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Assessment of the accuracy of global geodetic satellite laser ranging observations and estimated impact on ITRF scale: estimation of systematic errors in LAGEOS observations 1993–2014 / Graham Appleby in Journal of geodesy, vol 90 n° 12 (December 2016)  

Public [article]  inJournal of geodesy > vol 90 n° 12 (December 2016) . - pp 1371 - 1388 Titre : Assessment of the accuracy of global geodetic satellite laser ranging observations and estimated impact on ITRF scale: estimation of systematic errors in LAGEOS observations 1993–2014 Type de document : Article/Communication Auteurs : Graham Appleby, Auteur ; José Rodríguez, Auteur ; Zuheir Altamimi , Auteur Année de publication : 2016 Article en page(s) : pp 1371 - 1388 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] analyse diachronique [Termes descripteurs IGN] champ de gravitation [Termes descripteurs IGN] constante [Termes descripteurs IGN] données Lageos [Termes descripteurs IGN] données TLS (télémétrie) [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] géocentre [Termes descripteurs IGN] système de référence géodésique Résumé : (Auteur) Satellite laser ranging (SLR) to the geodetic satellites LAGEOS and LAGEOS-2 uniquely determines the origin of the terrestrial reference frame and, jointly with very long baseline interferometry, its scale. Given such a fundamental role in satellite geodesy, it is crucial that any systematic errors in either technique are at an absolute minimum as efforts continue to realise the reference frame at millimetre levels of accuracy to meet the present and future science requirements. Here, we examine the intrinsic accuracy of SLR measurements made by tracking stations of the International Laser Ranging Service using normal point observations of the two LAGEOS satellites in the period 1993 to 2014. The approach we investigate in this paper is to compute weekly reference frame solutions solving for satellite initial state vectors, station coordinates and daily Earth orientation parameters, estimating along with these weekly average range errors for each and every one of the observing stations. Potential issues in any of the large number of SLR stations assumed to have been free of error in previous realisations of the ITRF may have been absorbed in the reference frame, primarily in station height. Likewise, systematic range errors estimated against a fixed frame that may itself suffer from accuracy issues will absorb network-wide problems into station-specific results. Our results suggest that in the past two decades, the scale of the ITRF derived from the SLR technique has been close to 0.7 ppb too small, due to systematic errors either or both in the range measurements and their treatment. We discuss these results in the context of preparations for ITRF2014 and additionally consider the impact of this work on the currently adopted value of the geocentric gravitational constant, GM. Numéro de notice : A2016-808 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-016-0929-2 date de publication en ligne : 29/06/2016 En ligne : http://dx.doi.org/10.1007/s00190-016-0929-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=82596 [article]

Comparison of Satellite-Only Gravity Field Models Constructed with All and Parts of the GOCE Gravity Gradient Dataset / Sean L. Bruinsma in Marine geodesy, vol 39 n° 3-4 (March - June 2016)  

Public [article]  inMarine geodesy > vol 39 n° 3-4 (March - June 2016) . - pp 238 - 255 Titre : Comparison of Satellite-Only Gravity Field Models Constructed with All and Parts of the GOCE Gravity Gradient Dataset Type de document : Article/Communication Auteurs : Sean L. Bruinsma, Auteur ; Christoph Förste, Auteur ; Sandrine Mulet, Auteur ; Marie-Hélène Rio, Auteur ; et al., Auteur Année de publication : 2016 Article en page(s) : pp 238 - 255 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] circulation géostrophique [Termes descripteurs IGN] données GOCE [Termes descripteurs IGN] données Lageos [Termes descripteurs IGN] gradient de gravitation [Termes descripteurs IGN] modèle de géopotentiel Résumé : (auteur) The impact of GOCE Satellite Gravity Gradiometer data on gravity field models was tested. All models were constructed with the same Laser Geodynamics Satellite (LAGEOS) and Gravity Recovery and Climate Experiment (GRACE) data, which were combined with one or two of the diagonal gravity gradient components for the entire GOCE mission (November 2009 to October 2013). The Stokes coefficients were estimated by solving large normal equation (NE) systems (i.e., the direct numerical approach). The models were evaluated through comparisons with the European Space Agency's (ESA) gravity field model DIR-R5, by GPS/Leveling, GOCE orbit determination, and geostrophic current evaluations. Among the single gradient models, only the model constructed with the vertical ZZ gradients gave good results that were in agreement with the formal errors. The model based only on XX gradients is the least accurate. The orbit results for all models are very close and confirm this finding. All models constructed with two diagonal gradient components are more accurate than the ZZ-only model due to doubling the amount of data and having two complementary observation directions. This translates also to a slower increase of model errors with spatial resolution. The different evaluation methods cannot unambiguously identify the most accurate two-component model. They do not always agree, emphasizing the importance of evaluating models using many different methods. The XZ gravity gradient gives a small positive contribution to model accuracy. Numéro de notice : A2016-965 Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1080/01490419.2016.1182090 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83616 [article]

Determination of precise satellite orbits and geodetic parameters using satellite laser ranging / Krzysztof Sosnica (2015)  

Public Titre : Determination of precise satellite orbits and geodetic parameters using satellite laser ranging Type de document : Rapport Auteurs : Krzysztof Sosnica, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2015 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 93 Importance : 257 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-38-3 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] Bernese [Termes descripteurs IGN] données Ajisai [Termes descripteurs IGN] données Lageos [Termes descripteurs IGN] données Starlette [Termes descripteurs IGN] données Stella [Termes descripteurs IGN] géocentre [Termes descripteurs IGN] Global Geodetic Observing System [Termes descripteurs IGN] orbite basse [Termes descripteurs IGN] perturbation orbitale [Termes descripteurs IGN] repère de référence [Termes descripteurs IGN] rotation de la Terre [Termes descripteurs IGN] satellite de télémétrie [Termes descripteurs IGN] télémétrie laser sur satellite Index. décimale : 30.63 Télémétrie laser sur satellite, Télémétrie laser sur lune, VLBI Résumé : (auteur) The contribution of the SLR to the definition of the origin of reference frame (geocenter coordinates), the global scale (in both the geometric and dynamic sense), and low degree coefficients of the Earth's gravity field (especially the oblateness term) is essential, due to the high stability of satellite orbits and the exceptional precision of SLR observations, which are affected only by few error sources. Moreover, the SLR technique has a great contribution to a definition of the global terrestrial reference frame, estimation of the Earth rotation parameters and the time variable Earth's gravity field. The long time series of precise SLR observations allow validating many models, e.g., ocean tide models, Earth gravity field models, atmospheric pressure loading models, atmosphere and ocean induced time variable gravity field models, etc. We have shown that appropriate modeling of gravitational and non-gravitational forces is essential for orbit determination of geodetic satellites. Concerning the gravitational forces, the coefficient C20 couses the largest perturbations on LAGEOS satellites. The sensitivity of LAGEOS orbits dramatically decreases for higher degree geopotential coefficients, whereas low orbiting geodetic satellites are very sensitive to both, low- and medium-degree coefficients of the Earth's gravity field. The differences between the current ocean tide models have bigger impact on LAGEOS orbits than the differences between the current Earth gravity field models. The mean differences between solutions using various ocean tide models (max. 1.32 mm of RMS) are larger than the mean differences between orbit solutions using various Earth gravity field models (max. 1.16 mm of RMS). Insufficient quality of the S2 tide constituent causes large variations of the empirical orbit parameters of SLR geodetic satellites, as well as variations for different type satellites, e.g., GRACE. The atmospheric drag causes a secular decay of semi-major axes of low orbiting geodetic satellites, i.e., Starlette, Stella, and AJISAI, whereas the Yarkovsky and the Yarkovsky- Schach effects cause a secular decay of LAGEOS-1 and LAGEOS-2. The decay of the semi-major axis of LAGEOS-1 is smaller than the decay reported in many earlier papers due to the satellite's de-spinning effect. The decay is fiaL1 = Note de contenu : 1 Introduction 1.1 Role of Satellite Laser Ranging in Science 1.2 Objectives and Methods 1.3 Structure 2 Satellite Geodesy 2.1 Reference Systems and Frames 2.2 Satellite Orbit Modeling 2.3 Parameter Estimation Using the Least-Squares Method 2.4 Global Navigation Satellite Systems (GNSS) 2.5 Satellite Laser Ranging 3 Gravitational Forces Acting on Geodetic Satellites 3.1 Solution Description 3.2 LAGEOS Sensitivity to Earth Gravity Field Models 3.3 LAGEOS Sensitivity to Ocean Tide Models 3.4 Discussion and Conclusions 4 Non-gravitational Forces Acting on Geodetic Satellites 4.1 Thermal effects 4.2 Earth Radiation Pressure 4.3 Atmospheric Drag 4.4 Discussion and Conclusions 5 Improving SLR Solutions 5.1 Impact of Loading Corrections on SLR Solutions 5.2 The Blue-Sky effect 5.3 Orbit Modeling of Low Orbiting Geodetic Satellites 5.4 Combined LAGEOS-LEO Solutions 5.5 Simultaneous Estimation of Gravity Field along with other Parameters 5.6 Time Variable Earth's Gravity Field From SLR 5.7 Discussion and Conclusions Numéro de notice : 14914 Thématique : POSITIONNEMENT Nature : Rapport de recherche En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-93.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76821

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Laser ranging data analysis for a colocation campaign of French Transportable Laser Ranging System (FTLRS) in Tahiti / Xiaoni Wang in Journal of geodesy, vol 89 n° 1 (January 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 1 (January 2015) . - pp 1 - 11 Titre : Laser ranging data analysis for a colocation campaign of French Transportable Laser Ranging System (FTLRS) in Tahiti Type de document : Article/Communication Auteurs : Xiaoni Wang, Auteur ; Pascal Bonnefond, Auteur ; Pierre Exertier, Auteur ; David Coulot , Auteur ; Richard Biancale, Auteur ; Jean-Michel Lemoine, Auteur ; Jean-Claude Poyard, Auteur ; C. Courde, Auteur ; Jean-Pierre Barriot, Auteur ; François Barlier, Auteur Année de publication : 2015 Article en page(s) : pp 1 - 11 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] analyse comparative [Termes descripteurs IGN] co-positionnement [Termes descripteurs IGN] données DORIS [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] données Lageos [Termes descripteurs IGN] données Starlette [Termes descripteurs IGN] données TLS (télémétrie) [Termes descripteurs IGN] International Terrestrial Reference Frame [Termes descripteurs IGN] point de liaison (géodésie) [Termes descripteurs IGN] Tahiti [Termes descripteurs IGN] télémétrie laser transportable Résumé : (auteur) Tahiti is a unique geodetic site located in the south Pacific Ocean where few observatories exist nearby. The American mobile station MOBLAS-8 was installed in Tahiti in 1998, and GPS and DORIS systems were also deployed in its vicinity in order to develop this site into one of the fundamental colocated sites of the International Terrestrial Reference Frame. In order to make a new estimate of the colocation differences between the different techniques, a campaign of the French Transportable Laser Ranging System (FTLRS) was conducted in Tahiti between April and October 2011. The FTLRS was deployed close to the existing equipment. Observations for LAGEOS 1, LAGEOS 2 and Starlette were studied, and the solutions to the local ties between FTLRS, MOBLAS-8, DORIS and GPS were evaluated. Our results of the geodetic local-ties between laser stations and GPS agree well with the measurements made by the Institut National de l’Information Géographique et Forestière (IGN) during the campaign, with differences less than 2 mm in the vertical direction. The laser station range biases as a function of satellites are also presented, −3 (±2) mm for MOBLAS-8 and 3 (±3) mm for FTLRS, respectively. In addition, we investigated the role of time bias (ranging from a few hundreds of nanoseconds to one microsecond) given by the Time Transfer by Laser Link experiment, which shows a limited impact on the present SLR analysis. We also compared the coordinates of the three available techniques at Tahiti, i.e., laser, GPS and DORIS. We found the accuracy of laser solutions still needs to be improved, so that the SLR at Tahiti could contribute more effectively to the tracking of satellites and thus to the international reference frame. This study is useful in evaluating the SLR and other space techniques in order to prepare the deployment of new equipment in Tahiti in the near future. Numéro de notice : A2015-230 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0755-3 En ligne : https://doi.org/10.1007/s00190-014-0755-3 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76064 [article]

Estimated SLR station position and network frame sensitivity to time-varying gravity / Nikita P. Zelensky in Journal of geodesy, vol 88 n° 6 (June 2014)  

Public [article]  inJournal of geodesy > vol 88 n° 6 (June 2014) . - pp 517 - 537 Titre : Estimated SLR station position and network frame sensitivity to time-varying gravity Type de document : Article/Communication Auteurs : Nikita P. Zelensky, Auteur ; Franck G. Lemoine, Auteur ; Douglas S. Chinn, Auteur ; Stravos Melachroinos, Auteur ; et al., Auteur Année de publication : 2014 Article en page(s) : pp 517 - 537 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géographie physique [Termes descripteurs IGN] données Lageos [Termes descripteurs IGN] gravité normale [Termes descripteurs IGN] orbitographie [Termes descripteurs IGN] paramètre de temps [Termes descripteurs IGN] station TLS (télémétrie) Résumé : (Auteur) This paper evaluates the sensitivity of ITRF2008-based satellite laser ranging (SLR) station positions estimated weekly using LAGEOS-1/2 data from 1993 to 2012 to non-tidal time-varying gravity (TVG). Two primary methods for modeling TVG from degree-2 are employed. The operational approach applies an annual GRACE-derived field, and IERS recommended linear rates for five coefficients. The experimental approach uses low-order/degree 44 coefficients estimated weekly from SLR and DORIS processing of up to 11 satellites (tvg4x4). This study shows that the LAGEOS-1/2 orbits and the weekly station solutions are sensitive to more detailed modeling of TVG than prescribed in the current IERS standards. Over 1993–2012 tvg4x4 improves SLR residuals by 18 % and shows 10 % RMS improvement in station stability. Tests suggest that the improved stability of the tvg4x4 POD solution frame may help clarify geophysical signals present in the estimated station position time series. The signals include linear and seasonal station motion, and motion of the TRF origin, particularly in Z. The effect on both POD and the station solutions becomes increasingly evident starting in 2006. Over 2008–2012, the tvg4x4 series improves SLR residuals by 29 %. Use of the GRGS RL02 5050 series shows similar improvement in POD. Using tvg4x4, secular changes in the TRF origin Z component double over the last decade and although not conclusive, it is consistent with increased geocenter rate expected due to continental ice melt. The test results indicate that accurate modeling of TVG is necessary for improvement of station position estimation using SLR data Numéro de notice : A2014-286 Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0701-4 date de publication en ligne : 06/03/2014 En ligne : https://doi.org/10.1007/s00190-014-0701-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33189 [article]

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Etude de l'impact d'un modèle de surcharges sur les résultats obtenus par télémétrie laser sur satellites / Goulven Tallec (2014) 

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Restitution d'orbites de débris spatiaux par algorithmes génétiques / Mohamed-Amjad Lasri (2014) 

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