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Observed changes in the Earth’s dynamic oblateness from GRACE data and geophysical models / Y. Sun in Journal of geodesy, vol 90 n° 1 (January 2016)  

Public [article]  inJournal of geodesy > vol 90 n° 1 (January 2016) . - pp 81 - 89 Titre : Observed changes in the Earth’s dynamic oblateness from GRACE data and geophysical models Type de document : Article/Communication Auteurs : Y. Sun, Auteur ; Pavel Ditmar, Auteur ; Riccardo Riva, Auteur Année de publication : 2016 Article en page(s) : pp 81 - 89 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] données laser [Termes IGN] données TLS (télémétrie) [Termes IGN] incertitude des données [Termes IGN] masse d'eau [Termes IGN] rebond post-glaciaire Résumé : (auteur) A new methodology is proposed to estimate changes in the Earth’s dynamic oblateness (ΔJ2 or equivalently, −5√ΔC20) on a monthly basis. The algorithm uses monthly Gravity Recovery and Climate Experiment (GRACE) gravity solutions, an ocean bottom pressure model and a glacial isostatic adjustment (GIA) model. The resulting time series agree remarkably well with a solution based on satellite laser ranging (SLR) data. Seasonal variations of the obtained time series show little sensitivity to the choice of GRACE solutions. Reducing signal leakage in coastal areas when dealing with GRACE data and accounting for self-attraction and loading effects when dealing with water redistribution in the ocean is crucial in achieving close agreement with the SLR-based solution in terms of de-trended solutions. The obtained trend estimates, on the other hand, may be less accurate due to their dependence on the GIA models, which still carry large uncertainties. Numéro de notice : A2016-020 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0852-y En ligne : https://doi.org/10.1007/s00190-015-0852-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79467 [article]

Analysis of star camera errors in GRACE data and their impact on monthly gravity field models / Pedro Inácio in Journal of geodesy, vol 89 n° 6 (June 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 6 (June 2015) . - pp 551 - 571 Titre : Analysis of star camera errors in GRACE data and their impact on monthly gravity field models Type de document : Article/Communication Auteurs : Pedro Inácio, Auteur ; Pavel Ditmar, Auteur ; Roland Klees, Auteur ; Hassan Hashemi Farahani, Auteur Année de publication : 2015 Article en page(s) : pp 551 - 571 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] acquisition de données [Termes IGN] analyse diachronique [Termes IGN] anomalie de pesanteur [Termes IGN] capteur spatial [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] erreur de mesure [Termes IGN] impact sur les données [Termes IGN] modèle d'erreur [Termes IGN] orientation du capteur [Termes IGN] propagation d'erreur Résumé : (auteur) Star cameras (SCs) on board the GRACE satellites provide information about the attitudes of the spacecrafts. This information is needed to reduce the K-band ranging data to the centre of mass of the satellites. In this paper, we analyse GRACE SC errors using two months of real data of the primary and secondary SCs. We show that the errors consist of a harmonic component, which is highly correlated with the satellite’s true anomaly, and a stochastic component. We built models of both error components, and use these models for error propagation studies. Firstly, we analyse the propagation of SC errors into inter-satellite accelerations. A spectral analysis reveals that the stochastic component exceeds the harmonic component, except in the 3–10 mHz frequency band. In this band, which contains most of the geophysically relevant signal, the harmonic error component is larger than the random component. Secondly, we propagate SC errors into optimally filtered monthly mass anomaly maps and compare them with the total error. We found that SC errors account for about 18 % of the total error. Moreover, gaps in the SC data series amplify the effect of SC errors by a factor of 5. Finally, an analysis of inter-satellite pointing angles for GRACE data between 2003 and 2010 reveals that inter-satellite ranging errors were exceptionally large during the period February 2003 till May 2003. During these months, SC noise is amplified by a factor of 3 and is a considerable source of errors in monthly GRACE mass anomaly maps. In the context of future satellite gravity missions, the noise models developed in this paper may be valuable for mission performance studies. Numéro de notice : A2015-350 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0797-1 Date de publication en ligne : 03/03/2015 En ligne : https://doi.org/10.1007/s00190-015-0797-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76724 [article]

The static gravity field model DGM-1S from GRACE and GOCE data: computation, validation and an analysis of GOCE mission’s added value / Hassan Hashemi Farahani in Journal of geodesy, vol 87 n° 9 (September 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 9 (September 2013) . - pp 843 - 867 Titre : The static gravity field model DGM-1S from GRACE and GOCE data: computation, validation and an analysis of GOCE mission’s added value Type de document : Article/Communication Auteurs : Hassan Hashemi Farahani, Auteur ; Pavel Ditmar, Auteur ; R. Klees, Auteur Année de publication : 2013 Article en page(s) : pp 843 - 867 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GOCE [Termes IGN] données GRACE [Termes IGN] gradiométrie [Termes IGN] modèle de géopotentiel Résumé : (Auteur) We present a global static model of the Earth’s gravity field entitled DGM-1S based on GRACE and GOCE data. The collection of used data sets includes nearly 7 years of GRACE KBR data and 10 months of GOCE gravity gradient data. The KBR data are transformed with a 3-point differentiation into quantities that are approximately inter-satellite accelerations. Gravity gradients are processed in the instrumental frame. Noise is handled with a frequency-dependent data weighting. DGM-1S is complete to spherical harmonic degree 250 with a Kaula regularization being applied above degree 179. Its performance is compared with a number of other satellite-only GRACE/GOCE models by confronting them with (i) an independent model of the oceanic mean dynamic topography, and (ii) independent KBR and gravity gradient data. The tests reveal a competitive quality for DGM-1S. Importantly, we study added value of GOCE data by comparing the performance of satellite-only GRACE/GOCE models with models produced without GOCE data: either ITG-Grace2010s or EGM2008 depending on which of the two performs better in a given region. The test executed based on independent gravity gradients quantifies this added value as 25–38 % in the continental areas poorly covered with terrestrial gravimetry data (Equatorial Africa, Himalayas, and South America), 7–17 % in those with a good coverage with these data (Australia, North America, and North Eurasia), and 14 % in the oceans. This added value is shown to be almost entirely related to coefficients below degree 200. It is shown that this gain must be entirely attributed to gravity gradients acquired by the mission. The test executed based on an independent model of the mean dynamic topography suggests that problems still seem to exist in satellite-only GRACE/GOCE models over the Pacific ocean, where noticeable deviations between these models and EGM2008 are detected, too. Numéro de notice : A2013-565 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-013-0650-3 Date de publication en ligne : 12/07/2013 En ligne : https://doi.org/10.1007/s00190-013-0650-3 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32701 [article]

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Estimation of mass change trends in the Earth’s system on the basis of GRACE satellite data, with application to Greenland / C. Siemes in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 69 - 87 Titre : Estimation of mass change trends in the Earth’s system on the basis of GRACE satellite data, with application to Greenland Type de document : Article/Communication Auteurs : C. Siemes, Auteur ; Pavel Ditmar, Auteur ; et al., Auteur Année de publication : 2013 Article en page(s) : pp 69 - 87 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] bilan de masse [Termes IGN] calotte glaciaire [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] filtre de Wiener [Termes IGN] gravimétrie spatiale [Termes IGN] Groenland [Termes IGN] harmonique sphérique [Termes IGN] isostasie [Termes IGN] levé gravimétrique [Termes IGN] matrice de covariance Résumé : (Auteur) The Gravity Recovery and Climate Experiment (GRACE) satellite mission measures the Earth’s gravity field since March 2002. We propose a new filtering procedure for post-processing GRACE-based monthly gravity field solutions provided in the form of spherical harmonic coefficients. The procedure is tuned for the optimal estimation of linear trends and other signal components that show a systematic behavior over long time intervals. The key element of the developed methodology is the statistically optimal Wiener-type filter which makes use of the full covariance matrices of noise and signal. The developed methodology is applied to determine the mass balance of the Greenland ice sheet, both per drainage system and integrated, as well as the mass balance of the ice caps on the islands surrounding Greenland. The estimations are performed for three 2-year time intervals (2003–2004, 2005–2006, and 2007–2008), as well as for the 6-year time interval (2003–2008). The study confirms a significant difference in the behavior of the drainage systems over time. The average 6-year rate of mass loss in Greenland is estimated as 165 + 15 Gt/year. The rate of mass loss of the ice caps on Ellesmere Island (together with Devon Island), Baffin Island, Iceland, and Svalbard is found to be 22 + 4, 21 + 6, 17 + 9, and 6 + 2 Gt/year, respectively. All these estimates are corrected for the effect of glacial isostatic adjustment. Numéro de notice : A2013-071 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0580-5 Date de publication en ligne : 12/07/2012 En ligne : https://doi.org/10.1007/s00190-012-0580-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32209 [article]

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