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Impact of offsets on assessing the low-frequency stochastic properties of geodetic time series / Kevin Gobron in Journal of geodesy, vol 96 n° 7 (July 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 7 (July 2022) . - n° 46 Titre : Impact of offsets on assessing the low-frequency stochastic properties of geodetic time series Type de document : Article/Communication Auteurs : Kevin Gobron, Auteur ; Paul Rebischung , Auteur ; Olivier de Viron, Auteur ; Alain Demoulin, Auteur ; Michel Van Camp, Auteur Année de publication : 2022 Projets : 3-projet - voir note / Article en page(s) : n° 46 Note générale : bibliographie This study has been financially supported by the Direction Générale de l’Armement (DGA), the Nouvelle-Aquitaine region, and the Centre National des Etudes Spatiales (CNES) as an application of the geodesy missions. This research was also supported by the Brain LASUGEO project entitled “monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements” funded by the Belgian Sciences Policy. Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse de variance [Termes IGN] bruit blanc [Termes IGN] fréquence [Termes IGN] méthode du maximum de vraisemblance (estimation) [Termes IGN] modèle de Gauss-Markov [Termes IGN] modèle stochastique [Termes IGN] série temporelle [Termes IGN] vitesse Résumé : (auteur) Understanding and modelling the properties of the stochastic variations in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the increasing span of geodetic time series, it is expected that additional observations would help better understand the low-frequency properties of these stochastic variations. In the meantime, recent studies evidenced that the choice of the functional model for the time series biases the assessment of these low-frequency stochastic properties. In particular, frequent offsets in position time series can hinder the evaluation of the noise level at low frequencies and prevent the detection of possible random-walk-type variability. This study investigates the ability of the Maximum Likelihood Estimation (MLE) method to correctly retrieve low-frequency stochastic properties of geodetic time series in the presence of frequent offsets. We show that part of the influence of offsets reported by previous studies results from the MLE method estimation biases. These biases occur even when all offset epochs are correctly identified and accounted for in the trajectory model. They can cause a dramatic underestimation of deterministic parameter uncertainties. We show that one can avoid biases using the Restricted Maximum Likelihood Estimation (RMLE) method. Yet, even when using the RMLE method or equivalent, adding offsets to the trajectory model inevitably blurs the estimated low-frequency properties of geodetic time series by increasing low-frequency stochastic parameter uncertainties more than other stochastic parameters. Numéro de notice : A2022-519 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-022-01634-9 Date de publication en ligne : 29/06/2022 En ligne : https://doi.org/10.1007/s00190-022-01634-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=101072 [article]

Influence of aperiodic non-tidal atmospheric and oceanic loading deformations on the stochastic properties of global GNSS vertical land motion time series / Kevin Gobron in Journal of geophysical research : Solid Earth, vol 126 n° 9 (September 2021)  

Public [article]  inJournal of geophysical research : Solid Earth > vol 126 n° 9 (September 2021) . - n° e2021JB022370 Titre : Influence of aperiodic non-tidal atmospheric and oceanic loading deformations on the stochastic properties of global GNSS vertical land motion time series Type de document : Article/Communication Auteurs : Kevin Gobron, Auteur ; Paul Rebischung , Auteur ; Michel Van Camp, Auteur ; Alain Demoulin, Auteur ; Olivier de Viron, Auteur Année de publication : 2021 Projets : 3-projet - voir note / Article en page(s) : n° e2021JB022370 Note générale : bibliographie This study has been financially supported by the Direction Générale de l’Armement (DGA), the Nouvelle-Aquitaine region, and the Centre National des Etudes Spatiales (CNES) as an application of the geodesy missions. This research was also supported by the Brain LASUGEO project entitled ”monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements” funded by the Belgian Sciences Policy. This is IPGP contribution number 4214. Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] coordonnées GNSS [Termes IGN] déformation verticale de la croute terrestre [Termes IGN] erreur systématique [Termes IGN] résidu [Termes IGN] série temporelle [Termes IGN] station permanente [Termes IGN] surcharge atmosphérique [Termes IGN] surcharge océanique Résumé : (auteur) Monitoring vertical land motions (VLMs) at the level of 0.1 mm/yr remains one of the most challenging scientific applications of global navigation satellite systems (GNSS). Such small rates of change can result from climatic and tectonic phenomena, and their detection is important to many solid Earth-related studies, including the prediction of coastal sea-level change and the understanding of intraplate deformation. Reaching a level of precision allowing to detect such small signals requires a thorough understanding of the stochastic variability in GNSS VLM time series. This paper investigates how the aperiodic part of non-tidal atmospheric and oceanic loading (NTAOL) deformations influences the stochastic properties of VLM time series. Using the time series of over 10,000 stations, we describe the impact of correcting for NTAOL deformation on 5 complementary metrics, namely: the repeatability of position residuals, the power-spectrum of position residuals, the estimated time-correlation properties, the corresponding velocity uncertainties, and the spatial correlation of the residuals. We show that NTAOL deformations cause a latitude-dependent bias in white noise plus power-law model parameter estimates. This bias is significantly mitigated when correcting for NTAOL deformation, which reduces velocity uncertainties at high latitudes by 70%. Therefore, removing NTAOL deformation before the statistical analysis of VLM time series might help to detect subtle VLM signals in these areas. Our spatial correlation analysis also reveals a seasonality in the spatial correlation of the residuals, which is reduced after removing NTAOL deformation, confirming that NTAOL is a clear source of common-mode errors in GNSS VLM time series. Numéro de notice : A2021-783 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Autre URL associée : vers HAL Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2021JB022370 Date de publication en ligne : 01/09/2021 En ligne : https://doi.org/10.1029/2021JB022370 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=98954 [article]

Statistical analysis of vertical land motions and sea level measurements at the coast / Kevin Gobron (2021)  

Public Titre : Statistical analysis of vertical land motions and sea level measurements at the coast Titre original : Analyse statistique des mesures des mouvement verticaux du sol et du niveau de la mer à la côte Type de document : Thèse/HDR Auteurs : Kevin Gobron, Auteur ; Olivier de Viron, Directeur de thèse ; Michel Van Camp, Directeur de thèse Editeur : La Rochelle : Université de La Rochelle Année de publication : 2021 Autre Editeur : Liège [Belgique] : Université de Liège (siège) Importance : 212 p. Format : 21 x 30 cm Note générale : bibliographie Thèse en co-tutelle présentée pour obtenir le grade de Docteur de La Rochelle Université et et de Docteur en Sciences de Liège Université, Discipline : Terre solide et enveloppes superficielles Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] aménagement du littoral [Termes IGN] amplitude [Termes IGN] bruit blanc [Termes IGN] déformation verticale de la croute terrestre [Termes IGN] données marégraphiques [Termes IGN] méthode du maximum de vraisemblance (estimation) [Termes IGN] modèle stochastique [Termes IGN] montée du niveau de la mer [Termes IGN] positionnement par GNSS [Termes IGN] série temporelle [Termes IGN] surcharge océanique Index. décimale : THESE Thèses et HDR Résumé : (auteur) Assurer la stabilité à long-terme des mesures du niveau de la mer à la côte est un enjeu essentiel à une gestion durable des territoires littoraux. Pour ce faire, les scientifiques reposent essentiellement sur deux techniques de mesure complémentaires : la marégraphie, qui permet de mesurer l’évolution du niveau de la mer par rapport à la côte, et la géodésie spatiale, qui permet de mesurer les mouvements verticaux de la côte elle-même, par rapport au centre de la terre. Ces techniques sont complémentaires car la correction des mouvements verticaux estimés par géodésie permet d’obtenir des mesures géocentriques du niveau de la mer à la cote, et donc de mieux comprendre l’origine des changements du niveau de la mer. Afin d’estimer et améliorer la stabilité et la qualité de ces deux sources d’informations, cette thèse propose des développements méthodologiques dédiés à l’estimation de la précision de chaque type d’observation, et en étudie les sources d’erreurs potentielles. Note de contenu : 1- Introduction 2- Estimation of deterministic parameters from observations 3- Estimation of stochastic parameters from observations 4- Elements of geodetic time series analysis 5- Event detection using hypothesis testing in linear models 6- Assessment of tide gauge sensor offsets in the presence of scale errors 7- Assessment of tide gauges biases and precisions by the combination of multiple co-located time series 8- Investigating the potential of the nonlinear LS-VCE method for the stochastic modelling of GNSS position time series 9- Impact of offsets on the stochastic modelling of GNSS position time series 10- Spatial and temporal properties of the stochastic variability in the position time series of over 10,000 stations 11- Influence of non-tidal atmospheric and oceanic loading on the stochastic properties of vertical land motion time series 12- Conclusions & perspectives Numéro de notice : 28669 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse française Note de thèse : Thèse de Doctorat : Terre solide et enveloppes superficielles : La Rochelle : 2021 Organisme de stage : Laboratoire Littoral, Environnement et Sociétés LIENs DOI : sans En ligne : https://tel.archives-ouvertes.fr/tel-03566564 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=99881

Vertical land motion in the Southwest and Central Pacific from available GNSS solutions and implications for relative sea levels / Valérie Ballu in Geophysical journal international, vol 218 n° 3 (September 2019)  

Public [article]  inGeophysical journal international > vol 218 n° 3 (September 2019) . - pp 1537 - 1551 Titre : Vertical land motion in the Southwest and Central Pacific from available GNSS solutions and implications for relative sea levels Type de document : Article/Communication Auteurs : Valérie Ballu, Auteur ; Médéric Gravelle, Auteur ; Guy Wöppelmann , Auteur ; Olivier de Viron, Auteur ; Paul Rebischung , Auteur ; Mélanie Becker, Auteur ; Pierre Sakic-Kieffer, Auteur Année de publication : 2019 Projets : STORISK / Duvat, Virginie, TOSCA / Duvat, Virginie Article en page(s) : pp 1537 - 1551 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] déformation verticale de la croute terrestre [Termes IGN] données GNSS [Termes IGN] incertitude géométrique [Termes IGN] montée du niveau de la mer [Termes IGN] Pacifique ouest [Termes IGN] Pacifique Sud [Termes IGN] série temporelle Résumé : (auteur) Coastal populations are impacted by relative sea level variations, which consist both of absolute sea level variations and of vertical land motions. This paper focuses on the Southwest and Central Pacific region, a recognized vulnerable region to sea level rise and where a large range of vertical land motion dynamics is observed. We analyse vertical displacement rates obtained from Global Navigation Satellite Systems (GNSS) by different analysis centres. We study the role played by modelled parameters, such as step discontinuities (due to equipment changes, earthquakes, etc.), in the position time-series analysis. We propose a new modelling approach based on a joint inversion of GNSS position time-series from different analysis centres. The final uncertainty on the vertical land motion rates is estimated as a combination of the uncertainty due to the GNSS data processing itself and the uncertainty due to the stability of the reference frame in which the GNSS data are expressed. We find that the dominant trend in the Southwest and Central Pacific is a moderate subsidence, with an average rate of −1.1 mm yr–1, but significant variations are observed, with displacement rates varying from an uplift of 1.6 ± 0.3 mm yr–1 to a subsidence of −5.4 ± 0.3 mm yr–1. Taking into account the geodynamic context, we assess, for each station, the relevance of current estimates of linear vertical displacement rate and uncertainty for forecasting future coastal sea levels. Numéro de notice : A2019-634 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1093/gji/ggz247 Date de publication en ligne : 27/05/2019 En ligne : https://doi.org/10.1093/gji/ggz247 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95452 [article]

Construction of bulk temperature/salinity from surface temperature and atlas profiles for monitoring water volume variations in the Caspian Sea / Ayoub Moradi (2019)  

Public Titre : Construction of bulk temperature/salinity from surface temperature and atlas profiles for monitoring water volume variations in the Caspian Sea Type de document : Article/Communication Auteurs : Ayoub Moradi, Auteur ; Olivier de Viron, Auteur ; Laurent Métivier , Auteur ; Saeid Homayouni, Auteur Editeur : Téhéran : Kharazmi University Année de publication : 2019 Conférence : CICIS 2019, 4th Conference on Contemporary Issues in Computer Information and Sciences 23/01/2019 25/01/2019 Teheran Iran Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] analyse de sensibilité [Termes IGN] Caspienne, mer [Termes IGN] image NOAA [Termes IGN] montée du niveau de la mer [Termes IGN] salinité [Termes IGN] température de surface de la mer Résumé : (auteur) Unlike the other lakes, the Caspian Sea has regular water level fluctuations caused by variation in temperature and salinity, which is known as thermohaline fluctuations. Vertically variable temperature and salinity data are needed in order to monitor thermohaline fluctuations. These data are regularly recorded for the open seas by remote sensing and in-situ approaches. However, there is no such information for inland water bodies, such as the Caspian Sea. In this research, daily Sea Surface Temperature (SST) from the NOAA satellite, plus long-term mean temperature, and salinity datasets from Atlas 2009 were utilized to construct bulk temperature and salinity in the Caspian Sea. The Atlas vertical profiles are not deep enough in the Caspian Sea; we expanded these data down to a thermocline depth, using a linear fitting. Constructed bulk temperature and salinity data utilized in water density calculations. The results show that thermohaline level fluctuation estimated by constructed bulk data is consisted of what a combination of altimetry and gravimetry system observed in the Caspian Sea. In the absence of necessary data, this method is helpful for bulk temperature and salinity estimations in the Caspian Sea with a satisfactory level of accuracy. The estimated thermohaline has an accuracy of about 93%, under the situation that there was 15% error in the estimation of both bulk temperature and salinity. Numéro de notice : C2019-080 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Thématique : IMAGERIE Nature : Communication DOI : sans En ligne : https://www.researchgate.net/publication/368243402_Construction_of_Bulk_Temperat [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102859

Direct measurement of evapotranspiration from a forest using a superconducting gravimeter / Michel Van Camp in Geophysical research letters, vol 43 n° 19 (15 October 2016)    

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Optimized strategy for the calibration of superconducting gravimeters at the one per mille level / Michel Van Camp in Journal of geodesy, vol 90 n° 1 (January 2016)  

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Impact of the North Atlantic oscillation on Southern Europe water distribution: insights from geodetic data / Pierre Valty in Earth Interactions, vol 19 n° 10 (September 2015)    

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Les effets de l'oscillation Nord-Atlantique sur les transferts de masse, vus par géodésie / Pierre Valty in XYZ, n° 139 (juin - août 2014) 

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The quest for a consistent signal in ground and GRACE gravity time-series / Michel Van Camp in Geophysical journal international, vol 197 n° 1 (April 2014)  

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Comparative study of temporal variations in the earth’s gravity field using GRACE gravity models in the regions of three recent giant earthquakes / Valentin O. Mikhailov in Izvestiya, Physics of the Solid Earth, vol 50 n° 2 (March 2014)  

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Evaluation of MODIS data for improved monitoring of the Caspian Sea / Ayoub Moradi in International Journal of Remote Sensing IJRS, vol 35 n° 16 (January 2014)  

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Multi sensor study of hydrological changes in Caspian Sea / Ayoub Moradi (sept 2014)

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Assessing the precision in loading estimates by geodetic techniques in Southern Europe / Pierre Valty in Geophysical journal international, vol 194 n° 3 (September 2013)    

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Numerical modelling of post-seismic rupture propagation after the Sumatra 26.12.2004 earthquake constrained by GRACE gravity data / Valentin O. Mikhailov in Geophysical journal international, vol 194 n° 2 (August 2013)  

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