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Isostatic stability of the East Antarctic station Dumont d'Urville from long-term geodetic observations and geophysical models / Martine Amalvict in Polar research, vol 28 n° 2 (August 2009)
[article]
Titre : Isostatic stability of the East Antarctic station Dumont d'Urville from long-term geodetic observations and geophysical models Type de document : Article/Communication Auteurs : Martine Amalvict, Auteur ; Pascal Willis , Auteur ; Guy Wöppelmann , Auteur ; Eric Ivins, Auteur ; Marie-Noëlle Bouin , Auteur ; Laurent Testut, Auteur ; Jacques Hinderer, Auteur Année de publication : 2009 Article en page(s) : pp 193 - 202 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Antarctique
[Termes IGN] coordonnées GPS
[Termes IGN] déformation verticale de la croute terrestre
[Termes IGN] données géophysiques
[Termes IGN] rebond post-glaciaireRésumé : (auteur) Geodetic measurements of the vertical crustal displacement collocated with absolute gravity changes provide a discriminatory measurement of present-day glacial changes, versus more deeply seated rock motions caused by glacial isostatic adjustment (GIA). At the East Antarctic station of Dumont d'Urville, we compare the displacements derived from continuous DORIS (1993.0–2006.0) and Global Positioning System (GPS) (1999.0–2005.7) data, and observed changes in absolute gravity (2000–2006), with the predicted vertical displacement and change in gravity from GIA modelling. The geodetic results have mutual self-consistency, suggest station stability and provide upper bounds on both GIA and secular ice mass changes. The GIA models tend to predict amplitudes of rock motion larger than those observed, and we conclude that this part of Antarctica is probably experiencing a slight gain in ice mass, in contrast to West Antarctica. Numéro de notice : A2009-579 Affiliation des auteurs : IGN+Ext (1940-2011) Thématique : POSITIONNEMENT Nature : Article DOI : 10.1111/j.1751-8369.2008.00091.x En ligne : http://doi.org/10.1111/j.1751-8369.2008.00091.x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=88648
in Polar research > vol 28 n° 2 (August 2009) . - pp 193 - 202[article]An adaptive approach to topographic feature extraction from Digital Terrain Models / Y. Song in Photogrammetric Engineering & Remote Sensing, PERS, vol 75 n° 3 (March 2009)
[article]
Titre : An adaptive approach to topographic feature extraction from Digital Terrain Models Type de document : Article/Communication Auteurs : Y. Song, Auteur ; J. Shan, Auteur Année de publication : 2009 Article en page(s) : pp 281 - 290 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique
[Termes IGN] Antarctique
[Termes IGN] carte des pentes
[Termes IGN] extraction automatique
[Termes IGN] extraction de traits caractéristiques
[Termes IGN] modèle numérique de terrain
[Termes IGN] seuillageRésumé : (Auteur) This study presents an adaptive solution to topographic feature extraction from digital terrain model. First, a slope map is produced by the proposed slope estimator that combines the well-known D8 and finite difference methods. In the second step, the Laplacian of Gaussian (LOG) operator with multiple thresholds is applied to the resultant slope map to determine edge pixels that have local maximum curvature and maximum connectivity. The third step adopts the original and robust marching square algorithms to trace the topographic features. Modification is made to selectively introduce shoulder points according to the local topographic complexity. In comparison to the existing algorithms, the performance of the proposed adaptive marching square algorithm is evaluated in terms of precision and resolution of the extracted features. Digital terrain models over three locations in Antarctica are used for this study. It is shown overall reducing 75 percent of the shoulder points from the robust algorithm will cause 24 percent precision drop in the adaptive method. Copyright ASPRS Numéro de notice : A2009-038 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.14358/PERS.75.3.281 En ligne : https://doi.org/10.14358/PERS.75.3.281 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29668
in Photogrammetric Engineering & Remote Sensing, PERS > vol 75 n° 3 (March 2009) . - pp 281 - 290[article]
Titre : Regional gravity field modelling with radial basis functions Type de document : Thèse/HDR Auteurs : Tobias Wittwer, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2009 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 72 Importance : 190 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-315-0 Note générale : Bibliographie
Document téléchargeable sur le site de NCG : voir lien dans la noticeLangues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] Antarctique
[Termes IGN] Canada
[Termes IGN] champ de pesanteur local
[Termes IGN] données GOCE
[Termes IGN] données GRACE
[Termes IGN] factorisation de Cholesky
[Termes IGN] filtre de Wiener
[Termes IGN] fonction de base radiale
[Termes IGN] Groenland
[Termes IGN] harmonique sphérique
[Termes IGN] levé gravimétrique
[Termes IGN] modèle de géopotentiel
[Termes IGN] modèle mathématiqueIndex. décimale : 30.42 Gravimétrie Résumé : (Auteur) Terrestrial gravimetry, airborne gravimetry, and the recent dedicated satellite gravity missions Challenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and Gravity and Ocean Circulation Explorer (GOCE) provide us with high-quality, high-resolution gravity data, which are used in many application areas such as
1. the computation of global static gravity fields, in support of precise orbit determination of many Earth observation satellites;
2. the quantification and interpretation of mass transport in the Earth system such as the shrinking of ice sheets, the shifting of ocean currents, and water storage variations;
3. the computation of high resolution regional and local gravity fields in support of height system realisation and the modelling of reservoirs and geophysical features.
Traditionally, for each data set (satellite, airborne, terrestrial) dedicated data processing schemes have been developed using different estimation principles, parametrisations, etc. The optimal combination of different data sets would benefit of a methodology that can be used for any type of data. Elements of this methodology comprise a uniform parametrisation, estimation principle, data weighting scheme, regularisation, and error propagation.
In the framework of this thesis, such a methodology is developed. It uses radial basis functions (RBFs) as parametrisation. They have parameters that allow us to tune their approximation properties as function of the data coverage and distribution and the signal variations. This makes them equally well suited for global and local parametrisation. Moreover, there exists an analytical relationship between a spherical harmonic representation and a radial basis function representation, which allows the latter to be transformed into the former, without any approximation error. Among others, this has the advantage that one can make use of existing processing tools, such as spectral analysis.
Although radial basis functions are not new in gravity field modelling, there are many important issues which have not yet been addressed or require further research. The main research question underlying this thesis is: "Are radial basis functions a suitable parametrisation for global and regional models of the mean and time-variable gravity field, and if so, how do they perform compared with spherical harmonic solutions?" Directly related to this is the question: "Are there situations where radial basis functions models outperform spherical harmonic solutions?" The answer to both questions is positive as will be shown in this thesis.
There are two important aspects that determine the quality of a gravity field model based on radial basis functions: 1) the spatial distribution of the radial basis functions, i.e. the basis function network design, and 2) the choice of the bandwidths of the radial basis functions. For both problems, semi-automatic algorithms have been developed. Data-adaptive network design and local refinement avoid respectively over- and under-parametrisation by fine-tuning the basis function network based on the data. The basis function bandwidth is determined by optimising the fit to the data including control data.
The computation of regional gravity fields constitutes a considerable numerical workload, especially since the methodology presented here does not use an iterative normal equation solver (e.g., the preconditioned conjugate gradient method). Instead, a Cholesky solver is used, which requires the assembly of the complete normal equation system. For this purpose the program is numerically optimised and fully parallelised for hybrid high performance computer architectures. This guarantees optimal performance on all types of parallel computers and handles the memory requirements.
The modelling of satellite data with radial basis functions is investigated using real data of the GRACE satellites collected over the period 2003-2006. An optimal Wiener filter has been developed for radial basis functions in line with the optimal Wiener filter approach previously developed at DEOS for spherical harmonic representations. Monthly GRACE gravity models computed using radial basis function are compared to spherical harmonic models, and validated using independent data provided by the Ice Cloud and Land Elevation Satellite (ICESat), radar altimetry satellites, and the global hydrological model PCR-GLOBWB. Two applications were considered: 1) mass variations over Greenland and Antarctica and 2) water storage variations in river basins. The results show that the radial basis function approach yields solutions that are of at least the same quality as global models using spherical harmonics. There is evidence that radial basis functions may provide better spatial resolution and more realistic amplitudes in particular in high-latitude areas. For instance, it will be shown that radial basis function solutions detected signal that could not be seen in spherical harmonic solutions.
Two test areas are used for regional gravity field modelling using real terrestrial data: An area in the northeastern USA and a larger area in eastern Canada. The results show that the data-adaptivity and local refinement algorithms developed in the framework of this thesis provide good solutions of constant quality regardless of the initially chosen grid spacing. The models are compared to the official regional geoid models GEOID03 and CGG05, respectively. In both cases, rms errors of several centimetres remain, which are attributed to different input data and processing strategies.
The combination of satellite and terrestrial data is tested using simulated global and regional data sets. It is shown that a joint inversion of the two data sets yields combined solutions which are significantly better than a solution using the traditional remove-restore approach. The addition of satellite data with the corresponding stochastic model compensates the reduced quality of the terrestrial data at long wavelengths.
The examples show that the regional modelling methodology presented here is a very flexible approach that can be applied to all types of gravity data and data distributions, regardless of application, data source, and area size. The quality of the solutions is at least equal to the solutions developed for the stand-alone inversion of individual data sets, while radial basis functions offer numerical benefits. As a result, this approach is already used for marine geoid modelling, and recommended for the modelling of airborne gravity data and data of the GOCE satellite, and for the joint inversion of satellite, airborne and ground-based gravity data.Note de contenu : Nomenclature
1 Introduction
1.1 Background
1.2 Motivation
1.2.1 Regional modelling from satellite data
1.2.2 Regional modelling from terrestrial data
1.2.3 Combined modelling of satellite and terrestrial data
1.2.4 Radial basis functions
1.3 Prior research on radial basis functions
1.4 Research objectives
1.5 Outline of thesis
2 Radial basis functions
2.1 Gravity field representations
2.1.1 Spherical harmonics
2.1.2 Radial basis functions
2.2 RBF types and behaviour in the spectral domain
2.3 Behaviour in the spatial domain
2.4 Relation of RBFs to a spherical harmonic representation
2.5 Choice of RBF characteristics
2.5.1 Choice of the kernel
2.5.2 Bandwidth selection
2.6 RBF network design
2.6.1 Grids
2.6.2 Adaptation to data
2.6.3 Local refinement
2.7 Multi-scale modelling
2.7.1 Introduction
2.7.2 Methodology
2.7.3 Filtering
3 Mathematical model and estimation principle
3.1 Functional model
3.2 Stochastic model
3.3 Least-squares estimation and regularisation
3.4 Solution strategies
3.4.1 Cholesky factorisation
3.4.2 Conjugate gradients
3.5 Variance component estimation .
3.5.1 Normal equations
3.5.2 Variance component estimation
3.5.3 Stochastic trace estimation
4 Numerical aspects
4.1 Numerical optimisation
4.1.1 Constant expressions in "do"-loops
4.1.2 Computation of the design matrix
4.1.3 Normalisation of coordinates
4.1.4 Normalisation of basis functions
4.2 Fast synthesis
4.3 Parallelisation
4.3.1 Problem description
4.3.2 Parallel computer architectures .
4.3.3 Parallelisation for shared memory computers
4.3.4 Parallelisation for distributed memory computers
4.3.5 Hybrid parallelisation
4.3.6 Results of parallelisation
4.4 Summary and conclusions
5 Gravity field modelling from satellite data
5.1 Functional model
5.1.1 Three-point range combination approach
5.1.2 Residual accelerations
5.1.3 Equivalent water heights
5.1.4 Trend and signal amplitude estimation
5.2 Stochastic model
5.3 Optimal filtering
5.3.1 Introduction
5.3.2 Signal covariance matrix computation
5.3.3 Noise level estimation
5.4 RBF network design
5.4.1 Grid choice
5.4.2 Data-adaptivity and local refinement
5.4.3 Parametrised area
5.5 Bandwidth selection
5.6 Results.
5.6.1 Comparison of unfiltered RBF and spherical harmonic solution
5.6.2 Models used for comparison
5.6.3 Recovery of ice mass loss in Greenland and Antarctica
5.6.4 Recovery of terrestrial water storage variations
5.7 Summary and conclusions
6 Local gravity field modelling from terrestrial data
6.1 Functional model
6.1.1 Functional model for gravity disturbances
6.1.2 Functional model for gravity anomalies
6.1.3 Functional model for height anomalies
6.2 RBF network design
6.2.1 Grid choice
6.2.2 Data-adaptivity and local refinement
6.2.3 Parametrised area
6.3 Bandwidth selection
6.4 Results
6.4.1 Northeastern USA
6.4.2 Canada
6.5 Summary and conclusions
7 Combined modelling of satellite and terrestrial data
7.1 Combination strategies
7.1.1 Remove-restore approach
7.1.2 High-pass filtering
7.1.3 Direct combination
7.1.4 Combination with satellite-only solution
7.2 RBF network design and bandwidth selection
7.3 Results
7.3.1 Global test
7.3.2 Regional test
7.4 Summary and conclusions
8 Summary, conclusions and recommendations
8.1 Summary and conclusions
8.2 Recommendations for further researchNuméro de notice : 15511 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : PhD thesis 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=62744 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15511-01 30.42 Livre Centre de documentation Géodésie Disponible Designing sound in cybercartography: from structured cinematic narratives to unpredictable sound-image interactions / Sébastien Caquard in International journal of geographical information science IJGIS, vol 22 n°11-12 (november 2008)
[article]
Titre : Designing sound in cybercartography: from structured cinematic narratives to unpredictable sound-image interactions Type de document : Article/Communication Auteurs : Sébastien Caquard, Auteur ; Glenn Brauen, Auteur ; B. Wright, Auteur ; P. Jasen, Auteur Année de publication : 2008 Article en page(s) : pp 1219 - 1245 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géomatique
[Termes IGN] acoustique
[Termes IGN] Antarctique
[Termes IGN] atlas numérique
[Termes IGN] bruit (audition)
[Termes IGN] carte auditive
[Termes IGN] cartographie par internetRésumé : (Auteur) In this paper, we draw on the analysis of sound in film theory in order to explore the potential that sound offers cybercartography. We first argue that the theoretical body developed in film studies is highly relevant to the study of sound/image relationships in mapmaking. We then build on this argument to develop experimental animated and interactive sound maps for the Cybercartographic Atlas of Antarctica that further explore the potential of sound for integrating emotional, cultural and political dimensions in cartography. These maps have been designed to recreate cinematic soundscapes, to provide contrapuntal perspectives on the cartographic image and to generate an aural identity of the atlas. As part of this experimental mapping, an innovative sound infrastructure is being developed to allow complex sound designs to be transmitted over the Internet as part of atlas content. Through this infrastructure, the user can select as well as contribute his own sounds. The overall cartographic message is becoming less predictable, thus opening new perspectives on the way we design, interact with, and modify sounded maps over the Internet. Copyright Taylor & Francis Numéro de notice : A2008-401 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1080/13658810801909649 En ligne : https://doi.org/10.1080/13658810801909649 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29393
in International journal of geographical information science IJGIS > vol 22 n°11-12 (november 2008) . - pp 1219 - 1245[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 079-08071 RAB Revue Centre de documentation En réserve L003 Disponible 079-08072 RAB Revue Centre de documentation En réserve L003 Disponible Polar Radar for Ice Sheet Measurements (PRISM) / S. Gogineni in Remote sensing of environment, vol 111 n° 2-3 (30 November 2007)
[article]
Titre : Polar Radar for Ice Sheet Measurements (PRISM) Type de document : Article/Communication Auteurs : S. Gogineni, Auteur ; D. Braaten, Auteur ; et al., Auteur Année de publication : 2007 Article en page(s) : pp 204 - 211 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection
[Termes IGN] Antarctique
[Termes IGN] calotte glaciaire
[Termes IGN] épaisseur de la glace
[Termes IGN] glaciologie
[Termes IGN] Groenland
[Termes IGN] image radar
[Termes IGN] morphologie glaciaire
[Termes IGN] onde décimétriqueRésumé : (Auteur) We provide an overview of a project to develop and demonstrate radars for imaging the ice-bed interface, mapping shallow and deep internal layers, and measuring ice thickness. We developed an ultra-wideband very high-frequency (VHF) radar (120 to 300 MHz) for simultaneously measuring ice thickness, mapping internal layers at depth, and imaging the ice-bed interface, and an ultra high-frequency (UHF) ultra-wideband radar (500 to 2000 MHz) for fine-resolution mapping of near-surface internal layers. We used these radars to collect data at Summit Camp, Greenland, during July 2005, and the West Antarctic Ice Sheet (WAIS) deep drill core site during January 2006. These results provide us with an unprecedented view of basal characteristics and internal layers. We also developed an outreach program, a communications system, and rovers to facilitate geophysical measurements in the future. Copyright Elsevier Numéro de notice : A2007-487 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2007.01.022 En ligne : https://doi.org/10.1016/j.rse.2007.01.022 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28850
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