformation procedure with the Total Least-Squares method is also applied in the estimation of the 7-Parameter Helmert transformation and 6-Parameter Affine transformation based on the 131 collocated points. After the review of basis mathematic background of the TLS method, these methods are complemented with MATLAB. Furthermore, 10 selected points are as test points to study the influence on those points after using TLS transformation parameters. The results are analyzed and compared with these results from the conventional LS method, and the advantages and shortcomings of this TLS method are discussed.
  • Thumbnail Image
    ItemOpen Access
    Concept study of a sailing offshore wind turbine
    (Stuttgart, 2021) Willeke, Leonard
    Wind turbines play an important role in the transition towards a sustainable future. With the demand for clean energy unbroken, suitable sites onshore become rare and more and more conflicts around land use arise. That’s why the industry moved to the sea, where wind resources and space are abundant. After the development of fixed-bottom and floating offshore wind turbines (FOWT), we now present the concept of a sailing offshore wind turbine (SOWT). It can enter deeper waters and will unlock more resources. The concept builds on the existing spar floating turbines. Specifically, the IEA Wind 15 MW reference turbine and the WindCrete spar are used. Simulations are run in OpenFASTv2.4, while the hydrodynamics of the spar are calculated in Ansys AQWA. The turbine is not attached to the sea floor but free to move. It is intended to sail with the wind like a ship. The turbine’s controller can be used to perform manoeuvres such as stop or turn. The turbine will produce power while sailing. It can store the energy onboard and will unload it periodically, e.g. to ships or stations. From this approach, many challenges arise. This work focuses on the stability. Special interest lies on the floater’s yaw stiffness which is very low. Due to the lack of mooring lines, it plays an important role for the stability. We concentrate on improving yaw stability by the instalment of underwater drag elements that slow down the yaw. Drag elements lead to a reasonable period of stability. Still, the turbine becomes unstable afterwards. Reason for this is the sideways force F_T,y, the y – component of the thrust force F_T. It is defined as F_T,y = F_T * sin{alpha_yaw}. The yaw angle alpha_yaw increases constantly under wind load, leading to an increase in F_T,y as well. Instabilities occur when F_T,y reaches a tipping point but not before. For steady wind with wind speeds v of 20 m/s and 25 m/s, the following pitch and roll are so strong that the rotor blades touch the water. For the lower wind speeds of 9 m/s and 17 m/s, pitch and roll are less strong. The turbine can recover and stabilize. The suggestion is to avoid the tipping point to prevent instabilities. Minimizing F_T,y can be achieved by the reduce of the thrust force F_T through rotor blade pitching. Another option is to control the yaw angle alpha_yaw through the nacelle yaw. Both strategies can be implemented into the turbine‘s controller.
  • Thumbnail Image
    ItemOpen Access
    Analysis of geodetic time series using allan variances
    (2010) Friederichs, Thomas
    The Allan variance is a statistical measure, developed in the 1960’s by the American physicist David W. Allan. With its aid, data series measured by devices like oscillators or gyroscopes can be analyzed with regard to their stability. In contrast to the Allan variance, the standard variance as a measure of total signal power, is not able to characterize signal stability. There exist further developments of the Allan variance. This student research project considers mainly non-overlapping, overlapping and modified Allan variances. The result of an Allan variance computation is the so-called sigma-tau-diagram. This diagram provides information about the stability and beyond, it allows identification of various random processes that exist in the series of measurement. The Allan variance may be computed directly in the time domain as well as via the frequency domain using the power spectral density of the time series and a transfer function. A domain conversion between the Allan variance and the power spectral density is only unidirectional. More precisely, one can compute the Allan variance by means of the power spectral density, but not vice versa. This student research project takes up the challenge of applying the concept of the Allan variance to geodetic time series (pole coordinates as part of the Earth orientation parameters, GPS measured coordinates of one position, Scintrex CG-5 gravimeter data and GOCE gravity gradients, in addition to oscillator frequencies). The Allan variance turns out to be a reasonable statistical measure for analysis of geodetic time series. The Allan variance, or better the Allan deviation, especially in an entire diagram, can be considered as a form of spectral analysis. Having said this, it is possible to consider the averaging interval tau as the inverted frequency.
  • Thumbnail Image
    ItemOpen Access
    Comparison of different ocean tide models especially with respect to the GRACE satellte mission
    (2012) Wu, Bohan
    For the modeling of a static gravity field, the impact of ocean tides is subtracted from the GRACE data. Since there are more than one ocean tide model available, it is worth to learn the difference between the models and the consequence of applying different model. Three ocean tide models FES2004, EOT08a and EOT10a provided in the form of tidal maps are compared in this thesis. Based on the tidal maps, the disturbance in the potential and in the acceleration due to a single ocean tide is derived by using spherical harmonic analysis. Tools for visualization are developed to demonstrate the difference between the EOT models and FES2004 globally at a specific time point or locally at a specific site in a time period. Furthermore, a simulation of the GRACE mission and spherical harmonic analysis using the differential gravimetry approach build a closed loop simulation together, from which it can be find out, how the model difference affects the gravity field derived from GRACE data in the frequency domain.
  • Thumbnail Image
    ItemOpen Access
    Photography-aided gravity modeling of solid bodies
    (2010) Lorenz, Christof
    Not all secrets of the The Great Pyramid of Giza were revealed, even after centuries of observation and research. One of the main questions concerns the construction of the pyramid. The most popular and reasonable theory assumes the old Egyptians to use an exterior ramp in the lower third and an interior ramp in the upper two thirds of the pyramid on which the stones were carried upstairs. However, there is no evidence that this is really true. Microgravimetry-measuring techniques are able to give information about the inner mass distribution of the pyramid and hence reveal yet unknown facts about the inner structure. Therefore, a reference gravity signal must be computed in order to detect mass deviations in the inside. In this work, an approach is discussed which uses photographs to construct a three-dimensional model of a body. It is shown that the information gained from three-dimensional reconstruction can be used to construct a solid body. For the computation of the gravity signal of this solid body an algorithm is applied which transforms the volume integral in Newton's law of gravity into line integrals, which allows the computation of gravitational quantities for arbitrary polyhedra. With the help of a small section of the Great Pyramid it is shown that detecting inner mass deviations from a reference body requires detailed knowledge about the surface. As the errors in the measured gravity signal caused by a mis-modeled body might have a high magnitude, the signal from inner mass deviations might completely vanish. However, if the surface of an object is well known it is indeed possible to make a statement about the inner structure of a body based on close-mesh measurements on its surface.