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A hybrid approach for recovering high-resolution temporal gravity fields from satellite laser ranging / Anno Löcher in Journal of geodesy, vol 95 n° 1 (January 2021)  

Public [article]  inJournal of geodesy > vol 95 n° 1 (January 2021) . - n° 6 Titre : A hybrid approach for recovering high-resolution temporal gravity fields from satellite laser ranging Type de document : Article/Communication Auteurs : Anno Löcher, Auteur ; Jürgen Kusche, Auteur Année de publication : 2021 Article en page(s) : n° 6 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] changement temporel [Termes IGN] données GRACE [Termes IGN] données TLS (télémétrie) [Termes IGN] facteur d'échelle [Termes IGN] fonction orthogonale [Termes IGN] harmonique sphérique [Termes IGN] modélisation [Termes IGN] série temporelle Résumé : (auteur) A new approach to recover time-variable gravity fields from satellite laser ranging (SLR) is presented. It takes up the concept of lumped coefficients by representing the temporal changes of the Earth’s gravity field by spatial patterns via combinations of spherical harmonics. These patterns are derived from the GRACE mission by decomposing the series of monthly gravity field solutions into empirical orthogonal functions (EOFs). The basic idea of the approach is then to use the leading EOFs as base functions in the gravity field modelling and to adjust the respective scaling factors straightforward within the dynamic orbit computation; only for the lowest degrees, the spherical harmonic coefficients are estimated separately. As a result, the estimated gravity fields have formally the same spatial resolution as GRACE. It is shown that, within the GRACE time frame, both the secular and the seasonal signals in the GRACE time series are reproduced with high accuracy. In the period prior to GRACE, the SLR solutions are in good agreement with other techniques and models and confirm, for instance, that the Greenland ice sheet was stable until the late 1990s. Further validation is done with the first monthly fields from GRACE Follow-On, showing a similar agreement as with GRACE itself. Significant differences to the reference data only emerge occasionally when zooming into smaller river basins with strong interannual mass variations. In such cases, the approach reaches its limits which are set by the low spectral sensitivity of the SLR satellites and the strong constraints exerted by the EOFs. The benefit achieved by the enhanced spatial resolution has to be seen, therefore, primarily in the proper capturing of the mass signal in medium or large areas rather than in the opportunity to focus on isolated spatial details. Numéro de notice : A2021-026 Affiliation des auteurs : non IGN Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01460-x Date de publication en ligne : 23/12/2020 En ligne : https://doi.org/10.1007/s00190-020-01460-x Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96710 [article]

Introducing a vertical land motion model for improving estimates of sea level rates derived from tide gauge records affected by earthquakes / Anna Klos in GPS solutions, vol 23 n° 4 (October 2019)  

Public [article]  inGPS solutions > vol 23 n° 4 (October 2019) Titre : Introducing a vertical land motion model for improving estimates of sea level rates derived from tide gauge records affected by earthquakes Type de document : Article/Communication Auteurs : Anna Klos, Auteur ; Jürgen Kusche, Auteur ; L. Fenoglio-Marc, Auteur ; et al., Auteur Année de publication : 2019 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 marégraphiques [Termes IGN] marée océanique [Termes IGN] modèle de simulation [Termes IGN] montée du niveau de la mer [Termes IGN] niveau de la mer [Termes IGN] Pacifique (océan) [Termes IGN] positionnement par GPS [Termes IGN] séisme [Termes IGN] série temporelle Résumé : (Auteur) We reassess the absolute and relative sea level changes at 38 tide gauge stations in the earthquake-affected Western North Pacific for the 1993–2015 period, focusing on the vertical land motion (VLM) which is crucial for narrowing the gap between these estimates. In this area, simply discarding all earthquake-affected sites, one overestimates the average regional sea level rise by more than 0.5 mm/year. Disregarding VLM would lead to misestimating local sea level trends between 0.2 and 7.6 mm/year. If accounted for, but modeled as linear during the entire time span, VLM leads to regional absolute sea level rise errors of up to 0.4 mm/year. Therefore, we introduce a new methodology that better represents the Global Positioning System (GPS)-derived nonlinear VLM by accounting for co-seismic offsets, changes in the vertical velocities and post-seismic transient. Also, for the first time, a combination of white and power-law noises is added to this nonlinear model to derive proper uncertainties of VLM. We find a maximum difference of 15.3 mm/year between pre- and post-seismic vertical velocities. The GPS-sensed vertical co-seismic displacement approaches 36 mm. Assuming the changes in vertical velocities and displacement due to the tectonic movements is not accounted for, and then, estimating absolute sea level rise from tide gauges can result in an error of 10 mm/year. Introducing a new nonlinear VLM model improves absolute tide gauge sea level estimates by 20% on average. Finally, for the reconstructed Western North Pacific sea level, altimetry agrees best with tide gauge data corrected employing the new nonlinear VLM model. Numéro de notice : A2019-333 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-019-0896-1 Date de publication en ligne : 24/07/2019 En ligne : https://doi.org/10.1007/s10291-019-0896-1 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93422 [article]

A systematic impact assessment of GRACE error correlation on data assimilation in hydrological models / Maike Schumacher in Journal of geodesy, vol 90 n° 6 (June 2016)  

Public [article]  inJournal of geodesy > vol 90 n° 6 (June 2016) . - pp 537 – 559 Titre : A systematic impact assessment of GRACE error correlation on data assimilation in hydrological models Type de document : Article/Communication Auteurs : Maike Schumacher, Auteur ; Jürgen Kusche, Auteur ; Petra Döll, Auteur Année de publication : 2016 Article en page(s) : pp 537 – 559 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] bassin hydrographique [Termes IGN] corrélation [Termes IGN] données GRACE [Termes IGN] erreur [Termes IGN] filtre de Kalman [Termes IGN] gravimétrie [Termes IGN] Mississippi (fleuve) [Termes IGN] modèle hydrographique Résumé : (auteur) Recently, ensemble Kalman filters (EnKF) have found increasing application for merging hydrological models with total water storage anomaly (TWSA) fields from the Gravity Recovery And Climate Experiment (GRACE) satellite mission. Previous studies have disregarded the effect of spatially correlated errors of GRACE TWSA products in their investigations. Here, for the first time, we systematically assess the impact of the GRACE error correlation structure on EnKF data assimilation into a hydrological model, i.e. on estimated compartmental and total water storages and model parameter values. Our investigations include (1) assimilating gridded GRACE-derived TWSA into the WaterGAP Global Hydrology Model and, simultaneously, calibrating its parameters; (2) introducing GRACE observations on different spatial scales; (3) modelling observation errors as either spatially white or correlated in the assimilation procedure, and (4) replacing the standard EnKF algorithm by the square root analysis scheme or, alternatively, the singular evolutive interpolated Kalman filter. Results of a synthetic experiment designed for the Mississippi River Basin indicate that the hydrological parameters are sensitive to TWSA assimilation if spatial resolution of the observation data is sufficiently high. We find a significant influence of spatial error correlation on the adjusted water states and model parameters for all implemented filter variants, in particular for subbasins with a large discrepancy between observed and initially simulated TWSA and for north–south elongated sub-basins. Considering these correlated errors, however, does not generally improve results: while some metrics indicate that it is helpful to consider the full GRACE error covariance matrix, it appears to have an adverse effect on others. We conclude that considering the characteristics of GRACE error correlation is at least as important as the selection of the spatial discretisation of TWSA observations, while the choice of the filter method might rather be based on the computational simplicity and efficiency. Numéro de notice : A2016-422 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-016-0892-y Date de publication en ligne : 27/02/2016 En ligne : https://doi.org/10.1007/s00190-016-0892-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81314 [article]