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Combinatorial optimization applied to VLBI scheduling / A. Corbin in Journal of geodesy, vol 94 n°2 (February 2020)  

Public [article]  inJournal of geodesy > vol 94 n°2 (February 2020) Titre : Combinatorial optimization applied to VLBI scheduling Type de document : Article/Communication Auteurs : A. Corbin, Auteur ; B. Niedermann, Auteur ; Axel Nothnagel, Auteur ; et al., Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] analyse combinatoire (maths) [Termes descripteurs IGN] données VGOS [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] positionnement par ITGB [Termes descripteurs IGN] programmation linéaire [Termes descripteurs IGN] retard troposphérique zénithal [Termes descripteurs IGN] station VLBI [Termes descripteurs IGN] téléscope [Termes descripteurs IGN] temps universel coordonné Résumé : (auteur) Due to the advent of powerful solvers, today linear programming has seen many applications in production and routing. In this publication, we present mixed-integer linear programming as applied to scheduling geodetic very-long-baseline interferometry (VLBI) observations. The approach uses combinatorial optimization and formulates the scheduling task as a mixed-integer linear program. Within this new method, the schedule is considered as an entity containing all possible observations of an observing session at the same time, leading to a global optimum. In our example, the optimum is found by maximizing the sky coverage score. The sky coverage score is computed by a hierarchical partitioning of the local sky above each telescope into a number of cells. Each cell including at least one observation adds a certain gain to the score. The method is computationally expensive and this publication may be ahead of its time for large networks and large numbers of VLBI observations. However, considering that developments of solvers for combinatorial optimization are progressing rapidly and that computers increase in performance, the usefulness of this approach may come up again in some distant future. Nevertheless, readers may be prompted to look into these optimization methods already today seeing that they are available also in the geodetic literature. The validity of the concept and the applicability of the logic are demonstrated by evaluating test schedules for five 1-h, single-baseline Intensive VLBI sessions. Compared to schedules that were produced with the scheduling software sked, the number of observations per session is increased on average by three observations and the simulated precision of UT1-UTC is improved in four out of five cases (6 μs average improvement in quadrature). Moreover, a simplified and thus much faster version of the mixed-integer linear program has been developed for modern VLBI Global Observing System telescopes. Numéro de notice : A2020-153 Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01348-w date de publication en ligne : 29/01/2020 En ligne : https://doi.org/10.1007/s00190-020-01348-w Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94786 [article]

Systematic errors in SLR data and their impact on the ILRS products / Vincenza Luceri in Journal of geodesy, vol 93 n°11 (November 2019)  

Public [article]  inJournal of geodesy > vol 93 n°11 (November 2019) Titre : Systematic errors in SLR data and their impact on the ILRS products Type de document : Article/Communication Auteurs : Vincenza Luceri, Auteur ; M. Pirri, Auteur ; J. Rodriguez, Auteur ; et al., Auteur Année de publication : 2019 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] acquisition de données [Termes descripteurs IGN] contrôle qualité [Termes descripteurs IGN] données TLS (télémétrie) [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] International Terrestrial Reference Frame [Termes descripteurs IGN] qualité des données [Termes descripteurs IGN] rétroréflecteur [Termes descripteurs IGN] station TLS (télémétrie) [Termes descripteurs IGN] télémétrie laser sur satellite Résumé : (auteur) The satellite laser ranging (SLR) technique has the potential to make extremely precise measurements to retroreflector arrays on orbiting satellites, with normal point range precision at a level of 1 mm for the core tracking stations of the International Laser Ranging Service (ILRS). The main limitation to achieving a similar level of range accuracy is the presence of uncorrected systematic errors, which can be attributed to various sources at the stations (e.g., calibration and/or synchronization procedures, hardware malfunctioning, nonlinearities in the time-of-flight measurement devices), as well as to modeling deficiencies, especially in the ability to refer the range measurements to the center of mass of the spacecraft. The ILRS has always been active in adopting rigorous procedures to detect and remove systematic errors from the data: a group of ILRS analysis centers routinely performs data quality control a few hours after data acquisition; the ILRS Analysis Standing Committee (ASC) is in charge of long-term monitoring and characterization of systematic errors in the observations used for the ILRS products; a Quality Control Board was established in 2015 to address SLR systems’ biases and other data issues. In particular, the ASC is devoting efforts on an investigation of an alternative approach whereby a simultaneous estimation of site coordinates and range biases provides station positions that are in principle free of systematic errors. Results using this approach have shown a significant impact on the realization of the TRF, in particular by reducing the existing scale offset between the VLBI and SLR solutions and reaching a closer agreement with the ITRF2014 scale. This paper outlines the work that continues to be done to improve these products and in particular focuses on new research to evaluate rigorously any impact on the strength of coordinate solutions and geophysical inferences when systematic range errors are determined simultaneously with reference frame parameters. Future procedures for handling systematic errors will be informed by the outcome of the current investigations. Numéro de notice : A2019-612 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-019-01319-w date de publication en ligne : 19/11/2019 En ligne : https://doi.org/10.1007/s00190-019-01319-w Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94800 [article]

Troposphere delay modeling with horizontal gradients for satellite laser ranging / M. Drożdżewski in Journal of geodesy, vol 93 n°10 (October 2019)  

Public [article]  inJournal of geodesy > vol 93 n°10 (October 2019) Titre : Troposphere delay modeling with horizontal gradients for satellite laser ranging Type de document : Article/Communication Auteurs : M. Drożdżewski, Auteur ; Krzysztof Sosnica, Auteur ; Florian Zus, Auteur ; Kyriakos Balidakis, Auteur Année de publication : 2019 Note générale : bibbliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] angle vertical [Termes descripteurs IGN] coordonnées polaires [Termes descripteurs IGN] dissymétrie [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] géocentre [Termes descripteurs IGN] gradient de troposphère [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] Lageos [Termes descripteurs IGN] retard troposphérique [Termes descripteurs IGN] Sentinel-3 [Termes descripteurs IGN] station TLS (télémétrie) [Termes descripteurs IGN] télémètre laser sur satellite Résumé : (auteur) Satellite laser ranging (SLR) constitutes a fundamental space geodetic technique providing global geodetic parameters, such as geocenter coordinates, Earth rotation parameters, and low-degree gravity field coefficients. The tropospheric delay correction is one of the crucial corrections that have to be taken into account when processing SLR data. Current conventional models of the troposphere delays assume a full symmetry of the atmosphere above SLR stations. Neglecting horizontal gradients in SLR solutions introduces a systematic error in SLR products, especially for the observations at low elevation angles, and leads to a deterioration of the consistency between SLR and other space geodetic techniques, such as global navigational satellite systems and very-long-baseline interferometry. We derive new mapping function coefficients, as well as first- and second-order horizontal gradients, all of which are based on numerical weather models, in order to properly consider the azimuthal asymmetry in SLR solutions. We test the enhanced mapping function and horizontal gradients on the solutions based on 11 years of SLR observations to LAGEOS-1/2 satellites and 1 year of SLR observations to Sentinel-3A. The consideration of azimuthal asymmetry of the atmosphere above the SLR stations has a systematic effect on SLR-derived products, such as station and geocenter coordinates and pole coordinates. Horizontal gradients in SLR solutions improve the consistency between SLR-derived pole coordinates and the combined IERS-C04 series by means of reducing the offset for the X and Y pole coordinates by 20 μas. The second-order horizontal gradients are negligible in SLR solutions; thus, including first-order gradients is sufficient for SLR solutions. Numéro de notice : A2019-607 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-019-01287-1 date de publication en ligne : 22/08/2019 En ligne : https://doi.org/10.1007/s00190-019-01287-1 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94790 [article]

Modeling the VLBI delay for Earth satellites / Frédéric Jaron in Journal of geodesy, vol 93 n°7 (July 2019)  

Public [article]  inJournal of geodesy > vol 93 n°7 (July 2019) . - pp 953 - 961 Titre : Modeling the VLBI delay for Earth satellites Type de document : Article/Communication Auteurs : Frédéric Jaron, Auteur ; Axel Nothnagel, Auteur Année de publication : 2019 Article en page(s) : pp 953 - 961 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] E-GRASP [Termes descripteurs IGN] Geodetic Reference Antenna in Space [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] point de liaison (géodésie) [Termes descripteurs IGN] poursuite de satellite [Termes descripteurs IGN] propagation du signal [Termes descripteurs IGN] retard troposphérique [Termes descripteurs IGN] système international de référence céleste Résumé : (auteur) Very-long-baseline interferometry (VLBI) observations of satellites orbiting the Earth and emitting an artificial radio signal have the potential of becoming an important technique for improving the frame ties between celestial and terrestrial reference frames. Modeling the delay of the signal reception at one station with respect to the other station of a baseline is a fundamental step for correlation and parameter estimation. The near-field VLBI delay models developed so far include numerical computation, which may become expensive in terms of computation time. This applies especially when partial derivatives are to be computed, which is the normal case for least squares adjustments. Furthermore, all the models are formulated in the barycentric celestial reference system requiring large numbers. Here we present an analytical expression for the VLBI delay for the special case of satellites orbiting the Earth, observed by ground-based radio telescopes. We analytically solve the light time equation for each signal propagation path from the source to receiver one and to receiver two under the simplification of linearizing the trajectory of the satellite. By approximating the motion of the Earth as uniform during the short signal travel times we are able to work in the geocentric celestial reference system. We investigate differences between numerical and analytical solutions by simulating VLBI observations of Earth satellites. These tests reveal that delays computed with the analytical formula are consistent with those computed with the numerical solution below the detection level of VLBI but at less computational cost. Numéro de notice : A2019-354 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-018-1217-0 date de publication en ligne : 20/11/2018 En ligne : https://doi.org/10.1007/s00190-018-1217-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93408 [article]

Least-squares cross-wavelet analysis and its applications in geophysical time series / Ebrahim Ghaderpour in Journal of geodesy, vol 92 n° 10 (October 2018)  

Public [article]  inJournal of geodesy > vol 92 n° 10 (October 2018) . - pp 1223 - 1236 Titre : Least-squares cross-wavelet analysis and its applications in geophysical time series Type de document : Article/Communication Auteurs : Ebrahim Ghaderpour, Auteur ; Elmas Sinem Ince, Auteur ; Spiros D. Pagiatakis, Auteur Année de publication : 2018 Article en page(s) : pp 1223 - 1236 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] champ de pesanteur terrestre [Termes descripteurs IGN] données GOCE [Termes descripteurs IGN] données ITGB [Termes descripteurs IGN] gradient de gravitation [Termes descripteurs IGN] matrice de covariance [Termes descripteurs IGN] méthode des moindres carrés [Termes descripteurs IGN] série temporelle [Termes descripteurs IGN] transformation en ondelettes Résumé : (Auteur) The least-squares wavelet analysis, an alternative to the classical wavelet analysis, was introduced in order to analyze unequally spaced and non-stationary time series exhibiting components with variable amplitude and frequency over time. There are a few methods such as cross-wavelet transform and wavelet coherence that can analyze two time series together. However, these methods cannot generally be used to analyze unequally spaced and non-stationary time series with associated covariance matrices that may have trends and/or datum shifts. A new method of analyzing two time series together, namely the least-squares cross-wavelet analysis, is developed and applied to study the disturbances in the gravitational gradients observed by GOCE satellite that arise from plasma flow in the ionosphere represented by Poynting flux. The proposed method also shows its outstanding performance on the Westford–Wettzell very long baseline interferometry baseline length and temperature series. Numéro de notice : A2018-462 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-018-1156-9 date de publication en ligne : 26/05/2018 En ligne : https://doi.org/10.1007/s00190-018-1156-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91061 [article]

Geodetic VLBI with an artificial radio source on the Moon : a simulation study / Grzegorz Klopotek in Journal of geodesy, vol 92 n° 5 (May 2018)  

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Basic Earth's Parameters as estimated from VLBI observations / Ping Zhu in Geodesy and Geodynamics, vol 8 n° 6 (November 2017)  

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Application of ray-traced tropospheric slant delays to geodetic VLBI analysis / Armin Hofmeister in Journal of geodesy, vol 91 n° 8 (August 2017)  

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A global terrestrial reference frame from simulated VLBI and SLR data in view of GGOS / Susanne Glaser in Journal of geodesy, vol 91 n° 7 (July 2017)  

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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)  

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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)  

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On the consistency of the current conventional EOP series and the celestial and terrestrial reference frames / Santiago Belda in Journal of geodesy, vol 91 n° 2 (February 2017)  

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IERS annual report 2015 / Wolfgang R. Dick (2017)  

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Complex demodulation in monitoring earth rotation by VLBI: testing the algorithm by analysis of long periodic EOP components / Agata Wielgosz in Artificial satellites, vol 51 n° 4 (December 2016)  

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Determination of a terrestrial reference frame via Kalman filtering of very long baseline interferometry data / Benedikt Soja in Journal of geodesy, vol 90 n° 12 (December 2016)  

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