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Improving the modeling of the atmospheric delay in the data analysis of the Intensive VLBI sessions and the impact on the UT1 estimates / Tobias Nilsson in Journal of geodesy, vol 91 n° 7 (July 2017)  

Public [article]  inJournal of geodesy > vol 91 n° 7 (July 2017) . - pp 857 - 866 Titre : Improving the modeling of the atmospheric delay in the data analysis of the Intensive VLBI sessions and the impact on the UT1 estimates Type de document : Article/Communication Auteurs : Tobias Nilsson, Auteur ; Benedikt Soja, Auteur ; Kyriakos Balidakis, Auteur ; Maria Karbon, Auteur ; Robert Heinkelmann, Auteur ; Zhiguo Deng, Auteur ; Harald Schuh, Auteur Année de publication : 2017 Article en page(s) : pp 857 - 866 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse de données [Termes IGN] filtre de Kalman [Termes IGN] gradient de troposphère [Termes IGN] interférométrie à très grande base [Termes IGN] longueur du jour [Termes IGN] modèle atmosphérique [Termes IGN] retard troposphérique zénithal [Termes IGN] temps universel Résumé : (Auteur) The very long baseline interferometry (VLBI) Intensive sessions are typically 1-h and single-baseline VLBI sessions, specifically designed to yield low-latency estimates of UT1-UTC. In this work, we investigate what accuracy is obtained from these sessions and how it can be improved. In particular, we study the modeling of the troposphere in the data analysis. The impact of including external information on the zenith wet delays (ZWD) and tropospheric gradients from GPS or numerical weather prediction models is studied. Additionally, we test estimating tropospheric gradients in the data analysis, which is normally not done. To evaluate the results, we compared the UT1-UTC values from the Intensives to those from simultaneous 24-h VLBI session. Furthermore, we calculated length of day (LOD) estimates using the UT1-UTC values from consecutive Intensives and compared these to the LOD estimated by GPS. We find that there is not much benefit in using external ZWD; however, including external information on the gradients improves the agreement with the reference data. If gradients are estimated in the data analysis, and appropriate constraints are applied, the WRMS difference w.r.t. UT1-UTC from 24-h sessions is reduced by 5% and the WRMS difference w.r.t. the LOD from GPS by up to 12%. The best agreement between Intensives and the reference time series is obtained when using both external gradients from GPS and additionally estimating gradients in the data analysis. Numéro de notice : A2017-298 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-016-0985-7 En ligne : http://doi.org/10.1007/s00190-016-0985-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85333 [article]

The extension of the parametrization of the radio source coordinates in geodetic VLBI and its impact on the time series analysis / Maria Karbon in Journal of geodesy, vol 91 n° 7 (July 2017)  

Public [article]  inJournal of geodesy > vol 91 n° 7 (July 2017) . - pp 755 - 765 Titre : The extension of the parametrization of the radio source coordinates in geodetic VLBI and its impact on the time series analysis Type de document : Article/Communication Auteurs : Maria Karbon, Auteur ; Robert Heinkelmann, Auteur ; Julian Mora-Diaz, Auteur ; Minghui Xu, Auteur ; Tobias Nilsson, Auteur ; Harald Schuh, Auteur Année de publication : 2017 Article en page(s) : pp 755 - 765 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] données ITGB [Termes IGN] fonction spline [Termes IGN] interférométrie à très grande base [Termes IGN] paramètres d'orientation de la Terre [Termes IGN] régression multivariée par spline adaptative [Termes IGN] repère de référence céleste [Termes IGN] série temporelle Résumé : (Auteur) The radio sources within the most recent celestial reference frame (CRF) catalog ICRF2 are represented by a single, time-invariant coordinate pair. The datum sources were chosen mainly according to certain statistical properties of their position time series. Yet, such statistics are not applicable unconditionally, and also ambiguous. However, ignoring systematics in the source positions of the datum sources inevitably leads to a degradation of the quality of the frame and, therefore, also of the derived quantities such as the Earth orientation parameters. One possible approach to overcome these deficiencies is to extend the parametrization of the source positions, similarly to what is done for the station positions. We decided to use the multivariate adaptive regression splines algorithm to parametrize the source coordinates. It allows a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. The algorithm finds the ideal knot positions for the splines and, thus, the best number of polynomial pieces to fit the data autonomously. With that we can correct the ICRF2 a priori coordinates for our analysis and eliminate the systematics in the position estimates. This allows us to introduce also special handling sources into the datum definition, leading to on average 30 % more sources in the datum. We find that not only the CPO can be improved by more than 10 % due to the improved geometry, but also the station positions, especially in the early years of VLBI, can benefit greatly. Numéro de notice : A2017-296 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-016-0954-1 En ligne : http://doi.org/10.1007/s00190-016-0954-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85331 [article]

Earth orientation parameters estimated from VLBI during the CONT11 campaign / Tobias Nilsson in Journal of geodesy, vol 88 n° 5 (May 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 5 (May 2014) . - pp 491 - 491 Titre : Earth orientation parameters estimated from VLBI during the CONT11 campaign Type de document : Article/Communication Auteurs : Tobias Nilsson, Auteur ; Robert Heinkelmann, Auteur ; Maria Karbon, Auteur ; Virginia Raposo-Pulibo, Auteur ; Harald Schuh, Auteur Année de publication : 2014 Article en page(s) : pp 491 - 491 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] données ITGB [Termes IGN] méthode de Monte-Carlo [Termes IGN] orientation de la Terre [Termes IGN] positionnement par ITGB [Termes IGN] série temporelle Résumé : (Auteur) In this paper, we investigate the accuracy of the earth orientation parameters (EOP) estimated from the continuous VLBI campaign CONT11. We first estimated EOP with daily resolution and compared these to EOP estimated from GNSS data. We find that the WRMS differences are about 31 u as for polar motion and 7 u s for length of day. This is about the precision we could expect, based on Monte Carlo simulations and the results of the previous CONT campaigns. We also estimated EOP with hourly resolution to study the sub-diurnal variations. The results confirm the results of previous studies, showing that the current IERS model for high-frequency EOP variations does not explain all the sub-diurnal variations seen in the estimated time series. We then compared our results to various empirical high-frequency EOP models. However, we did not find that any of these gave any unambiguous improvement. Several simulations testing the impact of various aspects of, e.g. the observing network were also made. For example, we made simulations assuming that all CONT11 stations were equipped with fast VLBI2010 antennas. We found that the WRMS error decreased by about a factor five compared to the current VLBI system. Furthermore, the simulations showed that it is very important to have a homogenous global distribution of the stations for achieving the highest precision for the EOP. Numéro de notice : A2014-257 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0700-5 Date de publication en ligne : 21/02/2014 En ligne : https://doi.org/10.1007/s00190-014-0700-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33160 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2014051	SL	Revue	Centre de documentation	Revues en salle	Disponible

Atmospheric effects on measurements of the Earth gravity field / Maria Karbon (2013)  

Public Titre : Atmospheric effects on measurements of the Earth gravity field Type de document : Thèse/HDR Auteurs : Maria Karbon, Auteur Editeur : Vienne [Autriche] : Technische Universität Wien Année de publication : 2013 Collection : Geowissenschaftliche Mitteilungen, ISSN 1811-8380 num. 94 Importance : 150 p. Format : 21 x 30 cm Note générale : bibliographie Diese Arbeit wurde an der Fakultät für Mathematik und Geoinformation der Technischen Universität Wien zur Erlangung des akademischen Grades einer Doktorin der technischen Wissenschaften eingereicht Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] correction atmosphérique [Termes IGN] données GRACE [Termes IGN] effet atmosphérique [Termes IGN] gravimètre supraconducteur [Termes IGN] marée terrestre [Termes IGN] modèle mathématique [Termes IGN] rotation de la Terre [Termes IGN] surcharge atmosphérique [Termes IGN] surcharge océanique Index. décimale : 30.40 Géodésie physique Résumé : (auteur) Atmospheric pressure variations are one of the major sources of surface gravity perturbations. The varying atmosphere introduces two disturbing forces in the gravity signal, the so called direct effect or Newtonian attraction, where the measuring object is attracted by the atmospheric mass itself, and secondly the indirect effect or atmospheric loading, where the masses deform the Earth’s surface, what again influences the measured gravity signal due to the slightly changes gravity field. In satellite gravity missions such signals are referred to as aliasing. To eliminate them, the de- termination of accurate atmospheric gravity field coefficients (AGC) is indispensable. For the determination of AGC it is state of the art to use high resolution numerical weather models which take into account the time-variable three-dimensional distribution of the atmospheric mass. By subtracting the gravity spherical harmonics of the instantaneous atmosphere from the ones of a long term mean field, the residual gravity spherical harmonic series is obtained. It describes the deviation of the actual gravity field from the mean gravity field due to atmospheric mass variations. Ground based gravimetric measurements encounter the same difficulty of eliminating the disturbing signal introduced by the atmosphere. Superconducting gravimeters are usually corrected using the local air pressure, which reduces up to 90-95 % of the atmospheric signal. However, modern superconducting gravimeters require an even better atmospheric correction if small signals are to be identified. For this task the use of three-dimensional modeling of atmospheric mass attraction based on operational numerical weather models has shown promising results. Note de contenu : 1. Introduction 2. The gravity field of the Earth 3. Atmospheric effects on the gravity field of the Earth 4. Mathematical description of the de-aliasing model for GRACE and its validation 5. Atmospheric corrections for superconducting gravimeters 6. Conclusion and outlook Numéro de notice : 14939 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : PhD : Mathematik und Geoinformation : Wien : 2013 En ligne : http://www.ub.tuwien.ac.at/diss/AC07815618.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=77497