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Analysing normal modes of the Earth from high-rate GNSS time series / Zhongyi Chen (2017)  

Public Titre : Analysing normal modes of the Earth from high-rate GNSS time series Type de document : Mémoire Auteurs : Zhongyi Chen, Auteur Editeur : Stuttgart : University of Stuttgart Année de publication : 2017 Importance : 78 p. Format : 21 x 30 cm Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] déformation de la croute terrestre [Termes IGN] oscillation [Termes IGN] positionnement différentiel [Termes IGN] positionnement ponctuel précis [Termes IGN] rapport signal sur bruit [Termes IGN] séisme [Termes IGN] série temporelle Résumé : (auteur) Normal modes of the Earth, or Earth’s free oscillations, correspond to a global deformation of the Earth that vibrates at different frequencies, like a bell, after a strong excitation, usually an earthquake of magnitude greater than 6.5. Normal modes of the Earth were first described by Lord Kelvin (Kelvin, 1863) with a computation of the lowest fundamental spheroidal mode 0S2 frequency for a homogeneous Earth model (Lognonné and Clévédé, 2002). With the theory and the deployment of the first long-period sensors in the late 1950s, day-scale Earth’s free oscillation after large earthquakes has been detected by underground instruments such as strainmeters, gravimeters and seismometers (Benioff et al., 1961) (Dziewonski and Gilbert, 1972) (Mendiguren, 1973). In the 1960s, since the U.S. military developed the first satellite navigation system, Transit, the era of Global Navigation Satellite System (GNSS) has arrived. Among all navigation satellite systems, Global Positioning System (GPS), operated by the U.S. Department of Defense (DOD), is currently the world’s most utilized satellite navigation system. With the developments of receiver technology and sampling capability, GPS becomes a powerful tool to study long-period Earth deformations such as plate tectonics and post-glacial rebound, or to monitoring short-period and short-duration motion such as waves generated by earthquakes (Bilich et al., 2008). In recent years, several studies have demonstrated the effective use of GPS in estimating coseismic displacement waveforms induced by an earthquake with accuracies ranging from a few millimeters to a few centimeters. In these studies, two well-known processing strategies, single Precise Point Positioning (PPP) and Different Positioning (DP), have been used to reduce the latency between earthquake occurrence and coseimic displacement waveforms estimation. In this thesis, a new approach named Variometric Approach for Displacements Analysis Standalone Engine (VADASE) is used to detect the normal modes of the Earth. Then the Welch’s PSD estimate is applied to transform the time series into frequency domain. Several simulations have been performed on synthetic time series to investigate the influence of noise level, sampling rate, time series length, window size and overlapping rate of Welch’s method, as well as the influence of stacking. The experiments on real data show the capability of VADASE time series for detecting normal modes of the Earth with the help of the stacking method. Some fundamental modes with small amplitude are not visible because the SNR is not sufficient to lift the signal out of the noise. Note de contenu : 1- Normal modes of the Earth 2- GPS system 3- GPS positioning 4- GPS data processing 5- Spectral analysis 6- Simulations 7- Experiments on real Vadase time series Numéro de notice : 17576 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Mémoire masters divers DOI : 10.18419/opus-9317 En ligne : http://dx.doi.org/10.18419/opus-9317 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92281

Instantaneous estimation of attitude from GNSS / Hendy Fitrian Suhandri (2017)  

Public Titre : Instantaneous estimation of attitude from GNSS Type de document : Thèse/HDR Auteurs : Hendy Fitrian Suhandri, Auteur ; Alfred Kleusberg, Directeur de thèse ; Hasanuddin Zainal Abidin, Directeur de thèse Editeur : Stuttgart : University of Stuttgart Année de publication : 2017 Importance : 143 p. Format : 21 x 30 cm Note générale : Bibliographie thesis accepted by the Faculty of Aerospace Engineering and Geodesy of the University of Stuttgart in partial fulfilment of the requirements for the degree of Doctor of Engineering Sciences (Dr.-Ing.) Langues : Anglais (eng) Descripteur : [Termes IGN] ambiguïté entière [Termes IGN] angle d'Euler [Termes IGN] double différence [Termes IGN] filtre de Kalman [Termes IGN] méthode des moindres carrés [Termes IGN] modèle stochastique [Termes IGN] orientation de véhicule [Termes IGN] positionnement cinématique [Termes IGN] positionnement par GNSS [Termes IGN] récepteur GNSS [Termes IGN] simple différence [Vedettes matières IGN] Traitement de données GNSS Résumé : (auteur) The use of the Global Navigation Satellite System (GNSS) is widely spread from position determination to attitude determination of a platform in space. This system offers time invariant estimation position. Another thing that can be an advantage is that the flexibility to operate the GNSS receiver variants, from the low-cost until the high-performance GNSS receivers. In terms of attitude determination application at least three receivers are required to determine three spatial axes, where the cost-effective GNSS attitude determination systems can be constructed with today’s receiver technology. At the moment, however, algorithms are lacking which are fast and efficient enough to estimate the position angles without delay. For this reason, the present work deals with the development of algorithms for the attitude determination in space of a platform under the help of the "GNSS" Global Positioning System (GPS). The investigation through this work is classified into three sequential parts: The first part is the estimation of the optimal configuration of baseline array as well as the estimation of the integer ambiguity of carrier phase differences. The estimated integer ambiguity is then used to estimate the high precision baseline coordinates. The second part is to estimate the attitude of the platform in space by means of quaternion using batch process, and the last part is to improve the algorithm using a recursive algorithm for the kinematic application purpose. The precise attitude determination about three spatial axes is possible if at least three GNSS receivers with fixed baselines are used in particular array configurations. Assuming that the basic lengths of the baselines are known a priori, the attitude angles can be calculated via the combination of carrier phase and pseudorange observations. Since the carrier of the GPS signal is propagated in short-wave form, the measured phase differences are ambiguous. The multiples of the GPS signal phases together with the baseline lengths are therefore estimated and improved in a first step with the aid of the a priori baseline lengths information. The multiple-baseline float solution estimation method is used. However, the approach does not provide optimal results. Therefore, an alternative algorithm for the float solution is presented, which estimates the float solution by using the socalled the gradient based iterative method of the least-squares. It shows that method is able to give convergent estimate parameter. It is also shown here that the proposed method outperforms the conventional iterative least-squares in terms of iteration number and computational time. For instantaneous applications, the Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) method is not optimal for fixing the integer multiples of the carrier phase differences for several baseline lengths. In addition, this method requires a high computational effort as soon as a larger number of baseline lines enter into the calculation. An improvement in this work is utilising the partial LAMBDA method, which only uses a subset of the integer multiples to be determined. This algorithm improves the determination of integer multiples and precise calculation of the baseline lengths. The advantages of this algorithm are discussed, and it is empirically demonstrated that the ambiguities are better resolved. Furthermore, the estimation of the attitude angles with the aid of quaternions is theoretically improved and analysed. Two processing strategies are investigated: the least-squares method and the Kalman Filter (KF) method. For the static case, the least-squares is applied and tested. Simulations show that the developed gradient based iterative method of the least-squares provides better estimates than the conventional adjustment methods. It is also shown that the number of iterations required is less and the computational time is reduced. This algorithm is not useful for kinematic applications where a fast sequence of results is required. A modified Extended Kalman Filter (EKF)-Like algorithm is used for kinematic applications. Experiments show that with this algorithm more stable quaternions can be calculated with fewer outliers than when they are determined by the least-squares method. All newly developed algorithms are theoretically analysed and subjected to extensive simulations and experimental kinematic tests in the field. Note de contenu : Introduction 1 - General mathematical model of GNSS positioning 2 - Multi-baseline GNSS estimation method 3 - GNSS based attitude determination 4 - Recursive attitude determination 5 - Experimental result of static and kinematic tests 6 - Summary, conclusion and future work suggestion Numéro de notice : 21574 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : Doctor thesis : Engineering sciences : Stuttgart : 2017 DOI : 10.18419/opus-9239 En ligne : http://dx.doi.org/10.18419/opus-9239 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90576

Visual analytics of human mobility behavior / Robert Lutz Krüger (2017)  

Public Titre : Visual analytics of human mobility behavior Type de document : Thèse/HDR Auteurs : Robert Lutz Krüger, Auteur ; Thomas Ertl, Directeur de thèse ; Ross Maciejewski, Directeur de thèse Editeur : Stuttgart : University of Stuttgart Année de publication : 2017 Importance : 212 p. Format : 21 x 30 cm Note générale : Bibliographie Von der Fakultät Informatik, Elektrotechnik und Informationstechnik der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.), genehmigte Abhandlung Langues : Anglais (eng) Descripteur : [Termes IGN] acquisition de données [Termes IGN] analyse visuelle [Termes IGN] base de données localisées [Termes IGN] comportement [Termes IGN] données de terrain [Termes IGN] données socio-économiques [Termes IGN] enrichissement sémantique [Termes IGN] exploration de données géographiques [Termes IGN] mobilité humaine [Termes IGN] modélisation [Termes IGN] trajet (mobilité) [Vedettes matières IGN] Géovisualisation Résumé : (auteur) Human mobility plays an important role in many domains of today’s society, such as security, logistics, transportation, urban planning, and geo-marketing. Both, government and industry thus have great interest in understanding mobility patterns and their driving social, economical, and environmental causes and effects. While stakeholders had to rely on manual traffic surveys for a long time, improvements in tracking technology made analyses based on large digital datasets possible. Recently, the omnipresence of mobile devices significantly increased the amounts of collected movement and context data. People are willing to reveal their position, but also further personal details such as visited places, observations, events, news, and sentiments in exchange for personalized services and social networking. This opens up new possibilities for many domains where a semantic mobility understanding is required but also raises major challenges. To reveal a holistic picture, heterogeneous datasets of different services with different resolution and format have to be fused and analyzed. However, social sensing data is vast, has varying scale, is unevenly distributed, and constantly updated. Especially content from social media services is often inconsistent, unreliable, and incomplete, which requires special treatment. Fully automatic mapping approaches are not trustworthy as they do not take into account these uncertainties. At the same time, manual approaches become insufficient with large amounts of data. Even when data is perfectly aligned, analysts cannot purely rely on existing techniques. Answering questions about reasons for movement requires a broader perspective that takes into account environmental and social context, the driving forces for human mobility behavior. Visual analytics is an emerging research field to tackle such challenges. It creates added value by combining the processing power and accuracy of machines with human capabilities to perceive information visually. Automatic means are used to fuse and aggregate data and to detect hidden patterns therein. Interactive visualizations allow to explore and query the data and to steer the automatic processes with domain knowledge. This increases trust in data, models, and results, which is especially important when critical decisions need to be made. The strengths of visual analytics have been shown to be particularly advantageous when problems and goals are underspecified and exploratory means are needed to discover yet unknown patterns. This thesis presents novel visual analytics approaches to derive meaning and reasons behind movement, by taking into account the aforementioned characteristics. The approaches are aligned in a holistic process model covering all steps from data retrieval, enrichment, exploration, and verification to externalization of gained knowledge for various fields of application such as electric mobility, event management, and law enforcement. It is shown how data from social media can not only be used to retrieve up-to-date movement information, but also to enrich movement trajectories from other sources with structured and unstructured information about places, events, transactions, and other observations. Through highly interactive visual interfaces analysts can bring in domain knowledge to deal with uncertainties during data fusion and to steer the subsequent semantic analysis. Exploratory and confirmatory analysis techniques are presented to create hypotheses, refine them, and find support in the data. Analysts can discover routines and abnormal behavior with assistance of automatic pattern detection methods to cope with the vast amounts of data. Spatial drill-down is supported by a set-based focus+context technique, while a more abstract visual query language allows to explicitly formulate, extract, and query for movement patterns. The approaches are applied in different scenarios and are integrated in a visual analytics system. Evaluation with experts and novice users, case studies, and comparisons to ground truth data reveal the need and effectiveness of the contributions. Overall, the thesis contributes a visual analytics process for human mobility behavior with novel semantic analysis approaches, ranging from global movements of many to local activities of a few people, for a wide range of application domains. Note de contenu : Introduction 1 - From Foundations to Applications 2 - Movement Data Retrieval and Visual Representation 3 - Semantic Enrichment with Context Data 4 - Interactive Filtering 5 - Pattern Detection and Verification 6 - MOBY - The Mobility Analysis System Conclusion and Outlook Numéro de notice : 21573 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Thèse étrangère Note de thèse : PhD Dissertation : Informatik, Elektrotechnik und Informationstechnik : Universität Stuttgart : 2017 DOI : sans En ligne : http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-ds-97337 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90574

Visualization of two-phase flow dynamics: Techniques for droplet interactions, interfaces, and material transport / Grzegorz Karol Karch (2017)  

Public Titre : Visualization of two-phase flow dynamics: Techniques for droplet interactions, interfaces, and material transport Type de document : Thèse/HDR Auteurs : Grzegorz Karol Karch, Auteur ; Thomas Ertl, Directeur de thèse ; H. Theisel, Directeur de thèse Editeur : Stuttgart : University of Stuttgart Année de publication : 2017 Importance : 180 p. Format : 21 x 30 cm Note générale : Bibliography Von der Fakultät Informatik, Elektrotechnik und Informationstechnik und dem Stuttgart Research Centre for Simulation Technology der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.), genehmigte Abhandlung Langues : Anglais (eng) Descripteur : [Termes IGN] analyse visuelle [Termes IGN] mécanique des fluides [Termes IGN] visualisation 4D Index. décimale : THESE Thèses et HDR Résumé : (auteur) Computational visualization allows scientists and engineers to better understand simulation data and gain insights into the studied natural processes. Particularly in the field of computational fluid dynamics, interactive visual presentation is essential in the investigation of physical phenomena related to gases and liquids. To ensure effective analysis, flow visualization techniques must adapt to the advancements in the field of fluid dynamics that benefits substantially from the growing computational power of both commodity desktops and supercomputers on the one hand, and steadily expanding knowledge about fluid physics on the other. A prominent example of these advances can be found in the research of two-phase flow with liquid droplets and jets, where high performance computation and sophisticated algorithms for phase tracking enable well resolved and physically accurate simulations of liquid dynamics. Yet, the field of two-phase flow has remained largely unexplored in visualization research so far, leaving the scientists and engineers with a number of challenges when analyzing the data. These include the difficulty in tracking and investigating topological events in large droplet groups, high complexity of droplet dynamics due to the involved interfaces, and a limited choice of high quality interactive methods for the analysis of related transport phenomena. It is therefore the aim of this thesis to address these challenges by providing a multi-scale approach for the visual investigation of two-phase flow, with the focus on the analysis of droplet interaction, fluid interfaces, and material transport. To address the problem of analyzing highly complex two-phase flow simulations with droplet groups and jets, a linked-view approach with three-dimensional and abstract space-time graph representation of droplet dynamics is proposed. The interactive brushing and linking allows for general exploration of topological events as well as detailed inspection of dynamics in terms of oscillations and rotations of droplets. Another approach further examines the separation of liquid phases by segmenting liquid volumes according to their topological changes in future time. For visualization, boundary surfaces of these volume segments are extracted that reveal intricate details of droplet topology dynamics. Additionally, within this framework, visualization of advected particles corresponding to arbitrarily selected segment provides useful insights into the spatio-temporal evolution of the segment. The analysis of interfaces is necessary to understand the interplay of interface dynamics and the dynamics of droplet interactions. A commonly used technique for interface tracking in the volume of fluid-based simulations is the piecewise linear approximation which, although accurate, can affect the quality of the simulation results. To study the influence of the interface reconstruction on the phase tracking procedure, a visualization method is presented that extracts the interfaces by means of the first-order Taylor approximation, and provides several derived quantities that help assess the simulation results in relation to the interface reconstruction quality. The liquid interface is further investigated from the physical standpoint with an approach based on quantities derived from velocity and surface tension gradients. The developed method supports examination of surface tension forces and their impact on the interface instability, as well as detailed analysis of interface deformation characteristics. A line of research important for engineering applications is the analysis of electric fields on droplet interfaces. It is, however, complicated by higher-order elements used in the simulations to preserve field discontinuities. A visualization method has been developed that correctly visualizes these discontinuities at material boundaries. Additionally, the employed space-time representation of the droplet-insulator contact line reveals characteristics of electric field dynamics. The dynamics of droplets are often examined assuming single-phase flow, for instance when the internal material transport is of interest. From the visualization perspective, this allows for adaption of traditional vector field visualization techniques to the investigation of the studied phenomena. As one such concept, dye based visualization is proposed that extends the transport analysis to advection-diffusion problems, therefore revealing true transport behavior. The employed high quality advection preserves fine details of the dye, while the implementation on graphics processing units ensures interactive visualization. Several streamline-based concepts are applied in space-time representation of 2D unsteady flow. By interpreting time as the third spatial dimension, many 3D streamline-based visualization techniques can be applied to investigate 2D unsteady flow. The introduced vortex core ribbons support the examination of vortical flow behavior by revealing rotation near the core lines. For the study of topological structures, a method has been developed that extracts separatrices implicitly as boundaries of regions with different flow behavior, and therefore avoids potentially complicated explicit extraction of various topological structures. All proposed techniques constitute a novel multi-scale approach for visual analysis of two-phase flow. The analysis of droplet interactions is addressed with visualization of the phenomena leading to breakups and with detailed visual inspection of these breakups. On the interface level, techniques for the interface analysis give insights into the simulation quality, mechanisms behind topology changes, as well as the behavior of electrically charged droplets. Further down the scale, the dye-based visualization, streamline-based concepts for space-time analysis, and the implicit extraction of flow topology allow for the investigation of droplet internal transport as well as general single-phase flow scenarios. The applicability of the proposed methods extends, in a varying degree, beyond the use in two-phase flow. Their usability is demonstrated on data from simulations based on Navier-Stokes equations that exemplify practical problems in the research of fluid dynamics. Note de contenu : Introduction 1 - Fundamentals and State of the Art 2 - Visualization of Interactions in Droplet Groups 3 - Visualization of Liquid Interface Dynamics 4 - Visualization Approaches for Material Transport Conclusion Numéro de notice : 21572 Affiliation des auteurs : non IGN Nature : Thèse étrangère Note de thèse : Doktor thesis : Sciences naturelles : Stuttgart : 2017 En ligne : https://elib.uni-stuttgart.de/handle/11682/9701 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90563

Development of a SGM-based multi-view reconstruction framework for aerial imagery / Mathias Rothermel (2016)  

Public Titre : Development of a SGM-based multi-view reconstruction framework for aerial imagery Type de document : Thèse/HDR Auteurs : Mathias Rothermel, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 2016 Autre Editeur : Stuttgart : University of Stuttgart Collection : DGK - C, ISSN 0065-5325 num. 792 Importance : 115 p. ISBN/ISSN/EAN : 978-3-7696-5204-8 Note générale : bibliographie PhD dissertation Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] appariement d'images [Termes IGN] carte de profondeur [Termes IGN] image aérienne [Termes IGN] image aérienne oblique [Termes IGN] image oblique [Termes IGN] modèle numérique de surface [Termes IGN] pas d'échantillonnage au sol [Termes IGN] reconstruction 3D [Termes IGN] scène [Termes IGN] SURE Résumé : (auteur) Advances in the technology of digital airborne camera systems allow for the observation of surfaces with sampling rates in the range of a few centimeters. In combination with novel matching approaches, which estimate depth information for virtually every pixel, surface reconstructions of impressive density and precision can be generated. Therefore, image based surface generation meanwhile is a serious alternative to LiDAR based data collection for many applications. Surface models serve as primary base for geographic products as for example map creation, production of true-ortho photos or visualization purposes within the framework of virtual globes. The goal of the presented theses is the development of a framework for the fully automatic generation of 3D surface models based on aerial images - both standard nadir as well as oblique views. This comprises several challenges. On the one hand dimensions of aerial imagery is consider-able and the extend of the areas to be reconstructed can encompass whole countries. Beside scalability of methods this also requires decent processing times and efficient handling of the given hardware resources. Moreover, beside high precision requirements, a high degree of automation has to be guaranteed to limit manual interaction as much as possible. Due to the advantages of scalability, a stereo method is utilized in the presented thesis. The approach for dense stereo is based on an adapted version of the semi global matching (SGM) algorithm. Following a hierarchical approach corresponding image regions and meaningful disparity search ranges are identified. It will be verified that, dependent on undulations of the scene, time and memory demands can be reduced significantly, by up to 90% within some of the conducted tests. This enables the processing of aerial datasets on standard desktop machines in reasonable times even for large fields of depth. Stereo approaches generate disparity or depth maps, in which redundant depth information is available. To exploit this redundancy, a method for the refinement of stereo correspondences is proposed. Thereby redundant observations across stereo models are identified, checked for geometric consistency and their reprojection error is minimized. This way outliers are removed and precision of depth estimates is improved. In order to generate consistent surfaces, two algorithms for depth map fusion were developed. The first fusion strategy aims for the generation of 2.5D height models, also known as digital surface models (DSM). The proposed method improves existing methods regarding quality in areas of depth discontinuities, for example at roof edges. Utilizing benchmarks designed for the evaluation of image based DSM generation we show that the developed approaches favorably compare to state-of-the-art algorithms and that height precisions of few GSDs can be achieved. Furthermore, methods for the derivation of meshes based on DSM data are discussed. The fusion of depth maps for 3D scenes, as e.g. frequently required during evaluation of high resolution oblique aerial images in complex urban environments, demands for a different approach since scenes can in general riot be represented as height fields. Moreover, depths across depth maps possess varying precision and sampling rates due to variances in image scale, errors in orientation and other effects. Within this thesis a median-based fusion methodology is proposed. By using geometry-adaptive triangulation of depth maps depth-wise normal arc extracted and, along the point coordinates are filtered and fused using tree structures. The outputs of this method are oriented points which then can be used to generate meshes. Precision and density of the method will be evaluated using established multi-view benchmarks. Beside the capability to process close range datasets, results for large oblique airborne data sets will be presented. The report closes with a summary, discussion of limitations and perspectives regarding improvements and enhancements. The implemented algorithms are core elements of the commercial software package SURE, which is freely available for scientific purposes. Numéro de notice : 17371 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère Note de thèse : Dissertation : Photogrammetrische Bildverarbeitung : Stuttgart : 2016 En ligne : https://elib.uni-stuttgart.de/handle/11682/9067 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=84247

GPS time-variable seasonal signals modeling / Qiang Chen (2015)  

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3D visualization of multivariate data / Harald Sanftmann (2012)  

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Ein modulares Simulationskonzept zur Evaluierung von Positionssensoren sowie Filter- und Regelalgorithmen am Beispiel des automatisierten Strassenbaus / A. Beetz (2012)  

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Automatic recognition and 3D reconstruction of buildings from digital imagery / Babak Ameri Shahrabi (2000)  

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GPS - network analysis / Wojciech Pachelski (1988)

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PUMA / W. Lindlohr (1988)

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Geodetic network adjustment using GPS triple difference observations and a priori stochastic information / K. Eren (1987)

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