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Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields / Mioara Mandea in Proceedings of the National Academy of Sciences of the United States of America PNAS, vol 109 n° 47 (November 2012)
[article]
Titre : Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields Type de document : Article/Communication Auteurs : Mioara Mandea, Auteur ; Isabelle Panet , Auteur ; Vincent Lesur, Auteur ; Olivier de Viron, Auteur ; Michel Diament , Auteur ; Jean-Louis Le Mouël, Auteur Année de publication : 2012 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] champ géomagnétique
[Termes IGN] données CHAMP
[Termes IGN] données GRACE
[Termes IGN] géocentre
[Termes IGN] variation temporelleRésumé : (Auteur) To understand the dynamics of the Earth’s fluid, iron-rich outer core, only indirect observations are available. The Earth’s magnetic field, originating mainly within the core, and its temporal variations can be used to infer the fluid motion at the top of the core, on a decadal and subdecadal time-scale. Gravity variations resulting from changes in the mass distribution within the Earth may also occur on the same time-scales. Such variations include the signature of the flow inside the core, though they are largely dominated by the water cycle contributions. Our study is based on 8 y of high-resolution, high-accuracy magnetic and gravity satellite data, provided by the CHAMP and GRACE missions. From the newly derived geomagnetic models we have computed the core magnetic field, its temporal variations, and the core flow evolution. From the GRACE CNES/GRGS series of time variable geoid models, we have obtained interannual gravity models by using specifically designed postprocessing techniques. A correlation analysis between the magnetic and gravity series has demonstrated that the interannual changes in the second time derivative of the core magnetic field under a region from the Atlantic to Indian Ocean coincide in phase with changes in the gravity field. The order of magnitude of these changes and proposed correlation are plausible, compatible with a core origin; however, a complete theoretical model remains to be built. Our new results and their broad geophysical significance could be considered when planning new Earth observation space missions and devising more sophisticated Earth’s interior models. Numéro de notice : A2012-735 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1073/pnas.1207346109 Date de publication en ligne : 10/09/2012 En ligne : https://doi.org/10.1073/pnas.1207346109 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91455
in Proceedings of the National Academy of Sciences of the United States of America PNAS > vol 109 n° 47 (November 2012)[article]Nontidal ocean loading: amplitudes and potential effects in GPS height time series / Tonie M. van Dam in Journal of geodesy, vol 86 n° 11 (November 2012)
[article]
Titre : Nontidal ocean loading: amplitudes and potential effects in GPS height time series Type de document : Article/Communication Auteurs : Tonie M. van Dam, Auteur ; Xavier Collilieux , Auteur ; Jan Wuite, Auteur ; Zuheir Altamimi , Auteur ; Jim Ray, Auteur Année de publication : 2012 Article en page(s) : pp 1043 - 1057 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] effet de charge
[Termes IGN] hauteurs de mer
[Termes IGN] masse
[Termes IGN] positionnement par GPS
[Termes IGN] série temporelle
[Termes IGN] surcharge océaniqueRésumé : (Auteur) Ocean bottom pressure (OBP) changes are caused by a redistribution of the ocean’s internal mass that are driven by atmospheric circulation, a change in the mass entering or leaving the ocean, and/or a change in the integrated atmospheric mass over the ocean areas. The only previous global analysis investigating the magnitude of OBP surface displacements used older OBP data sets (van Dam et al. in J Geophys Res 129:507–517, 1997). Since then significant improvements in meteorological forcing models used to predict OBP have been made, augmented by observations from satellite altimetry and expendable bathythermograph profiles. Using more recent OBP estimates from the Estimating the Circulation and Climate of the Ocean (ECCO) project, we reassess the amplitude of the predicted effect of OBP on the height coordinate time series from a global distribution of GPS stations. OBP-predicted loading effects display an RMS scatter in the height of between 0.2 and 3.7 mm, larger than previously reported but still much smaller (by a factor of 2) than the scatter observed due to atmospheric pressure loading. Given the improvement in GPS hardware and data analysis techniques, the OBP signal is similar to the precision of weekly GPS height coordinates. We estimate the effect of OBP on GPS height coordinate time series using the MIT reprocessed solution, mi1. When we compare the predicted OBP height time series with mi1, we find that the scatter is reduced over all stations by 0.1 mm on average with reductions as high as 0.7 mm at some stations. More importantly we are able to reduce the scatter on 65 % of the stations investigated. The annual component of the OBP signal is responsible for 80 % of the reduction in scatter on average. We find that stations located close to semi-enclosed bays or seas are affected by OBP loading to a greater extent than other stations. Numéro de notice : A2012-579 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0564-5 Date de publication en ligne : 06/05/2012 En ligne : https://doi.org/10.1007/s00190-012-0564-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32025
in Journal of geodesy > vol 86 n° 11 (November 2012) . - pp 1043 - 1057[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2012111 RAB Revue Centre de documentation En réserve L003 Disponible On computing ellipsoidal harmonics using Jekeli’s renormalization / J. Sebera in Journal of geodesy, vol 86 n° 9 (September 2012)
[article]
Titre : On computing ellipsoidal harmonics using Jekeli’s renormalization Type de document : Article/Communication Auteurs : J. Sebera, Auteur ; Johannes Bouman, Auteur ; W. Bosch, Auteur Année de publication : 2012 Article en page(s) : pp 713 - 726 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] Earth Gravity Model 2008
[Termes IGN] fonction hypergéométrique
[Termes IGN] harmonique ellipsoïdale
[Termes IGN] potentiel de pesanteur terrestre
[Termes IGN] transformation de LegendreRésumé : (Auteur) Gravity data observed on or reduced to the ellipsoid are preferably represented using ellipsoidal harmonics instead of spherical harmonics. Ellipsoidal harmonics, however, are difficult to use in practice because the computation of the associated Legendre functions of the second kind that occur in the ellipsoidal harmonic expansions is not straightforward. Jekeli’s renormalization simplifies the computation of the associated Legendre functions. We extended the direct computation of these functions—as well as that of their ratio—up to the second derivatives and minimized the number of required recurrences by a suitable hypergeometric transformation. Compared with the original Jekeli’s renormalization the associated Legendre differential equation is fulfilled up to much higher degrees and orders for our optimized recurrences. The derived functions were tested by comparing functionals of the gravitational potential computed with both ellipsoidal and spherical harmonic syntheses. As an input, the high resolution global gravity field model EGM2008 was used. The relative agreement we found between the results of ellipsoidal and spherical syntheses is 10-14, 10-12 and 10-8 for the potential and its first and second derivatives, respectively. Using the original renormalization, this agreement is 10-12, 10-8 and 10-5, respectively. In addition, our optimized recurrences require less computation time as the number of required terms for the hypergeometric functions is less. Numéro de notice : A2012-468 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0549-4 Date de publication en ligne : 07/03/2012 En ligne : https://doi.org/10.1007/s00190-012-0549-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31914
in Journal of geodesy > vol 86 n° 9 (September 2012) . - pp 713 - 726[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2012091 RAB Revue Centre de documentation En réserve L003 Disponible Reducing errors in the GRACE gravity solutions using regularization / H. Save in Journal of geodesy, vol 86 n° 9 (September 2012)
[article]
Titre : Reducing errors in the GRACE gravity solutions using regularization Type de document : Article/Communication Auteurs : H. Save, Auteur ; S. Bettadpur, Auteur ; B. Tapley, Auteur Année de publication : 2012 Article en page(s) : pp 695 - 711 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] données GRACE
[Termes IGN] gravimétrie
[Termes IGN] harmonique sphérique
[Termes IGN] levé gravimétrique
[Termes IGN] régularisation de TychonoffRésumé : (Auteur) The nature of the gravity field inverse problem amplifies the noise in the GRACE data, which creeps into the mid and high degree and order harmonic coefficients of the Earth’s monthly gravity fields provided by GRACE. Due to the use of imperfect background models and data noise, these errors are manifested as north-south striping in the monthly global maps of equivalent water heights. In order to reduce these errors, this study investigates the use of the L-curve method with Tikhonov regularization. L-curve is a popular aid for determining a suitable value of the regularization parameter when solving linear discrete ill-posed problems using Tikhonov regularization. However, the computational effort required to determine the L-curve is prohibitively high for a large-scale problem like GRACE. This study implements a parameter-choice method, using Lanczos bidiagonalization which is a computationally inexpensive approximation to L-curve. Lanczos bidiagonalization is implemented with orthogonal transformation in a parallel computing environment and projects a large estimation problem on a problem of the size of about 2 orders of magnitude smaller for computing the regularization parameter. Errors in the GRACE solution time series have certain characteristics that vary depending on the ground track coverage of the solutions. These errors increase with increasing degree and order. In addition, certain resonant and near-resonant harmonic coefficients have higher errors as compared with the other coefficients. Using the knowledge of these characteristics, this study designs a regularization matrix that provides a constraint on the geopotential coefficients as a function of its degree and order. This regularization matrix is then used to compute the appropriate regularization parameter for each monthly solution. A 7-year time-series of the candidate regularized solutions (Mar 2003–Feb 2010) show markedly reduced error stripes compared with the unconstrained GRACE release 4 solutions (RL04) from the Center for Space Research (CSR). Post-fit residual analysis shows that the regularized solutions fit the data to within the noise level of GRACE. A time series of filtered hydrological model is used to confirm that signal attenuation for basins in the Total Runoff Integrating Pathways (TRIP) database over 320 km radii is less than 1 cm equivalent water height RMS, which is within the noise level of GRACE. Numéro de notice : A2012-467 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0548-5 Date de publication en ligne : 10/03/2012 En ligne : https://doi.org/10.1007/s00190-012-0548-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31913
in Journal of geodesy > vol 86 n° 9 (September 2012) . - pp 695 - 711[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2012091 RAB Revue Centre de documentation En réserve L003 Disponible Monitoring GOCE gradiometer calibration parameters using accelerometer and star sensor data: methodology and first results / C. Siemes in Journal of geodesy, vol 86 n° 8 (August 2012)
[article]
Titre : Monitoring GOCE gradiometer calibration parameters using accelerometer and star sensor data: methodology and first results Type de document : Article/Communication Auteurs : C. Siemes, Auteur ; Roger Haagmans, Auteur ; M. Kern, Auteur ; et al., Auteur Année de publication : 2012 Article en page(s) : pp 629 - 645 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] données GOCE
[Termes IGN] étalonnage d'instrument
[Termes IGN] GOCE
[Termes IGN] gradient de gravitation
[Termes IGN] gradiomètre
[Termes IGN] série temporelleRésumé : (Auteur) The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, launched on 17 March 2009, is designed to measure the Earth’s mean gravity field with unprecedented accuracy at spatial resolutions down to 100 km. The accurate calibration of the gravity gradiometer on-board GOCE is of utmost importance for achieving the mission goals. ESA’s baseline method for the calibration uses star sensor and accelerometer data of a dedicated calibration procedure, which is executed every 2 months. In this paper, we describe a method for monitoring the evolution of calibration parameter during that time. The method works with star sensor and accelerometer data and does not require gravity field models, which distinguishes it from other existing methods. We present time series of calibration parameters estimated from GOCE data from 1 November 2009 to 17 May 2010. The time series confirm drifts in the calibration parameters that are present in the results of other methods, including ESA’s baseline method. Although these drifts are very small, they degrade the gravity gradients, leading to the conclusion that the calibration parameters of the ESA’s baseline method need to be linearly interpolated. Further, we find a correction of -36 * 10-6 for one calibration parameter (in-line differential scale factor of the cross-track gradiometer arm), which improves the gravity gradient performance. The results are validated by investigating the trace of the calibrated gravity gradients and comparing calibrated gravity gradients with reference gradients computed along the GOCE orbit using the ITG-Grace-2010s gravity field model. Numéro de notice : A2012-376 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0545-8 Date de publication en ligne : 22/02/2012 En ligne : https://doi.org/10.1007/s00190-012-0545-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31822
in Journal of geodesy > vol 86 n° 8 (August 2012) . - pp 629 - 645[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2012081 RAB Revue Centre de documentation En réserve L003 Disponible Optimal regularization for geopotential model GOCO02S by Monte Carlo methods and multi-scale representation of density anomalies / Karl Rudolf Koch in Journal of geodesy, vol 86 n° 8 (August 2012)PermalinkThe spherical Slepian basis as a means to obtain spectral consistency between mean sea level and the geoid / D. Slobbe in Journal of geodesy, vol 86 n° 8 (August 2012)PermalinkBasic equations for constructing geopotential models from the gravitational potential derivatives of the first and second orders in the terrestrial reference frame / M. Petrovskaya in Journal of geodesy, vol 86 n° 7 (July 2012)PermalinkSeparation of global time-variable gravity signals into maximally independent components / E. Forootan in Journal of geodesy, vol 86 n° 7 (July 2012)Permalink"Yu laid out the lands": georeferencing the Chinese Yujitu (Map of the Tracks of Yu) of 1136 / A. Akin in Cartography and Geographic Information Science, vol 39 n° 3 (July 2012)PermalinkAnalysis of 4 years (2002-2005) of laser data on Starlette, Stella and LAGEOS-1/2 satellites for stations coordinates and Earth orientations parameters (EOP) / Bachir Gourine in Bulletin des sciences géographiques, n° 27 (juin 2012)PermalinkAssessment of the GOCE-based global gravity models in Canada / Elmas Sinem Ince in Geomatica, vol 66 n° 2 (June 2012)PermalinkChoix d'un modèle géopotentiel global pour la détermination du géoïde en Algérie / N. Rabehi in Bulletin des sciences géographiques, n° 27 (juin 2012)PermalinkEinsatz der Atominterferometrie in der Geodäsie / M. Schilling in ZFV, Zeitschrift für Geodäsie, Geoinformation und Landmanagement, vol 137 n° 3 (01/06/2012)PermalinkEstimation of the zero-height geopotential level WoLVD in a local vertical datum from inversion of co-located GPS, leveling and geoid heights: a case study in the Hellenic islands / Christopher Kotsakis in Journal of geodesy, vol 86 n° 6 (June 2012)Permalink