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Comparative analysis of different atmospheric surface pressure models and their impacts on daily ITRF2014 GNSS residual time series / Zhao Li in Journal of geodesy, vol 94 n°4 (April 2020)  

Public [article]  inJournal of geodesy > vol 94 n°4 (April 2020) . - n° 42 Titre : Comparative analysis of different atmospheric surface pressure models and their impacts on daily ITRF2014 GNSS residual time series Type de document : Article/Communication Auteurs : Zhao Li, Auteur ; Chen Wu, Auteur ; Tonie M. van Dam, Auteur ; Paul Rebischung , Auteur ; Zuheir Altamimi , Auteur Année de publication : 2020 Projets : 3-projet - voir note / Article en page(s) : n° 42 Note générale : bibliographie This research is supported by the National Key Research and Development Program of China (Project 2016YFB0502101), the European Commission/Research Grants Council (RGC) Collaboration Scheme sponsored by the Research Grants Council of Hong Kong Special Administrative Region, China (Project No. E-PolyU 501/16), and the National Science Foundation for Distinguished Young Scholars of China (Grant No. 41525014). Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] analyse comparative [Termes IGN] coefficient de corrélation [Termes IGN] données GNSS [Termes IGN] International Terrestrial Reference Frame [Termes IGN] MERRA [Termes IGN] modèle atmosphérique [Termes IGN] pression atmosphérique [Termes IGN] radar JPL [Termes IGN] résidu [Termes IGN] série temporelle [Termes IGN] station GNSS Résumé : (auteur) To remove atmospheric pressure loading (ATML) effect from GNSS coordinate time series, surface pressure (SP) models are required to predict the displacements. In this paper, we modeled the 3D ATML surface displacements using the latest MERRA-2 SP grids, together with four other products (NCEP-R-1, NCEP-R-2, ERA-Interim and MERRA) for 596 globally distributed GNSS stations, and compared them with ITRF2014 residual time series. The five sets of ATML displacements are highly consistent with each other, particularly for those stations far away from coasts, of which the lowest correlations in the Up component for all the four models w.r.t MERRA-2 become larger than 0.91. ERA-Interim-derived ATML displacement performs best in reducing scatter of the GNSS height for 90.3% of the stations (89.3% for NCEP-R-1, 89.1% for NCEP-R-2, 86.4% for MERRA and 85.1% for MERRA-2). We think that this may be possibly due to the 4D variational data assimilation method applied. Considering inland stations only, more than 96% exhibit WRMS reduction in the Up direction for all five models, with an average improvement of 3–4% compared with the original ITRF2014 residual time series before ATML correction. Most stations (> 67%) also exhibit horizontal WRMS reductions based on the five models, but of small magnitudes, with most improvements (> 76%) less than 5%. In particular, most stations in South America, South Africa, Oceania and the Southern Oceans show larger WRMS reductions with MERRA-2, while all other four SP datasets lead to larger WRMS reduction for the Up component than MERRA-2 in Europe. Through comparison of the daily pressure variation from the five SP models, we conclude that the bigger model differences in the SP-induced surface displacements and their impacts on the ITRF2014 residuals for coastal/island stations are mainly due to the IB correction based on the different land–sea masks. A unique high spatial resolution land–sea mask should be applied in the future, so that model differences would come from only SP grids. Further research is also required to compare the ATML effect in ice-covered and high mountainous regions, for example the Qinghai–Tibet Plateau in China, the Andes in South America, etc., where larger pressure differences between models tend to occur. Numéro de notice : A2020-159 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01370-y Date de publication en ligne : 20/03/2020 En ligne : https://doi.org/10.1007/s00190-020-01370-y Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94813 [article]

Data-adaptive spatio-temporal filtering of GRACE data / Paoline Prevost in Geophysical journal international, vol 219 n° 3 (December 2019)  

Public [article]  inGeophysical journal international > vol 219 n° 3 (December 2019) . - pp 2034 - 2055 Titre : Data-adaptive spatio-temporal filtering of GRACE data Type de document : Article/Communication Auteurs : Paoline Prevost, Auteur ; Kristel Chanard , Auteur ; Luce Fleitout, Auteur ; Eric Calais, Auteur ; Damian Walwer, Auteur ; Tonie M. van Dam, Auteur ; Michael Ghil, Auteur Année de publication : 2019 Projets : 2-Pas d'info accessible - article non ouvert / Article en page(s) : pp 2034 - 2055 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] analyse de spectre singulier [Termes IGN] données géophysiques [Termes IGN] données GRACE [Termes IGN] filtrage spatiotemporel [Termes IGN] harmonique sphérique Résumé : (auteur) Measurements of the spatio-temporal variations of Earth’s gravity field from the Gravity Recovery and Climate Experiment (GRACE) mission have led to new insights into large spatial mass redistribution at secular, seasonal and subseasonal timescales. GRACE solutions from various processing centres, while adopting different processing strategies, result in rather coherent estimates. However, these solutions also exhibit random as well as systematic errors, with specific spatial patterns in the latter. In order to dampen the noise and enhance the geophysical signals in the GRACE data, we propose an approach based on a data-driven spatio-temporal filter, namely the Multichannel Singular Spectrum Analysis (M-SSA). M-SSA is a data-adaptive, multivariate, and non-parametric method that simultaneously exploits the spatial and temporal correlations of geophysical fields to extract common modes of variability. We perform an M-SSA analysis on 13 yr of GRACE spherical harmonics solutions from five different processing centres in a simultaneous setup. We show that the method allows us to extract common modes of variability between solutions, while removing solution-specific spatio-temporal errors that arise from the processing strategies. In particular, the method efficiently filters out the spurious north–south stripes, which are caused in all likelihood by aliasing, due to the imperfect geophysical correction models and low-frequency noise in measurements. Comparison of the M-SSA GRACE solution with mass concentration (mascons) solutions shows that, while the former remains noisier, it does retrieve geophysical signals masked by the mascons regularization procedure. Numéro de notice : A2019-276 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1093/gji/ggz409 Date de publication en ligne : 19/09/2019 En ligne : https://doi.org/10.1093/gji/ggz409 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95381 [article]

Mass variation observing system by high low inter-satellite links (MOBILE) : a new concept for sustained observation of mass transport from space / Roland Pail in Journal of geodetic science, vol 9 n° 1 (January 2019)  

Public [article]  inJournal of geodetic science > vol 9 n° 1 (January 2019) . - pp 48 - 58 Titre : Mass variation observing system by high low inter-satellite links (MOBILE) : a new concept for sustained observation of mass transport from space Type de document : Article/Communication Auteurs : Roland Pail, Auteur ; Jonathan Bamber, Auteur ; Richard Biancale, Auteur ; Rory Bingham, Auteur ; Carla Braitenberg, Auteur ; Annette Eicker, Auteur ; Frank Flechtner, Auteur ; Thomas Gruber, Auteur ; Andreas Güntner, Auteur ; Gerhard Heinzel, Auteur ; Martin Horwath, Auteur ; Laurent Longuevergne, Auteur ; J. Muller, Auteur ; Isabelle Panet , Auteur ; Hubert Savenije, Auteur ; S. Seneviratne, Auteur ; Nico Sneeuw, Auteur ; Tonie M. van Dam, Auteur ; Bert Wouters, Auteur Année de publication : 2019 Projets : 1-Pas de projet / Article en page(s) : pp 48 - 58 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] gravimétrie spatiale [Termes IGN] harmonique sphérique [Termes IGN] masse Résumé : (auteur) As changes in gravity are directly related to mass variability, satellite missions observing the Earth’s time varying gravity field are a unique tool for observing mass transport processes in the Earth system, such as the water cycle, rapid changes in the cryosphere, oceans, and solid Earth processes, on a global scale. The observation of Earth’s gravity field was successfully performed by the GRACE and GOCE satellite missions, and will be continued by the GRACE Follow-On mission. A comprehensive team of European scientists proposed the next-generation gravity field mission MOBILE in response to the European Space Agency (ESA) call for a Core Mission in the frame of Earth Explorer 10 (EE10). MOBILE is based on the innovative observational concept of a high-low tracking formation with micrometer ranging accuracy, complemented by new instrument concepts. Since a high-low tracking mission primarily observes the radial component of gravity-induced orbit perturbations, the error structure is close to isotropic. This geometry significantly reduces artefacts of previous along-track ranging low-low formations (GRACE, GRACE-Follow-On) such as the typical striping patterns. The minimum configuration consists of at least two medium-Earth orbiters (MEOs) at 10000 km altitude or higher, and one low-Earth orbiter (LEO) at 350-400 km. The main instrument is a laser-based distance or distance change measurement system, which is placed at the LEO. The MEOs are equipped either with passive reflectors or transponders. In a numerical closed-loop simulation, it was demonstrated that this minimum configuration is in agreement with the threshold science requirements of 5 mm equivalent water height (EWH) accuracy at 400 km wavelength, and 10 cm EWH at 200 km. MOBILE provides promising potential future perspectives by linking the concept to existing space infrastructure such as Galileo next-generation, as future element of the Copernicus/Sentinel programme, and holds the potential of miniaturization even up to swarm configurations. As such MOBILE can be considered as a precursor and role model for a sustained mass transport observing system from space. Numéro de notice : A2019-635 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1515/jogs-2019-0006 Date de publication en ligne : 21/10/2019 En ligne : https://doi.org/10.1515/jogs-2019-0006 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95454 [article]

Seasonal low-degree changes in terrestrial water mass load from global GNSS measurements / Thierry Meyrath in Journal of geodesy, vol 91 n° 11 (November 2017)  

Public [article]  inJournal of geodesy > vol 91 n° 11 (November 2017) . - pp 1 - 22 Titre : Seasonal low-degree changes in terrestrial water mass load from global GNSS measurements Type de document : Article/Communication Auteurs : Thierry Meyrath, Auteur ; Tonie M. van Dam, Auteur ; Xavier Collilieux , Auteur ; Paul Rebischung , Auteur Année de publication : 2017 Projets : 1-Pas de projet / Article en page(s) : pp 1 - 22 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] coordonnées GNSS [Termes IGN] géocentre [Termes IGN] masse d'eau [Termes IGN] mouvement du géocentre [Termes IGN] surcharge océanique [Termes IGN] variation saisonnière Résumé : (auteur) Large-scale mass redistribution in the terrestrial water storage (TWS) leads to changes in the low-degree spherical harmonic coefficients of the Earth’s surface mass density field. Studying these low-degree fluctuations is an important task that contributes to our understanding of continental hydrology. In this study, we use global GNSS measurements of vertical and horizontal crustal displacements that we correct for atmospheric and oceanic effects, and use a set of modified basis functions similar to Clarke et al. (Geophys J Int 171:1–10, 2007) to perform an inversion of the corrected measurements in order to recover changes in the coefficients of degree-0 (hydrological mass change), degree-1 (centre of mass shift) and degree-2 (flattening of the Earth) caused by variations in the TWS over the period January 2003–January 2015. We infer from the GNSS-derived degree-0 estimate an annual variation in total continental water mass with an amplitude of (3.49±0.19)×103 Gt and a phase of 70∘±3∘ (implying a peak in early March), in excellent agreement with corresponding values derived from the Global Land Data Assimilation System (GLDAS) water storage model that amount to (3.39±0.10)×103 Gt and 71∘±2∘, respectively. The degree-1 coefficients we recover from GNSS predict annual geocentre motion (i.e. the offset change between the centre of common mass and the centre of figure) caused by changes in TWS with amplitudes of 0.69±0.07 mm for GX, 1.31±0.08 mm for GY and 2.60±0.13 mm for GZ. These values agree with GLDAS and estimates obtained from the combination of GRACE and the output of an ocean model using the approach of Swenson et al. (J Geophys Res 113(B8), 2008) at the level of about 0.5, 0.3 and 0.9 mm for GX, GY and GZ, respectively. Corresponding degree-1 coefficients from SLR, however, generally show higher variability and predict larger amplitudes for GX and GZ. The results we obtain for the degree-2 coefficients from GNSS are slightly mixed, and the level of agreement with the other sources heavily depends on the individual coefficient being investigated. The best agreement is observed for TC20 and TS22, which contain the most prominent annual signals among the degree-2 coefficients, with amplitudes amounting to (5.47±0.44)×10−3 and (4.52±0.31)×10−3 m of equivalent water height (EWH), respectively, as inferred from GNSS. Corresponding agreement with values from SLR and GRACE is at the level of or better than 0.4×10−3 and 0.9×10−3 m of EWH for TC20 and TS22, respectively, while for both coefficients, GLDAS predicts smaller amplitudes. Somewhat lower agreement is obtained for the order-1 coefficients, TC21 and TS21, while our GNSS inversion seems unable to reliably recover TC22. For all the coefficients we consider, the GNSS-derived estimates from the modified inversion approach are more consistent with the solutions from the other sources than corresponding estimates obtained from an unconstrained standard inversion. Numéro de notice : A2017-311 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-017-1028-8 Date de publication en ligne : 25/04/2017 En ligne : http://doi.org/10.1007/s00190-017-1028-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85361 [article]

Statistical comparison and combination of GPS, GLONASS, and multi-GNSS multipath reflectometry applied to snow depth retrieval / Sajad Tabibi in IEEE Transactions on geoscience and remote sensing, vol 55 n° 7 (July 2017)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 55 n° 7 (July 2017) . - pp 3773 - 3785 Titre : Statistical comparison and combination of GPS, GLONASS, and multi-GNSS multipath reflectometry applied to snow depth retrieval Type de document : Article/Communication Auteurs : Sajad Tabibi, Auteur ; Felipe Geremia-Nievinski, Auteur ; Tonie M. van Dam, Auteur Année de publication : 2017 Article en page(s) : pp 3773 - 3785 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] épaisseur [Termes IGN] neige [Termes IGN] positionnement par GLONASS [Termes IGN] positionnement par GNSS [Termes IGN] positionnement par GPS [Termes IGN] réflectométrie par GNSS [Termes IGN] série temporelle Résumé : (Auteur) Global navigation satellite system (GNSS) multipath reflectometry (MR) has emerged as a new technique that uses signals of opportunity broadcast by GNSS satellites and tracked by ground-based receivers to retrieve environmental variables such as snow depth. The technique is based on the simultaneous reception of direct or line-of-sight (LOS) transmissions and corresponding coherent surface reflections (non-LOS). Until recently, snow depth retrieval algorithms only used legacy and modernized GPS signals. Using multiple GNSS constellations for reflectometry would improve GNSS-MR applications by providing more observations from more satellites and independent signals (carrier frequencies and code modulations). We assess GPS and GLONASS for combined multi-GNSS-MR using simulations as well as field measurements. Synthetic observations for different signals indicated a lack of detectable interfrequency and intercode biases in GNSS-MR snow depth retrievals. Received signals from a GNSS station continuously operating in France for a two-winter period are used for experimental snow depth retrieval. We perform an internal validation of various GNSS signals against the proven GPS-L2-C signal, which was validated externally against in situ snow depth in previous studies. GLONASS observations required a more complex handling to account for topography because of its particular ground track repeatability. Signal intercomparison show an average correlation of 0.922 between different GPS snow depths and GPS-L2-CL, while GLONASS snow depth retrievals have an average correlation that exceeds 0.981. In terms of precision and accuracy, legacy GPS signals are worse, while GLONASS signals and modernized GPS signals are of comparable quality. Finally, we show how an optimal multi-GNSS combined daily snow depth time series can be formed employing variance factors with a ~59%-90% precision improvement compared to individual signal snow depth retrievals, resulting in snow depth retrieval with uncertainty of 1.3 cm. The developed combination strategy can also be applied for the European Galileo and the Chines BeiDou navigation systems. Numéro de notice : A2017-487 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2017.2679899 En ligne : http://dx.doi.org/10.1109/TGRS.2017.2679899 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86414 [article]

GRACE era variability in the Earth's oblateness: a comparison of estimates from six different sources / Thierry Meyrath in Geophysical journal international, vol 208 n° 2 (February 2017)  

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Quality evaluation of the weekly vertical loading effects induced from continental water storage models / Z. Li (2016)  

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Singular spectrum analysis for modeling seasonal signals from GPS time series / Q. Chen in Journal of geodynamics, vol 72 (December 2013)  

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Earth System Mass Transport Mission (e.motion): A Concept for Future Earth Gravity Field Measurements from Space / Isabelle Panet in Surveys in Geophysics, vol 34 n° 2 (March 2013)  

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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)  

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The effect of using inconsistent ocean tidal loading models on GPS coordinate solutions / Y. Fu in Journal of geodesy, vol 86 n° 6 (June 2012)  

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Strategies to mitigate aliasing of loading signals while estimating GPS frame parameters / Xavier Collilieux in Journal of geodesy, vol 86 n° 1 (January 2012)  

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Correction to “Topographically induced height errors in predicted atmospheric loading effects” / Tonie M. van Dam in Journal of geophysical research : Solid Earth, Vol 116 n° B11 (November 2011)  

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Quality assessment of GPS reprocessed terrestrial reference frame / Xavier Collilieux in GPS solutions, vol 15 n° 3 (July 2011)  

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Improved constraints on models of glacial isostatic adjustment: A review of the contribution of ground-based geodetic observations / Matt A. King in Surveys in Geophysics, vol 31 n° 5 (September 2010)    

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