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Hydrological deformation induced by the West African Monsoon : Comparison of GPS, GRACE and loading models / Samuel Nahmani in Journal of geophysical research : Solid Earth, Vol 117 n° B5 (May 2012)
[article]
Titre : Hydrological deformation induced by the West African Monsoon : Comparison of GPS, GRACE and loading models Type de document : Article/Communication Auteurs : Samuel Nahmani , Auteur ; Olivier Bock , Auteur ; Marie-Noëlle Bouin , Auteur ; Alvaro Santamaria Gomez, Auteur ; Jean-Paul Boy, Auteur ; Xavier Collilieux , Auteur ; Laurent Métivier , Auteur ; Isabelle Panet , Auteur ; Pierre Genthon, Auteur ; Caroline de Linage, Auteur ; Guy Wöppelmann , Auteur Année de publication : 2012 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] coordonnées GPS
[Termes IGN] déformation de la croute terrestre
[Termes IGN] données GRACE
[Termes IGN] données météorologiques
[Termes IGN] effet de charge
[Termes IGN] Gao
[Termes IGN] mousson
[Termes IGN] Niamey (Niger)
[Termes IGN] oscillation
[Termes IGN] Ouagadougou
[Termes IGN] station permanente
[Termes IGN] Tombouctou
[Termes IGN] variation saisonnièreRésumé : (Auteur) Three‐dimensional ground deformation measured with permanent GPS stations in West Africa was used for investigating the hydrological loading deformation associated with Monsoon precipitation. The GPS data were processed within a global network for the 2003–2008 period. Weekly station positions were retrieved with a repeatability (including unmodeled loading effects) of 1–2 mm in the horizontal components and between 2.5 and 6 mm in the vertical component. The annual signal in the vertical component for sites located between 9.6°N and 16.7°N is in the range 10–15 mm. It is consistent at the 3 mm‐level with the annual regional‐scale loading deformations estimated from GRACE satellite products and modeled with a combination of hydrological, atmospheric, and nontidal oceanic models. An additional 6 month transient signal was detected in the vertical component of GPS estimates at most of the West African sites. It takes the form of an oscillation occurring between September and March, and reaching a maximum amplitude of 12–16 mm at Ouagadougou (12.5°N). The analysis of in situ hydro‐geological data revealed a strong coincidence between this transient signal and peak river discharge at three sites located along the Niger River (Timbuktu, Gao, and Niamey). At Ouagadougou, a similar coincidence was found with the seasonal variations of the water table depth. We propose a mechanism to account for this signal that involves a sequence of swelling/shrinking of clays combined with local loading effects associated with flooding of the Niger River. Numéro de notice : A2012-753 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2011JB009102 Date de publication en ligne : 12/05/2012 En ligne : https://doi.org/10.1029/2011JB009102 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91470
in Journal of geophysical research : Solid Earth > Vol 117 n° B5 (May 2012)[article]Simulation study of a follow-on gravity mission to GRACE / B. Loomis in Journal of geodesy, vol 86 n° 5 (May 2012)
[article]
Titre : Simulation study of a follow-on gravity mission to GRACE Type de document : Article/Communication Auteurs : B. Loomis, Auteur ; R. Nerem, Auteur ; Scott B. Luthcke, Auteur Année de publication : 2012 Article en page(s) : pp 319 - 335 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] crénelage
[Termes IGN] données GRACE
[Termes IGN] masse de la Terre
[Termes IGN] simulationRésumé : (Auteur) The gravity recovery and climate experiment (GRACE) has been providing monthly estimates of the Earth’s time-variable gravity field since its launch in March 2002. The GRACE gravity estimates are used to study temporal mass variations on global and regional scales, which are largely caused by a redistribution of water mass in the Earth system. The accuracy of the GRACE gravity fields are primarily limited by the satellite-to-satellite range-rate measurement noise, accelerometer errors, attitude errors, orbit errors, and temporal aliasing caused by un-modeled high-frequency variations in the gravity signal. Recent work by Ball Aerospace & Technologies Corp., Boulder, CO has resulted in the successful development of an interferometric laser ranging system to specifically address the limitations of the K-band microwave ranging system that provides the satellite-to-satellite measurements for the GRACE mission. Full numerical simulations are performed for several possible configurations of a GRACE Follow-On (GFO) mission to determine if a future satellite gravity recovery mission equipped with a laser ranging system will provide better estimates of time-variable gravity, thus benefiting many areas of Earth systems research. The laser ranging system improves the range-rate measurement precision to ~0.6 nm/s as compared to ~0.2 ?m/s for the GRACE K-band microwave ranging instrument. Four different mission scenarios are simulated to investigate the effect of the better instrument at two different altitudes. The first pair of simulated missions is flown at GRACE altitude (~480 km) assuming on-board accelerometers with the same noise characteristics as those currently used for GRACE. The second pair of missions is flown at an altitude of ~250 km which requires a drag-free system to prevent satellite re-entry. In addition to allowing a lower satellite altitude, the drag-free system also reduces the errors associated with the accelerometer. All simulated mission scenarios assume a two satellite co-orbiting pair similar to GRACE in a near-polar, near-circular orbit. A method for local time variable gravity recovery through mass concentration blocks (mascons) is used to form simulated gravity estimates for Greenland and the Amazon region for three GFO configurations and GRACE. Simulation results show that the increased precision of the laser does not improve gravity estimation when flown with on-board accelerometers at the same altitude and spacecraft separation as GRACE, even when time-varying background models are not included. This study also shows that only modest improvement is realized for the best-case scenario (laser, low-altitude, drag-free) as compared to GRACE due to temporal aliasing errors. These errors are caused by high-frequency variations in the hydrology signal and imperfections in the atmospheric, oceanographic, and tidal models which are used to remove unwanted signal. This work concludes that applying the updated technologies alone will not immediately advance the accuracy of the gravity estimates. If the scientific objectives of a GFO mission require more accurate gravity estimates, then future work should focus on improvements in the geophysical models, and ways in which the mission design or data processing could reduce the effects of temporal aliasing. Numéro de notice : A2012-241 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-011-0521-8 Date de publication en ligne : 28/10/2011 En ligne : https://doi.org/10.1007/s00190-011-0521-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31687
in Journal of geodesy > vol 86 n° 5 (May 2012) . - pp 319 - 335[article]Réservation
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Titre : Analysis of GRACE gravity field solution release 5 from EIGEN Type de document : Mémoire Auteurs : Jean-Benoit Tranchant, Auteur Editeur : Champs-sur-Marne : Ecole nationale des sciences géographiques ENSG Année de publication : 2012 Importance : 45 p. Format : 21 x 30 cm Note générale : Bibliographie
Project report 2nd year engineer internship, cycle engineerLangues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] données GRACE
[Termes IGN] European Improved Gravity Model of the Earth by New techniques
[Termes IGN] matrice
[Termes IGN] pondérationIndex. décimale : PROJET Mémoires : Rapports de projet - stage des ingénieurs de 2e année Résumé : (Auteur) Les solutions mensuelles du champ de pesanteur fournies par la mission GRACE sont une source importante d'analyse géophysique du champ terrestre (hydrologie, fonte des glaces...) depuis maintenant 10 ans. A cette occasion, une nouvelle solution mensuelle, la release 5, RL05, a été produite. Elle sera ici comparée à sa version précédente la release 4, RL04, afin d'étudier le gain de précision apporté. Seule la solution calculée à partir des données GRACE de l'institut EIGEN est utilisée ici. Dans ce rapport, la nouvelle précision des données apportée par la release 5 par rapport à la release 4 sur la période 2005-2010 sera étudiée afin d'en mesurer précisément l'impact sur la modélisation des phénomènes suivants : la modélisation et les différences entre les géoïdes calculés par les 2 releases, l'évolution des erreurs et les mouvements de masse dans le bassin Amazonien et au Groenland. L'amélioration apportée par la release 5 est de l'ordre d'un facteur 2,1 sur la déviation des coefficients de Stockes, autrement dit le bruit autour du signal réel. L'erreur moyenne sur les coefficients donnée par le modèle a également diminué d'un facteur 2,9. Note de contenu : 1- Introduction
2- Data
2.1- Release 4
2.2- Release 5
2.3- Improvements
2.4- Construction of the data
3- Analysis
3.1- Global Analysis
3.1.1- Process
3.1.2- Results
3.2- Earth Mass Variation
3.2.1- Process
3.2.2- Weight Matrix
3.2.3- Overall pattern
3.2.4- Results
3.3- Estimation of the method
3.3.1- Aim and Process
3.3.2- Results
4- ConclusionNuméro de notice : 14540 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Mémoire de projet pluridisciplinaire Organisme de stage : Institut fur Astronomische und Physikalische Geodasie München Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=50495 Réservation
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14540_mem_pp_2012_rapport_grace_4.5_tranchant.pdfAdobe Acrobat PDF Entwicklung eines Kalman-Filters zur Bestimmung kurzzeitiger Variationen des Erdschwerefeldes aus daten der Satellitenmission GRACE / E. Kurtenbach (2012)
Titre : Entwicklung eines Kalman-Filters zur Bestimmung kurzzeitiger Variationen des Erdschwerefeldes aus daten der Satellitenmission GRACE Titre original : Development of a Kalman filter to derive short-term variations of the Earth's gravity field from GRACE data Type de document : Thèse/HDR Auteurs : E. Kurtenbach, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 2012 Collection : DGK - C Sous-collection : Dissertationen num. 683 Importance : 120 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-7696-5095-2 Note générale : Bibliographie Langues : Allemand (ger) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] corrélation automatique de points homologues
[Termes IGN] crénelage
[Termes IGN] données GRACE
[Termes IGN] filtre de Kalman
[Termes IGN] série temporelle
[Termes IGN] variation temporelleRésumé : (Auteur) The gravitational field and its temporal variations represent an important observable for the monitoring of the Earth's system. The satellite mission GRACE (Gravity Recovery And Climate Experiment) is, for the first time, able to measure gravity field variations with homogeneous global coverage. Nevertheless, the predicted GRACE accuracy has not been reached yet, partly due to the insufficient representation of the temporal variations in terms of monthly mean fields. In this thesis, an approach is presented which allows the calculation of daily GRACE solutions with the goal of modeling short-term gravity field variations. This time series can on the one hand be used to improve the knowledge of the underlying geophysical processes. On the other hand the daily GRACE solutions can also be used to improve the monthly mean fields. Increasing the temporal resolution is accompanied by a loss of accuracy due to insufficient data coverage. Therefore, additional information in terms of temporal and spatial correlations of the expected gravity signal is introduced into the analysis process. The combination of the GRACE observations and the correlation patterns is then performed within a Kalman filter framework. In a simulation study, the performance of the approach at hand is investigated and, in a second step, applied to real GRACE LIB data. Comparisons to independent data sets, i.e. vertical displacements of GPS stations and ocean bottom pressure time series, reveal that the daily GRACE time series contains geophysically interpretable signal. Furthermore, the daily GRACE time series can be used to significantly reduce the effects of temporal aliasing in the processing of monthly mean gravity field solutions. Numéro de notice : 14619 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62670 Documents numériques
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14619_dgk-c-683_kurtenbach.pdfAdobe Acrobat PDF Méthodologies en traitement de données GPS pour les sciences de l’environnement / Samuel Nahmani (2012)PermalinkValidation of international reference ionosphere models using in situ measurements from GRACE K-band ranging system and CHAMP planar Langmuir probe / C. Lee in Journal of geodesy, vol 85 n° 12 (December 2011)PermalinkMission design, operation and exploitation of the gravity field and steady-state ocean circulation explorer mission / R. Floberghagen in Journal of geodesy, vol 85 n° 11 (November /2011)PermalinkValidation of GOCE gravity field models by means of orbit residuals and geoid comparisons / Thomas Gruber in Journal of geodesy, vol 85 n° 11 (November /2011)PermalinkAlternative method for angular rate determination within the GOCE gradiometer processing / C. Stummer in Journal of geodesy, vol 85 n° 9 (September 2011)PermalinkGRACE-derived surface water mass anomalies by energy integral approach: application to continental hydrology / Guillaume Ramillien in Journal of geodesy, vol 85 n° 6 (June 2011)PermalinkPacific geoid anomalies revisited in light of thermochemical oscillating domes in the lower mantle / Cécilia Cadio in Earth and planetary science letters, vol 306 n° 1-2 (June 2011)PermalinkPermalinkAssessment of systematic errors in the computation of gravity gradients from satellite altimeter data / Johannes Bouman in Marine geodesy, vol 34 n° 2 (April - June 2011)PermalinkEtude géodésique du changement climatique en Méditerranée : première approche / Pierre Valty in Bulletin d'information scientifique et technique de l'IGN, n° 77 (avril 2011)Permalink