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Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations / Pieter N.A.M. Visser in Journal of geodesy, vol 88 n° 11 (November 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 11 (November 2014) . - pp 1029 - 1046 Titre : Assessment of observing time-variable gravity from GOCE GPS and accelerometer observations Type de document : Article/Communication Auteurs : Pieter N.A.M. Visser, Auteur ; W. Van der Wal, Auteur ; E.J. Schrama, Auteur ; et al., Auteur Année de publication : 2014 Article en page(s) : pp 1029 - 1046 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] données GOCE [Termes IGN] données GPS [Termes IGN] effet atmosphérique [Termes IGN] gravimétrie spatiale [Termes IGN] orbite [Termes IGN] variable Résumé : (Auteur) An assessment has been made of the possibility to estimate time-variable gravity from GPS-derived orbit perturbations and common-mode accelerometer observations of ESA’s GOCE Earth Explorer. A number of 20-day time series of Earth’s global long-wavelength gravity field have been derived for the period November 2009 to November 2012 using different parameter setups and estimation techniques. These techniques include a conventional approach where for each period, one set of gravity coefficients is estimated, either excluding or including empirical accelerations, and the so-called Wiese approach where higher frequency coefficients are estimated for the very long wavelengths. A principal component analysis of especially the time series of gravity field coefficients obtained by the Wiese approach and the conventional approach with empirical accelerations reveals an annual signal. When fitting this annual signal directly through the time series, the sine component (maximum in spring) displays features that are similar to well-known continental hydrological mass changes for the low latitude areas, such as mass variations in the Amazon basin, Africa and Australia for spatial scales down to 1,500 km. The cosine component (maximum in winter), however, displays large signals that can not be attributed to actual mass variations in the Earth system. The estimated gravity field changes from GOCE orbit perturbations are likely affected by missing GPS observations in case of high ionospheric perturbations during periods of increased solar activity, which is minimal in Summer and maximal towards the end of autumn. Numéro de notice : A2014-563 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0741-9 Date de publication en ligne : 27/06/2014 En ligne : https://doi.org/10.1007/s00190-014-0741-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=74749 [article]

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Variance component estimation uncertainty for unbalanced data: application to a continent-wide vertical datum / M. S. Filmer in Journal of geodesy, vol 88 n° 11 (November 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 11 (November 2014) . - pp 1081-1093 Titre : Variance component estimation uncertainty for unbalanced data: application to a continent-wide vertical datum Type de document : Article/Communication Auteurs : M. S. Filmer, Auteur ; Will E. Featherstone, Auteur ; S.J. Claessens, Auteur Année de publication : 2014 Article en page(s) : pp 1081-1093 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] analyse de variance [Termes IGN] continent [Termes IGN] incertitude des données [Termes IGN] système de référence géodésique Résumé : (Auteur) Variance component estimation (VCE) is used to update the stochastic model in least-squares adjustments, but the uncertainty associated with the VCE-derived weights is rarely considered. Unbalanced data is where there is an unequal number of observations in each heterogeneous data set comprising the variance component groups. As a case study using highly unbalanced data, we redefine a continent-wide vertical datum from a combined least-squares adjustment using iterative VCE and its uncertainties to update weights for each data set. These are: (1) a continent-wide levelling network, (2) a model of the ocean’s mean dynamic topography and mean sea level observations, and (3) GPS-derived ellipsoidal heights minus a gravimetric quasigeoid model. VCE uncertainty differs for each observation group in the highly unbalanced data, being dependent on the number of observations in each group. It also changes within each group after each VCE iteration, depending on the magnitude of change for each observation group’s variances. It is recommended that VCE uncertainty is computed for VCE updates to the weight matrix for unbalanced data so that the quality of the updates for each group can be properly assessed. This is particularly important if some groups contain relatively small numbers of observations. VCE uncertainty can also be used as a threshold for ceasing iterations, as it is shown—for this data set at least—that it is not necessary to continue time-consuming iterations to fully converge to unity. Numéro de notice : A2014-564 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0744-6 Date de publication en ligne : 24/07/2014 En ligne : https://doi.org/10.1007/s00190-014-0744-6 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=74750 [article]

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Comparison of individual and combined zenith tropospheric delay estimations during CONT08 campaign / Arnaud Pollet in Journal of geodesy, vol 88 n° 11 (November 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 11 (November 2014) . - pp 1095 - 1112 Titre : Comparison of individual and combined zenith tropospheric delay estimations during CONT08 campaign Type de document : Article/Communication Auteurs : Arnaud Pollet , Auteur ; David Coulot , Auteur ; Olivier Bock , Auteur ; Samuel Nahmani , Auteur Année de publication : 2014 Article en page(s) : pp 1095 - 1112 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] International Earth Rotation Service [Termes IGN] propagation troposphérique [Termes IGN] retard troposphérique zénithal Résumé : (Auteur) CONT campaigns are 2-week campaigns of continuous VLBI observations. The IERS working group on combination at the observation level uses these campaigns to study such combinations. In this work, combinations of DORIS, GPS, SLR, and VLBI technique measurements are studied during CONT08. We present different results concerning the use of common zenith tropospheric delay (ZTD) during the combination. We compare the ZTD obtained separately using each individual technique data processing, the combined ZTD, and the ZTD derived from a meteorological model. This resulted in a high level of consistency between each of these ZTD at a sub-centimeter level, a consistency which especially depends on the number of observations per estimated ZTD and the humidity level in the troposphere. We noted that GPS provides the main information about the combined ZTD, the other techniques providing complementary information when a lack of GPS observations occurs. Numéro de notice : A2014-565 Affiliation des auteurs : LASTIG LAREG (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0745-5 Date de publication en ligne : 30/07/2014 En ligne : https://doi.org/10.1007/s00190-014-0745-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=74751 [article]

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