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Auteur X. Wu |
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Affiner la recherche Interroger des sources externesThree-Corner Hat for the assessment of the uncertainty of non-linear residuals of space-geodetic time series in the context of terrestrial reference frame analysis / Claudio Abbondanza in Journal of geodesy, vol 89 n° 4 (April 2015)
Titre : Three-Corner Hat for the assessment of the uncertainty of non-linear residuals of space-geodetic time series in the context of terrestrial reference frame analysis Type de document : Article/Communication Auteurs : Claudio Abbondanza, Auteur ; Zuheir Altamimi Année de publication : 2015 Article en page(s) : pp 313-329 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] co-positionnement
[Termes IGN] corrélation temporelle
[Termes IGN] estimation de cohérence
[Termes IGN] hauteur ellipsoïdale
[Termes IGN] incertitude de position
[Termes IGN] International Terrestrial Reference Frame
[Termes IGN] série temporelle
[Termes IGN] signal GPSRésumé : (auteur) We discuss the application of the Three-Corner Hat (TCH) to time series of space-geodetic station position residuals with the purpose of characterizing the uncertainties of GPS, VLBI, SLR, DORIS for the International Terrestrial Reference Frame (ITRF) determination. Adopting simulations, we show that, in the absence of time-correlated errors, TCH is able to fully recover the nominal uncertainties of groups of observations whose intrinsic precisions are remarkably dissimilar to one another, as is the case for the space-geodetic techniques. When time-correlated errors are predominant, as it happens with GPS, TCH is affected by the increased variance of the observations and its estimates are positively biased. TCH applied to 16 ITRF co-located sites confirms that GPS, albeit affected by time-correlated errors, is the most precise of the space-geodetic techniques. GPS median uncertainties are 1.1, 1.2 and 2.8 mm, for the north, east and height component, respectively. VLBI performs particularly well in the horizontal component, the median uncertainties being ≈2 mm. The height component is ∼3 times larger than the GPS one. SLR and DORIS median uncertainties exceed by far the 7 mm level on all of the three components. Comparing TCH results with station position repeatabilities, we find that the two metrics are in striking agreement for VLBI and DORIS, but not for SLR and GPS. The inconsistencies between TCH and station repeatabilities for co-located GPS and SLR point to the presence of either specific station-dependent biases or low-quality co-locations. Scaling factors derived adopting the ratio between TCH and median formal errors on the positions suggest the station position covariances have to be up-scaled for VLBI, SLR, DORIS and down-scaled for GPS. Numéro de notice : A2015-340 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0777-x Date de publication en ligne : 18/11/2014 En ligne : https://doi.org/10.1007/s00190-014-0777-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76709
in Journal of geodesy > vol 89 n° 4 (April 2015) . - pp 313-329[article]
Titre : External evaluation of the Terrestrial Reference Frame: report of the task force of the IAG sub-commission 1.2 Type de document : Article/Communication Auteurs : Xavier Collilieux Editeur : Berlin, Heidelberg, Vienne, New York, ... : Springer Année de publication : 2014 Collection : International Association of Geodesy Symposia, ISSN 0939-9585 num. 139 Conférence : IAG 2011, General Assembly 28/06/2011 02/07/2011 Melbourne Australie Proceedings Springer Importance : pp 197 - 202 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] International Terrestrial Reference FrameRésumé : (auteur) Ideally, the origin of the Terrestrial Reference Frame (TRF) is defined as the center of mass of the whole Earth system, the time evolution of its orientation is such that no global net rotation of the whole Earth’s surface is possible and the TRF scale is specified through the adoption of some physical constants and time-scale. These parameters need to be accurately determined since their choice has an influence on many Earth’s science applications. The aim of the task force “External evaluation of the Terrestrial Reference Frame” is to review all the applications for which the TRF accuracy is of fundamental importance. As the TRF choice has an influence on the interpretation of the results in these specific applications, we investigate if some evaluation procedures could be established. We classified the methods that allow evaluation of the TRF using ground, geodetic data or models that have not been used in the TRF construction, based on their expected contributions. Some of these methods have been applied to the latest International Terrestrial Reference System realizations and the results are presented here. Although further analysis will be necessary to deliver a more precise error budget, our findings demonstrate that the most recent realizations of the ITRS are more accurate than the previous in terms of origin and scale rate definition. The current level of ITRF2008 accuracy is likely to be at the level of 0.5 mm/year along each origin component and better than 0.3 mm/year in the scale rate according to the most recent studies. Numéro de notice : C2011-026 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : 10.1007/978-3-642-37222-3_25 Date de publication en ligne : 06/10/2013 En ligne : http://dx.doi.org/10.1007/978-3-642-37222-3_25 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=78509
Titre : Accuracy of the International Terrestrial Reference Frame origin and Earth expansion Type de document : Article/Communication Auteurs : X. Wu, Auteur ; Xavier Collilieux Année de publication : 2011 Article en page(s) : 5 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] International Terrestrial Reference FrameRésumé : (auteur) The International Terrestrial Reference Frame (ITRF) is a fundamental datum for high‐precision orbit tracking, navigation, and global change monitoring. Accurately realizing and maintaining ITRF origin at the mean Earth system center of mass (CM) is critical to surface and spacecraft based geodetic measurements including those of sea level rise and its sources. Although ITRF combines data from satellite laser ranging (SLR), Very Long Baseline Interferometry (VLBI), Global Positioning System (GPS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), its origin is currently realized by the single technique of SLR. Consequently, it is difficult to independently evaluate the origin accuracy. Also, whether the solid Earth is expanding or shrinking has attracted persistent attention. The expansion rate, if any, has not been accurately determined before, due to insufficient data coverage on the Earth's surface and the presence of other geophysical processes. Here, we use multiple precise geodetic data sets and a simultaneous global estimation platform to determine that the ITRF2008 origin is consistent with the mean CM at the level of 0.5 mm yr−1, and the mean radius of the Earth is not changing to within 1σ measurement uncertainty of 0.2 mm yr−1. Numéro de notice : A2011-590 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2011GL047450 Date de publication en ligne : 08/07/2011 En ligne : https://doi.org/10.1029/2011GL047450 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90909
in Geophysical research letters > vol 38 n° 13 (July 2011) . - 5 p.[article]
Titre : Effect of the satellite laser ranging network distribution on geocenter motion estimation Type de document : Article/Communication Auteurs : Xavier Collilieux Année de publication : 2009 Article en page(s) : 17 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] fonction de Green
[Termes IGN] géocentre
[Termes IGN] masse de la Terre
[Termes IGN] série temporelle
[Termes IGN] télémétrie laser sur satelliteRésumé : (auteur) SLR network translations estimated between a quasi-instantaneous station position set, theoretically expressed with respect to the center of mass of the Earth (CM), and a secular reference frame are the signature of the motion of the CM with respect to the Earth crust. Geocenter motion is defined here to be the motion of the CM with respect to the geometric center of the solid Earth surface (CF). SLR translational variations cannot be rigorously interpreted as identical to geocenter motion due to the sparse and nonuniform distribution of the SLR network. Their difference is called the network effect, which should be dominated at subdecadal timescales by loading signals.We have computed translation time series of the SLR network using two independent geophysically based loading models. One is a displacement model estimated from surface fluid data (Green’s function approach), called forward model, and the other is a displacement model estimated from GPS and ocean bottom pressure (OBP) data, called inverse model. The translation models have been subtracted from their respective geocenter motion models computed from degree-1 mass load coefficients in order to evaluate their network effect biases. Scatter due to the SLR network effect is at the level of 1.5 mm RMS. It could slightly shift the phase of the annual SLR geocenter motion estimate by less than 1 month and could affect X and Z annual geocenter motion amplitudes at the 1-mm level, which is about one third of the expected signal. Two distinct methods are suggested to account for network effect when comparing SLR translations to geocenter motion models. The first is to add the network effect term predicted by a displacement model to the geocenter motion loading model. The second relies on an adequate combination of SLR and GPS products to estimate SLR translation that could be better compared with geocenter motion. Numéro de notice : A2009-531 Affiliation des auteurs : IGN+Ext (1940-2011) Thématique : POSITIONNEMENT Nature : Article DOI : 10.1029/2008JB005727 Date de publication en ligne : 07/04/2009 En ligne : http://dx.doi.org/10.1029/2008JB005727 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83525
in Journal of geophysical research : Solid Earth > Vol 114 n° B4 (April 2009) . - 17 p.[article]Documents numériques
en open access
Effect of the satellite laser ranging networkAdobe Acrobat PDF
Titre : A new approach to quantifying spatial contiguity using graph theory and spatial interaction Type de document : Article/Communication Auteurs : X. Wu, Auteur ; Alan T. Murray, Auteur Année de publication : 2008 Article en page(s) : pp 387 - 407 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Analyse spatiale
[Termes IGN] interaction spatiale
[Termes IGN] paysage
[Termes IGN] théorie des graphes
[Termes IGN] voisinage (relation topologique)Résumé : (Auteur) Spatial contiguity is an important and fundamental landscape property in land allocation, habitat design, and forest management. The agreed upon notion of contiguity in the literature suggests shapelessness. However, existing approaches for measuring/promoting contiguity use proxies that either favour a particular shape or ignore inter-patch relationships in fragmented landscapes. We propose an unbiased relative measure of contiguity ranging from zero to one based on graph theory and spatial interaction. The new measure reflects intra-patch and inter-patch relationships by quantifying contiguity within patches and potential contiguity among patches. Empirical analysis suggests that this measure of contiguity is reliable, consistent, and insensitive to sub-region shape. Copyright Taylor & Francis Numéro de notice : A2008-146 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1080/13658810701405615 En ligne : https://doi.org/10.1080/13658810701405615 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29141
in International journal of geographical information science IJGIS > vol 22 n° 4-5 (april 2008) . - pp 387 - 407[article]Exemplaires(2)
Code-barres Cote Support Localisation Section Disponibilité 079-08031 RAB Revue Centre de documentation En réserve L003 Disponible 079-08032 RAB Revue Centre de documentation En réserve L003 Disponible Anwendungen der satellitengestützten Radarinterferometrie zur Bestimmung von Topographie und Geschwindig-keitsfeldern / X. Wu (1998)
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