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Geospatial data on the web / Linda Van Den Brink (2018)  

Public Titre : Geospatial data on the web Type de document : Thèse/HDR Auteurs : Linda Van Den Brink, Auteur ; Jantien E. Stoter, Directeur de thèse Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2018 Autre Editeur : Delft [Pays-Bas] : Delft University of Technology Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 Importance : 232 p. Format : 21 x 30 cm Note générale : bibliographie Dissertation for the purpose of obtaining the degree of doctor at Delft University of Technology Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique web [Termes IGN] accès aux données localisées [Termes IGN] acquisition de données [Termes IGN] CityGML [Termes IGN] diffusion de données [Termes IGN] données hétérogènes [Termes IGN] données localisées [Termes IGN] données multisources [Termes IGN] données topographiques [Termes IGN] harmonisation des données [Termes IGN] interopérabilité [Termes IGN] outil d'aide à la décision [Termes IGN] RDF [Termes IGN] recherche d'information géographique [Termes IGN] réutilisation des données [Termes IGN] similitude sémantique [Termes IGN] web des données Résumé : (auteur) Geospatial data is an increasingly important information asset for decisionmaking, from simple every day decisions like where to park your car, to national and international policy on topics like infrastructure and environment. Because of the location aspect, geospatial data is often the linking pin between different datasets and therefore important for data integration. A lot of geospatial data is created, for example, as part of governmental processes and nowadays, also disseminated as open data, traditionally through "Spatial data infrastructures" (SDIs). There is a lot of potential for reusing this data in other domains than the domain and use case for which it was originally created. My main research question was: "How to reuse geospatial data, from different, heterogeneous sources, via the web across communities?". Several aspects of data dissemination must be addressed before open data is actually in a good position for getting reused. These aspects have been coined the "FAIR principles": findability, accessibility, interoperability, and reusability. Note de contenu : 1- Introduction, research questions and methodology 2- Definition and establishment of a national 3D standard 3- Semantic Harmonisation 4- Geospatial Linked Data 5- Web of Data 6- Discussion, Conclusion and Future work Numéro de notice : 21836 Affiliation des auteurs : non IGN Autre URL associée : https://repository.tudelft.nl/islandora/object/uuid%3Aa0bd364d-f101-4337-91c5-92038b2a6d56?collection=research Thématique : GEOMATIQUE/SOCIETE NUMERIQUE Nature : Thèse étrangère Note de thèse : PhD thesis : 3D Geo-Information : TU Delft : 2018 DOI : 10.4233/uuid:a0bd364d-f101-4337-91c5-92038b2a6d56 En ligne : https://www.ncgeo.nl/index.php/en/publicatiesgb/publications-on-geodesy/item/278 [...] Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91364

Global Earth structure recovery from state-of-the-art models of the Earth’s gravity field and additional geophysical Information / K. Hamayun (2014)  

Public Titre : Global Earth structure recovery from state-of-the-art models of the Earth’s gravity field and additional geophysical Information Type de document : Thèse/HDR Auteurs : K. Hamayun, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2014 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 85 Importance : 165 p. ISBN/ISSN/EAN : 978-94-6186-325-6 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] anomalie de pesanteur [Termes IGN] champ de pesanteur terrestre [Termes IGN] données CHAMP [Termes IGN] données géophysiques [Termes IGN] données GOCE [Termes IGN] données GRACE [Termes IGN] levé gravimétrique Résumé : (auteur) Currently, a tremendous improvement is observed in the accuracy and spatial resolution of global Earth’s gravity field models. This improvement is achieved due to using various new data, including those from satellite gravimetry missions (CHAMP, GRACE, and GOCE); terrestrial and airborne gravity data, as well as altimetry data. The new gravity field models can be applied, in particular, to improve our knowledge of the Earth’s interior structure. The aim of this study is to compile a global map of the Moho interface using a global gravity model and additional available information about the crust density structure. In our study, we use the gravity field model EIGEN-6C2 and the global crustal model CRUST1.0 derived from seismic data. In addition, we utilize seismic-based models of Moho as prior information: CRUST1.0 model, as well as the Crust07 model, which was derived by a fully non-linear inversion of fundamental mode surface waves. The observed gravity field contains nuisance signals from the topography and density heterogeneities related to bathymetry, ice, sediments, and other crustal components. Therefore, we model and sequentially subtract these signals by applying so-called stripping corrections. This results in crust-stripped gravity field quantities (gravity anomalies and gravity disturbances). In the course of research, we review different analytical, semi-analytical, and numerical forward modeling techniques to compute the gravitational attraction of a body. We also derive an analytical formula for the computation of gravitational potential generated by a polyhedral body having linearly varying density. We compute the correction to observed gravity field using the analytical methods in the vicinity of the body and using semi-analytical methods in the far zone. We demonstrate that the sequential correction of gravity disturbances and gravity anomalies for nuisance signals increases the correlation with the Moho depths. We use the corrected gravity field to find the global (mean) value for the crust-mantle density contrast using the Pearson’s correlation method. We use an empirical technique in which the absolute correlation between the Moho depth from CRUST 1.0 model and the updated crust stripped gravity disturbances/anomalies is minimized. The updated stripped gravity disturbances/anomalies are obtained by adding a contribution (attraction) related to the density contrast between the reference crust and the upper most mantle to stripped gravity disturbances/anomalies. [...] Numéro de notice : 14852 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.4233/uuid:f8f6d8cd-9a6e-4ad1-8152-8d164c1055c9 En ligne : https://doi.org/10.4233/uuid:f8f6d8cd-9a6e-4ad1-8152-8d164c1055c9 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75698

Acquisition of 3D topography / Sander J. Oude Elberink (2010)  

Public Titre : Acquisition of 3D topography : automated 3D road and building reconstruction using airborne laser scanner data and topographic maps Type de document : Thèse/HDR Auteurs : Sander J. Oude Elberink, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2010 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 74 Importance : 172 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-318-1 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie [Termes IGN] bati [Termes IGN] carte topographique [Termes IGN] données laser [Termes IGN] données localisées 3D [Termes IGN] lasergrammétrie [Termes IGN] modèle 3D de l'espace urbain [Termes IGN] reconstruction 3D [Termes IGN] reconstruction 3D du bâti [Termes IGN] réseau routier [Termes IGN] télémétrie laser aéroporté Résumé : (Auteur) Introduction and research goal : Our research covers the automation in acquiring three dimensional (3D) topographic objects. The research tasks focus on two specific objects: roads and buildings. These objects are of high importance in 3D city models as they are two major topographic classes in the urban environment. Our activities are located between: -1. how topographic objects exist in reality; -2. how they are captured in the data, and -3. how they appear in a modelled/virtual world. To accomplish an automated approach, existing 2D topographic maps are upgraded to 3D using airborne laser scanner data. 3D topography also includes multiple heights or even multiple objects on top of each other at a certain location. The essence in the research activities on roads differs basically from those on buildings. For roads the focus is on reconstructing the edges' height of the objects, whereas for buildings the challenge is to reconstruct the 3D polyhedral roof shape inside the building edges. 3D Road reconstruction : When examining 3D road objects, we can expect that multiple road objects cross at a certain location. An automated method for 3D modelling of complex highway interchanges is presented. Laser data and 2D topographic map data are combined in an innovative 3D reconstruction procedure. Complex situations demand for knowledge to guide the automatic reconstruction. This knowledge is used in the fusion procedure to constrain the topological and geometrical properties of the reconstructed 3D model. Laser data has been segmented and filtered before it is fused with map data. In the surface-growing algorithm combining map and laser points, the laser data is assigned to the corresponding road element. Elevations of map points are determined by least squares plane fitting through a selection of neighbouring laser points. Although results are shown using two specific data sources, the algorithm is designed to be capable of dealing with any polygon-based topographic map and any aerial laser scanner data set. Quality analysis is essential for developing a reliable reconstruction process and for a proper use of 3D data. The quality of 3D reconstructed roads strongly depends on accuracy and type of input data and the reconstruction processing steps. We predict the precision of reconstructed map elevations by propagating errors in the input data through the processing steps. Besides this quality prediction, we test the reconstructed model against independent reference data. Differences between these two datasets are explained by the predicted uncertainty in the model. Map point heights can be reconstructed with an average precision of 10 to 15 cm, depending on the laser point configuration. 3D. Building reconstruction : The building reconstruction task contains three main goals: -1. to select laser points belonging to building roofs, -2. to detect the roof structure of that building, and -3. to reconstruct the outlines of the roof. We present a building reconstruction approach, which is based on a target graph matching algorithm as intermediate step to relate laser data with building models. Establishing this relation is important for adding building knowledge to the data. Our targets are topological representations of the most common roof structures which are stored in a database. Laser data is segmented into planar patches. The segments that are selected in the segment-in-polygon algorithm are considered initial roof segments. Topological relations between segments, in terms of intersection lines and height jumps, are represented in a building roof graph. These relations are labelled according to their geometry and that of the segments (e.g. same/opposite normal direction, convex/concave, tilted/horizontal). This graph is matched with the graphs from the target database. Matching results describe which target objects appear topologically in the data. Our target based graph matching algorithm supports the first two goals. The matching algorithm performs a filtering task: data features that topologically correspond with common roof structures are considered to be part of the roof structure of that building. These data features will be transferred to our automated building reconstruction, where the outlines of the roof faces have to be reconstructed. Segments and intersection lines that do not fit to an existing target roof topology will be removed from the further automated reconstruction approach. The reconstruction algorithm covers the third main goal of our building reconstruction task. For the geometric reconstruction, we present two approaches that vary in the amount of information they take from the data. The first, more data driven approach starts with laser data features that have been matched with target models. In general, the matched intersection lines represent the interior of the roof structure, so the task is to find an appropriate solution for the remaining roof edges, e.g. eaves and gutters. Map data is used for selection of roof segments and is taken as location for walls. Therefore we need to split up map polygons in order to build walls that distinguish various height levels, e.g. at step edge locations. The second, more model driven approach reconstructs parameterised building models. This approach relies more on geometric assumptions, such as roof symmetry, but the models can be refined if the data deviates significantly from the model. The target information includes the details on how these deviations are determined and on the thresholds to decide what is significant or not. We present results of 3D reconstructed models, including several quality checks. These quality measures describe the completeness of the match results plus the correctness of assumptions to the roof outline. About 20% of the buildings are affected by segments that did not completely match with the target graphs. In a few of these cases, this is correct because the segment is not representing a roof face. However, in about 40% of these cases, a neighbouring segment that would complete a target match is missing. Adapting processing parameters, such as minimum segment size, may improve the result but it may also disturb other topological relations. Setting the parameters is therefore an important task for the operator. Specially, parameters that define the segmentation algorithm are crucial as the segment is the key data feature in our building reconstruction algorithm. In order to improve our matching algorithm, the likelihood of relations between segments could be included in the attribute list of edges in the roof topology graph. At the moment only information on the geometric appearance of the intersection line is given as attribute value to the corresponding graph edge. Future work includes defining likelihood functions for graph edges and analysing the effect of likelihood attributes. Note de contenu : Part 1: Introduction to acquisition of 3D topography 1 Introduction 1.1 3D Topography 1.2 Scope and limitations 1.3 Input data 1.4 Research problems 1.5 Goal and objectives 1.6 Importance 1.7 Thesis outline 2 Use of 3D topography 2.1 Introduction 2.2 User requirements 2.2.1 Municipality of Den Bosch 2.2.2 Survey Department of Rijkswaterstaat 2.2.3 Water board "Hoogheemraadschap de Stichtsche Rijnlanden" 2.2.4 Topographic Service of the Dutch Cadastre 2.3 Re-using 3D models 2.3.1 Municipality of Den Bosch 2.3.2 Survey Department of Rijkswaterstaat 2.3.3 Water board "Hoogheemraadschap de Stichtsche Rijnlanden" 2.3.4 Topographic Service of the Dutch Cadastre 2.3.5 Availability and distribution 2.3.6 Data fusion 2.3.7 Generalization and filtering 2.3.8 3D Represents as-is situation 2.4 Role of use cases in research project 2.5 Recent developments in using 3D topography 2.6 Conclusions Part 2: 3D Roads 3 3D Reconstruction of roads 3.1 Introduction 3.2 Related work 3.2.1 Road reconstruction from aerial images 3.2.2 2D Road mapping from laser data 3.2.3 3D Reconstruction from laser data 3.3 Proposed approach 3.4 Data sources 3.4.1 Airborne laser scanner data 3.4.2 Pre-processing laser data 3.4.3 2D Topographic map data 3.4.4 Pre-processing 2D map 3.5 Fusion of map and laser data 3.5.1 Research problems on fusing map and laser data 3.5.2 Proposed fusion algorithm 3.6 3D Reconstruction of polygons 3.6.1 Polygon boundaries 3.6.2 Additional polygons 3.6.3 Assumptions on boundaries 3.6.4 Surfaces 3.7 Results 3.7.1 Interchange "Prins Clausplein" 3.7.2 Interchange "Waterberg" 3.8 Discussion 3.8.1 Parameter settings 3.8.2 Topological correctness 4 Quality analysis on 3D roads 4.1 Error propagation 4.1.1 Quality of plane at map point location 4.1.2 Quality of laser block 4.1.3 Quality of plane model 4.2 Reference data 4.2.1 Height differences between reference data and 3D model 4.3 Testing of predicted quality 4.4 Discussion Part 3: 3D Buildings 5 Building shape detection 5.1 Introduction 5.1.1 Real buildings vs 3D model representation 5.1.2 Real buildings vs appearance in input data 5.1.3 Appearance in input data vs 3D model representation 5.2 Related work 5.2.1 2D Mapping of building outlines 5.2.2 3D Reconstruction of buildings 5.3 Research problems 5.3.1 Problems on roof shape detection 5.3.2 Problems on scene complexity 5.4 Proposed approach 5.5 Information from map data 5.6 Features from laser data 5.6.1 Segmentation of laser scanner data 5.6.2 Intersection lines 5.6.3 Step edges 5.6.4 Roof topology graph 5.7 Target graphs 5.8 Target based graph matching 5.9 Complete matching results 5.10 Incomplete matching results 6 3D Building Reconstruction 6.1 Introduction 6.2 Components of a roof boundary 6.3 Approach 1: Combine features from complete match results 6.4 Extension of horizontal intersection lines 6.5 Outer boundaries of roof faces 6.5.1 Flat roof faces 6.5.2 Eave construction 6.5.3 Gutter construction 6.6 Dormers and step edges 6.6.1 Simple dormers 6.6.2 Step edges 6.6.3 Step edges for map subdivision 6.7 Reconstruction of walls 6.8 Approach 2: reconstructed targets 6.8.1 Parameterised target models 6.8.2 Use of map data 6.8.3 Limitations 6.8.4 Potential use 6.9 Summary 7 Results and evaluation 7.1 Introduction 7.2 Results 7.2.1 Approach 1: Combined features 7.2.2 Approach 2: Reconstructed targets 7.3 Evaluation 7.3.1 Laser data features 7.3.2 Evaluation on target based matching 7.3.3 Reconstructed models 7.3.4 Problematic situations 7.3.5 Performance in time 7.4 Potential for nation wide 3D building database 7.5 Summary Part 4: Conclusions and recommendations 8 Conclusions and recommendations 8.1 Conclusions 8.1.1 3D Topographic object reconstruction 8.1.2 3D Road reconstruction 8.1.3 3D Building reconstruction 8.2 Recommendations Numéro de notice : 10833 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse étrangère DOI : sans En ligne : https://www.ncgeo.nl/index.php/en/publicatiesgb/publications-on-geodesy/item/258 [...] Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62510

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Assessing spatial data infrastructures / L. Grus (2010)

Public Titre : Assessing spatial data infrastructures Type de document : Monographie Auteurs : L. Grus, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2010 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 76 Importance : 170 p. Format : 16 x 24 cm ISBN/ISSN/EAN : 978-90-6132-320-4 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Infrastructure de données [Termes IGN] analyse comparative [Termes IGN] infrastructure nationale des données localisées [Termes IGN] qualité des données [Termes IGN] structure de données localisées Résumé : (Auteur) Over the last two decades many countries throughout the world have taken steps to establish national Spatial Data Infrastructures (SDls). These actions have sought to provide an infrastructure for accessing and sharing spatial data to reduce the duplication of spatial data collection by both users and producers, and enable better utilization of spatial data and associated services. When developing SDI initiatives it is increasingly important to assess their outcomes in order to justify the resources spent on those infrastructures. Many researchers throughout the world have been struggling with the issue of assessing SDls. The task is difficult due to complex, dynamic and constantly evolving nature of SDI. The main objective of this thesis is to develop a framework for assessing Spatial Data Infrastructures. This main objective is divided into four sub-objectives: 1. to analyse SDI complexity; 2. to develop a SDI assessment framework; 3. to evaluate the developed SDI assessment framework; 4. to expand the developed SDI Assessment Framework by adding an assessment view for a goal-oriented SDI assessment. Each of these sub-objectives are analyzed in chapters 2 -5. Chapter 2 analyses SDI complexity by determining whether SDls can be viewed as Complex Adaptive Systems (CAS). This was done by analyzing three NSDI case studies and conducting a survey among SDI experts. First, it was determined if CAS features and behaviours could be found in the three analyzed NSDls. The author searched for the following CAS features and behaviours: 1) features: components, complexity, sensitivity to initial conditions, openness, unpredictability and scale independence; 2) behaviours: adaptability, selforganization, non-linear behaviour, feedback loop mechanism. Second, a survey among SDI experts was conducted by asking them to express their strength of support regarding the presence of CAS features and behaviours in general SDI concept. The results reveal that SDls can be viewed as CAS. Chapter 3 develops a SDI assessment framework. First, the key SDI characteristics that underlie the problems affecting SDI assessment were identified and analyzed. In order to deal with these problems the principles of assessing Complex Adaptive Systems were identified and discussed. The principles of evaluating Complex Adaptive Systems and norms of general evaluation theory were the basis for developing an assessment framework. The principles of assessing CAS, among others, require that the assessment framework is flexible, contains multiple assessment approaches and uses various methods to determine the indicators' values. The result is the Multi-view SDI assessment framework. Chapter 4 evaluates the Multi-view SDI assessment framework. The evaluation was based on the pilot application of the framework in 21 National SDIs. The evaluation focused on the process of framework application and framework's applicability to assess SDIs. The process of framework application was evaluated against two criteria: 1) NSDI coordinator response time; 2) Completeness of data. The applicability of the framework to assess SDIs was evaluated by sending a questionnaire to 21 NSDI coordinators. The coordinators were asked for the opinion about the applicability of Multi-view SDI assessment framework application results to assess SDIs. The questionnaire was based on meta-evaluation standard criteria for conducting evaluations (Stufflebeam, 1974; The Joint Committee, 1994). The results showed that the framework could be applied to assess 21 NSDIs. The evaluation of the application process revealed that the completeness of assessment data and time needed to measure indicators depends strongly on the assessment methods used. In addition, the results showed that significant part of the measurements contained missing values. Finally it was demonstrated that the users tend to agree with the general applicability of the Multi-view SDI assessment framework to assess SDIs. Chapter 5 expands the developed SDI Assessment Framework by adding an assessment view for a goal-oriented SDI assessment. The conceptual foundation of the developed assessment view was a goal-attainment assessment model presented by Hansen (2005). The model seeks to answer the question: to what degree has the goals been realized? The model derives the assessment criteria from goals. To develop a goal-oriented assessment view the author used the Multi-view SDI assessment framework. The developed assessment view was tested by applying it to measure the goals' realization of the Dutch SDI. In addition, the potential users of the goal-oriented assessment view evaluated it. The main result of this chapter is the view for assessing the extent to which SDIs realize their goals. The implementation of the proposed view in the Dutch SDI case demonstrates its potential application. In addition, the evaluation of the proposed view conducted among the potential users confirms its usability and generic character. It is also argued that the precision of definition of SDI goals determines how easy the correct assessment indicators can be found. Chapter 6 discusses the results of the thesis, presents author's reflections on the main results, and suggests recommendations for the future research. In order to better assess SDIs researchers should look for theories, which could explain and help to understand SDI mechanisms and laws. The results show that viewing SDI as CAS is beneficial for better understanding of SDI assessment principles. As a result, the Multi-view SDI assessment framework is proposed. However, due to the practical reasons it is hypothesized that a fully comprehensive SDI assessment might never be achieved. The reflections on the thesis results lead to several conclusions. Firstly, viewing SDI as CAS, apart from helping to assess SDIs, has also a potential to significantly improve the conceptualization of SDI. Secondly, the proposed Multi-view SDI assessment framework demonstrates the potential value for SDI assessment users acting on all SDI organizational levels. Thirdly, the experience of developing an assessment framework for SDI may also be used in evaluation discipline to further analyze and propose solutions for assessing complex phenomena. Fourthly, the proposed framework has also potential to contribute to an emerging trend of the inter- and transdisciplinary approaches to researching and assessing SDIs. The following recommendations for the future research are made: 1) Analyze the roles that CAS features and behaviours play in SDIs; 2) Focus on developing operational SDI assessment approaches suited to specific user's needs; 3) Analyze the users and their requirements of SDI assessment; 4) Analyze the use of SDI assessment results. Note de contenu : 1. General Introduction 2. Spatial Data Infrastructures as Complex Adaptive Systems 3. Multi-view SDI Assessment Framework 4. Evaluation of the Multi-view SDI Assessment Framework 5. An assessment view to evaluate whether Spatial Data Infrastructures meet their goals 6. General Discussion 123 References Appendices Numéro de notice : 10446 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62445

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Identification and modelling of sea level change contributors on GRACE satellite gravity data and their applications to climate monitoring / Bert Wouters (2010)

Public Titre : Identification and modelling of sea level change contributors on GRACE satellite gravity data and their applications to climate monitoring Type de document : Monographie Auteurs : Bert Wouters, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2010 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 73 Importance : 182 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-316-7 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] champ de pesanteur terrestre [Termes IGN] changement climatique [Termes IGN] GRACE [Termes IGN] Groenland [Termes IGN] niveau moyen des mers [Termes IGN] surveillance météorologique Résumé : (Auteur) Recently, the Intergovernmental Panel on Climate Change named sea level rise as one of the major challenges of the 21st century. Given the high population density of coastal regions, a small rise of the sea level will have a substantial impact on human society. However, the Earth's climate system is a complex matter arid model predictions of the sea level changes likely to be expected in the coming century currently show a wide spread. Clearly, a thorough understanding of present-day climate variability is imperative narrow this uncertainty band, which on its turn depends on the availability of accurate and detailed observations of our climate. A valuable contribution to the expanding array of satellites dedicated to observations of the Earth System, are the Gravity Recovery and Climate Experiment (GRACE) satellites, launched in March 2002. This mission is dedicated to observing changes of the Earth's gravity field at (sub-)monthly intervals. At time-scales of a few years, these changes are mostly related to the redistribution of water on the Earth's surface. For example, a thinning of the Greenland ice sheet will manifest itself as a local negative anomaly in the gravity field, whereas the water that is added to the ocean will show up as a predominantly positive anomaly. The main objective of this dissertation is to study how the GRACE observations can be used to improve our knowledge of changes in the Earth's climate systems, and how the data should be processed in order to optimize quality and spatial resolution. The GRACE data provided by the science teams consist of spherical harmonic coefficients. They show particular correlations between coefficients of identical order and even and odd degree, respectively, due to the mission's architecture and deficiencies in the background models used throughout the processing of the satellite measurements. These noise artifacts show up as striping patterns along the north-south direction in the monthly maps of surface mass changes, hampering the interpretation of the observations. In this dissertation, it is shown that empirical orthogonal function (EOF) analysis is an effective method to reduce the noise in the GRACE data. This statistical tool separates a data set into a number of characteristic (eigen) modes of variance, in combination with an index describing the amplitude of the mode in time, i.e. the principal components. The EOF analysis can be applied to the maps of surface mass changes, in which case the first few modes are related to the annual and long-term trend components. The fourth mode appears to be related to the El Nino/Southern Oscillation. The noise signals arc absorbed by the higher modes, which makes the leading modes largely stripe-free up to a resolution of approximately 400 kilometers. A further reduction of the noise can be obtained by applying the EOF de-composition directly to the spherical harmonic coefficients, after grouping them following order. The principal components arc compared to a random process and, if the two arc statistically sufficiently alike, not used in the further data processing. A series of tests shows that this approach reduces the noise by 60-80 %, compared the non-filtered case. An important feature of this filter is that it does not alter the shape of the signal and causes less reduction its power, compared to other commonly used filter methods based on the approach of Swenson and Walir (2006). Using the filtered data, changes in the mass content of the ocean have been studied. The GRACE satellites are capable of capturing seasonal changes in the ocean mass content accurately on a global scale. In combination with sea surface height observations made by satellite altimeter, the steric sea level component (related to changes in the heat and salinity content of the ocean) can be separated as well. A comparison with reference data sets shows that locally a coherent signal can be obtained at a (Gaussian) resolution of approximately 500 km over the oceans. These steric changes dominate the sea level in most of the oceans, but strong ocean bottom pressure fluctuations are observed in several areas, e.g., the Gulf of Carpentaria and the Gulf of Thailand. Estimates of long-term changes in the ocean mass and heat content arc a more challenging problem, and require a longer observation period and a better modeling of mass redistribution in the solid earth and the position of the center of mass of the Earth, two components to which the GRACE observations arc particularly sensitive. It is found that the global spherical harmonic coefficients contain more information than previously acknowledged. This is demonstrated by using the GRACE data to obtain a picture of the mass balance of the Greenland ice sheet at a regional scale. From the research in this dissertations, it shows that Greenland lost 179 Gigaton each year on average between 2003 and 2008, causing a global mean rise of sea level by 0.5 mm/yr. Comparing the trend in the first few to that in the last few years shows a speed-up of the thinning, which corroborates the picture of an increasingly negative mass balance of the ice sheet since the mid 1990's as indicated by, for example, regional climate models and radar altimetry observations. The majority of the losses occur in the coastal regions in the southeastern sector. The northwestern coastal zones were approximately in balance up to the summer of 2005, but show strong negative trends since. Large year-to-year differences in the mass balance of the ice sheet are observed, with a record loss in the warm summer of 2007. A strong correlation between the GRACE observations in summer and satellite measurements of surface melt area extent is demonstrated. Also, good agreement is found with regional climate modeling data, highlighting the potential of the GRACE observations to validate and improve the numerical models. A mass redistribution on land will cause a change in the shape of the global geoid. Sea level, when not acted upon by any other forcings, will adjust to this equipotential surface. Therefore, when water is exchanged between ocean and continents (and changes due to ocean dynamics are disregarded), sea level will not rise or fall uniformly, which is known as the so-called self-gravitation effect. Due to their global coverage, the GRACE observations of continental mass distribution are an excellent input to model this phenomenon. Strongest deviations from a uniform distribution are found off the coast of Alaska and in the Bay of Bengal, where differences of more than 100% are found on seasonal time-scales. In these regions, inclusion of the self-gravitation effect into numerical ocean model would result in a better agreement between modeled and observational data. From the work presented in this dissertation, it shows that the GRACE satellites are an invaluable tool for the monitoring of our climate system. Statistically filtering of the data reveals a wealth of information. In combination with altimetry observations, the GRACE data allows the separation of mass and steric components in sea level on seasonal time scales. Given a longer observational period and an improved understanding of the processes in the solid earth, expected to come available soon thanks to ESA's GOCE missions, long-term trends in these components will be identifiable. Furthermore, the GRACE mission allows us to put a constraint on the contribution of the Greenland ice sheet to present-day sea level rise. The technique to recover these changes can easily be expanded to other regions, such as the Antarctic or the Alaskan glacier fields. The synergy between GRACE data, future missions such as Cryosat-2, which will map height variations of the cryosphere with an unprecedented accuracy, and regional climate models, uncovering the physical processes behind the observed changes, promises a leap forward in our understanding of the mass balance of the ice sheets. Finally, com-paring the modeled deviations from uniform sea level changes with in-situ data such as from tide-gauges, may lead to a direct validation of the aforementioned self-gravitation theory with present-day data. Numéro de notice : 10335 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62396

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