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Auteur Samuel Nahmani
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chercheur dans l'axe de recherche Géodésie et atmosphère, au Lareg devenu équipe géodésie dans l'UMR IPGP
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GRGS numerical simulations for a GRASP-like mission: A way to reach the GGOS goal for terrestrial reference frame / Arnaud Pollet in Journal of geodesy, vol 97 n° 5 (May 2023)
[article]
Titre : GRGS numerical simulations for a GRASP-like mission: A way to reach the GGOS goal for terrestrial reference frame Type de document : Article/Communication Auteurs : Arnaud Pollet , Auteur ; David Coulot , Auteur ; Richard Biancale, Auteur ; Felix Perozans, Auteur ; Sylvain Loyer, Auteur ; J.C. Marty, Auteur ; Susanne Glaser, Auteur ; Vladimir Schott-Guilmault, Auteur ; Jean-Michel Lemoine, Auteur ; Flavien Mercier, Auteur ; Samuel Nahmani , Auteur ; Mioara Mandea, Auteur Année de publication : 2023 Article en page(s) : n° 45 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] International DORIS Service
[Termes IGN] mission spatiale
[Termes IGN] orbitographie
[Termes IGN] positionnement par ITGB
[Termes IGN] positionnement par télémétrie laser sur satellite
[Termes IGN] repère de référenceRésumé : (auteur) In 2009, the geoscience community has fixed an objective of 1 mm accuracy and 0.1 mm/yr stability for the terrestrial reference frame (TRF) realization (Global Geodetic Observing System, GGOS, Meeting the Requirements of a Global Society on a Changing Planet in 2020, Plag and Pearlman in Global geodetic observing system: meeting the requirements of a global society on a changing planet in 2020. Springer, Berlin, 2009. https://doi.org/10.1007/978-3-642-02687-4). This accuracy and stability are needed for diversified studies like climate change, tectonic sciences and more generally any geoscience requiring the use of an accurate and precise TRF. Unfortunately, they are still not reached by the last International Terrestrial Reference Frame. To reach this goal, the use of “multi-technique” satellites as “space-ties” has been studied since 2011 and a few proposals have been made in response to different space agency calls: the Geodetic Reference Antenna in Space (GRASP) mission—NASA Earth Venture 2 call, Eratosthenes-GRASP (E-GRASP)—ESA Earth Explorer 9 (EE9) call, MOBILE—ESA EE10 call, MARVEL—CNES Séminaire de Prospective Scientifique 2019). In this article, we present the numerical simulations carried out by the French Groupe de Recherche de Géodésie Spatiale (GRGS) for the E-GRASP proposal in response to the ESA EE-9 call and their improvements carried out afterwards. These simulations aim to answer three different questions:
Is it possible to reach the GGOS requirements for the TRF with the measurements of a GRASP-like satellite like E-GRASP alone?
If it is possible, which level of accuracy for the positioning of the on-board antennas is needed?
What is the minimal lifetime of a E-GRASP mission to reach the GGOS requirements?
The results of these simulations show that a E-GRASP satellite can allow us to reach, after five years, an accuracy close to 1 mm and a stability better than 0.1 mm/yr for the TRF. However, it is necessary to ensure a positioning better than 1 mm for the on-board antennas. We therefore encourage the new ESA GENESIS mission proposal, accepted during the ESA last Ministerial meeting on 23rd November 2022, which takes up the concept of a GRASP-type satellite.Numéro de notice : A2023-227 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-023-01730-4 Date de publication en ligne : 15/05/2023 En ligne : https://doi.org/10.1007/s00190-023-01730-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=103247
in Journal of geodesy > vol 97 n° 5 (May 2023) . - n° 45[article]Advanced GNSS tropospheric products for monitoring severe weather events and climate, ch. 5. Use of GNSS Tropospheric Products for Climate Monitoring (Working Group 3) / Olivier Bock (2020)
contenu dans Advanced GNSS tropospheric products for monitoring severe weather events and climate / Jonathan Jones (2020)
Titre de série : Advanced GNSS tropospheric products for monitoring severe weather events and climate, ch. 5 Titre : Use of GNSS Tropospheric Products for Climate Monitoring (Working Group 3) Type de document : Chapitre/Contribution Auteurs : Olivier Bock , Auteur ; Rosa Pacione, Auteur ; F. Ahmed, Auteur ; A. Araszkiewicz, Auteur ; et al., Auteur ; Samuel Nahmani , Auteur ; Paul Rebischung , Auteur ; Pascal Willis , Auteur Editeur : Berlin, Heidelberg, Vienne, New York, ... : Springer Année de publication : 2020 Projets : GNSS4SWEC / Importance : pp 267 - 402 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] données GNSS
[Termes IGN] format SINEX
[Termes IGN] propagation troposphérique
[Termes IGN] retard troposphérique zénithal
[Termes IGN] série temporelle
[Termes IGN] surveillance météorologique
[Termes IGN] teneur intégrée en vapeur d'eauRésumé : (Auteur) There has been growing interest in recent years in the use of homogeneously reprocessed ground-based GNSS, VLBI, and DORIS measurements for climate applications. Existing datasets are reviewed and the sensitivity of tropospheric estimates to the processing details is discussed. The uncertainty in the derived IWV estimates and linear trends is around 1 kg m−2 RMS and ± 0.3 kg m−2 per decade, respectively. Standardized methods for ZTD outlier detection and IWV conversion are proposed. The homogeneity of final time series is limited however by changes in the stations equipment and environment. Various homogenization algorithms have been evaluated based on a synthetic benchmark dataset. The uncertainty of trends estimated from the homogenized times series is estimated to ±0.5 kg m−2 per decade. Reprocessed GNSS IWV data are analysed along with satellites data, reanalyses and global and regional climate model simulations. A selection of global and regional reprocessed GNSS datasets and ERA-interim reanalysis are made available through the GOP-TropDB tropospheric database and online service. A new tropo SINEX format, providing new features and simplifications, was developed and it is going to be adopted by all the IAG services. Numéro de notice : H2020-001 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Chapître / contribution nature-HAL : ChOuvrScient DOI : 10.1007/978-3-030-13901-8_5 Date de publication en ligne : 14/09/2019 En ligne : https://doi.org/10.1007/978-3-030-13901-8_5 Format de la ressource électronique : URL chapitre Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94504 Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa / Samuel Nahmani in Atmospheric chemistry and physics, vol 19 n° 14 (July 2019)
[article]
Titre : Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa Type de document : Article/Communication Auteurs : Samuel Nahmani , Auteur ; Olivier Bock , Auteur ; Françoise Guichard, Auteur Année de publication : 2019 Projets : VEGAN / Bock, Olivier, TOSCA / Bock, Olivier Article en page(s) : pp 9541 - 9561 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] analyse de sensibilité
[Termes IGN] bande C
[Termes IGN] convection
[Termes IGN] données GPS
[Termes IGN] GAMIT
[Termes IGN] GIPSY-OASIS
[Termes IGN] gradient de troposphère
[Termes IGN] meso échelle
[Termes IGN] modèle atmosphérique
[Termes IGN] Niger
[Termes IGN] propagation troposphérique
[Termes IGN] résidu
[Termes IGN] retard troposphérique zénithal
[Termes IGN] signal GPSRésumé : (Auteur) This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a 3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS software packages, were analyzed and intercompared. First, the case of a MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. However, the sensitivity is different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of ZWDs and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for ZWDs and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station. Numéro de notice : A2019-572 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/acp-19-9541-2019 Date de publication en ligne : 29/07/2019 En ligne : https://doi.org/10.5194/acp-19-9541-2019 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94444
in Atmospheric chemistry and physics > vol 19 n° 14 (July 2019) . - pp 9541 - 9561[article]Quality evaluation of the weekly vertical loading effects induced from continental water storage models / Z. Li (2016)
Titre : Quality evaluation of the weekly vertical loading effects induced from continental water storage models Type de document : Article/Communication Auteurs : Z. Li, Auteur ; Tonie M. van Dam, Auteur ; Xavier Collilieux , Auteur ; Zuheir Altamimi , Auteur ; Paul Rebischung , Auteur ; Samuel Nahmani , Auteur Editeur : Berlin, Heidelberg, Vienne, New York, ... : Springer Année de publication : 2016 Collection : International Association of Geodesy Symposia, ISSN 0939-9585 num. 143 Conférence : IAG 2013, Scientific assembly, IAG 150 Years Postdam Allemagne Proceedings Springer Importance : pp 45 - 54 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Amérique du nord
[Termes IGN] coordonnées GPS
[Termes IGN] eaux continentales
[Termes IGN] effet de charge
[Termes IGN] hauteur ellipsoïdale
[Termes IGN] série temporelleRésumé : (auteur) To remove continental water storage (CWS) signals from the GPS data, CWS mass models are needed to obtain predicted surface displacements. We compared weekly GPS height time series with five CWS models: (1) the monthly and (2) three-hourly Global Land Data Assimilation System (GLDAS); (3) the monthly and (4) one-hourly Modern-Era Retrospective Analysis for Research and Applications (MERRA); (5) the six-hourly National Centers for Environmental Prediction-Department of Energy (NCEP-DOE) global reanalysis products (NCEP-R-2). We find that of the 344 selected global IGS stations, more than 77% of stations have their weighted root mean square (WRMS) reduced in the weekly GPS height by using both the GLDAS and MERRA CWS products to model the surface displacement, and the best improvement concentrate mainly in North America and Eurasia. We find that the one-hourly MERRA-Land dataset is the most appropriate product for modeling weekly vertical surface displacement caused by CWS variations. The three-hourly GLDAS data ranks the second, while the GLDAS and MERRA monthly products rank the third. The higher spatial resolution MERRA product improves the performance of the CWS model in reducing the scatter of the GPS height by about 2–6% compared with the GLDAS. Under the same spatial resolution, the higher temporal resolution could also improve the performance by almost the same magnitude. We also confirm that removing the ATML and NTOL effects from the weekly GPS height would remarkably improve the performance of CWS model in correcting the GPS height by at least 10%, especially for coastal and island stations. Since the GLDAS product has a much greater latency than the MERRA product, MERRA would be a better choice to model surface displacements from CWS. Finally, we find that the NCEP-R-2 data is not sufficiently precise to be used for this application. Further work is still required to determine the reason. Numéro de notice : C2013-011 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : 10.1007/1345_2015_174 Date de publication en ligne : 30/07/2015 En ligne : https://doi.org/10.1007/1345_2015_174 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91895 Comparison of individual and combined zenith tropospheric delay estimations during CONT08 campaign / Arnaud Pollet in Journal of geodesy, vol 88 n° 11 (November 2014)
[article]
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 zénithalRésumé : (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
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Code-barres Cote Support Localisation Section Disponibilité 266-2014111 SL Revue Centre de documentation Revues en salle Disponible Land water storage changes from ground and space geodesy : first results from the GHYRAF (Gravity and Hydrology in Africa) experiment / Jacques Hinderer in Pure and applied geophysics, vol 169 n° 8 (August 2012)PermalinkHydrological 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)PermalinkMéthodologies en traitement de données GPS pour les sciences de l’environnement / Samuel Nahmani (2012)PermalinkMéthodologie en traitement de données GPS et analyse des retards troposphériques dans le cadre du projet AMMA / Samuel Nahmani in Bulletin d'information scientifique et technique de l'IGN, n° 77 (avril 2011)PermalinkWest African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA) / Olivier Bock in Journal of geophysical research : Atmospheres, vol 113 n° D21 (16 November 2008)PermalinkL'allongement troposphérique / Samuel Nahmani (2008)PermalinkÉtude comparative de différentes méthodes d'estimation / Samuel Nahmani (2008)PermalinkPermalinkCalcul de l'allongement troposphérique via l'utilisation de cartes de l'ECMWF / Samuel Nahmani (2005)Permalink