Détail de l'auteur
Auteur Axel Nothnagel |
Documents disponibles écrits par cet auteur (10)
Ajouter le résultat dans votre panier
Visionner les documents numériques
Affiner la recherche Interroger des sources externesCombinatorial optimization applied to VLBI scheduling / A. Corbin in Journal 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 IGN] analyse combinatoire (maths)
[Termes IGN] données VGOS
[Termes IGN] interférométrie à très grande base
[Termes IGN] positionnement par ITGB
[Termes IGN] programmation linéaire
[Termes IGN] retard troposphérique zénithal
[Termes IGN] station VLBI
[Termes IGN] téléscope
[Termes IGN] temps universel coordonnéRésumé : (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 Affiliation des auteurs : non IGN 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
in Journal of geodesy > vol 94 n°2 (February 2020)[article]
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 IGN] E-GRASP
[Termes IGN] Geodetic Reference Antenna in Space
[Termes IGN] interférométrie à très grande base
[Termes IGN] point de liaison (géodésie)
[Termes IGN] poursuite de satellite
[Termes IGN] propagation du signal
[Termes IGN] retard troposphérique
[Termes IGN] système international de référence célesteRésumé : (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 Affiliation des auteurs : non IGN 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
in Journal of geodesy > vol 93 n°7 (July 2019) . - pp 953 - 961[article]
Titre : Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning Type de document : Article/Communication Auteurs : Christoph Holst, Auteur ; Axel Nothnagel, Auteur ; Martin Blome, Auteur ; et al., Auteur Année de publication : 2015 Article en page(s) : pp 1 - 14 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Lasergrammétrie
[Termes IGN] auto-étalonnage
[Termes IGN] déformation d'édifice
[Termes IGN] données lidar
[Termes IGN] données localisées 3D
[Termes IGN] radiotélescope
[Termes IGN] segmentation
[Termes IGN] semis de pointsRésumé : (auteur) The main reflectors of radio telescopes deform due to gravitation when changing their elevation angle. This can be analyzed by scanning the paraboloid surface with a terrestrial laser scanner and by determining focal length variations and local deformations from best-fit approximations.
For the Effelsberg radiotelescope, both groups of deformations are estimated from seven points clouds measured at different elevation angles of the telescope: the focal length decreases by 22.7 mm when tilting the telescope from 90 deg to 7.5 deg elevation angle. Variable deformations of ± 2 mm are detected as well at certain areas. Furthermore, a few surface panels seem to be misaligned.
Apart from these results, the present study highlights the need for an appropriate measurement concept and for preprocessing stepswhen using laser scanners for area-based deformation analyses. Especially, data reduction, object segmentation and laser scanner calibration are discussed in more detail. An omission of these steps would significantly degrade the deformation analysis and the significance of its results. This holds for all sorts of laser scanner based analyses.Numéro de notice : A2015-026 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2014-0018 En ligne : http://www.degruyter.com/view/j/jag.2015.9.issue-1/jag-2014-0018/jag-2014-0018.x [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76879
in Journal of applied geodesy > vol 9 n° 1 (March 2015) . - pp 1 - 14[article]
Titre : Resolution on the nomenclature of space geodetic reference points and local tie measurements Type de document : Article/Communication Auteurs : Sten Bergstrand, Auteur ; Xavier Collilieux Editeur : [s.l.] : [s.n.] Année de publication : nov 2014 Conférence : REFAG 2014, Reference Frames for Applications in Geosciences (IAG 2014 - Commission 1 symposium) 13/10/2014 17/10/2014 Kirchberg Grand Duché du Luxembourg Proceedings Springer Importance : 4 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] point de liaison (géodésie)
[Termes IGN] point de repère
[Termes IGN] terminologieRésumé : (auteur) We establish a specific but general terminology in order to clarify discussions on topics related to local tie measurements. The terminology meets the requirements of an observing system that encompasses existing International Earth Rotation and Reference Systems Service (IERS) techniques as well as other observation techniques of the Global Geodetic Observing System (GGOS). Numéro de notice : C2014-031 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : sans En ligne : https://www.iers.org/SharedDocs/Publikationen/EN/IERS/WorkingGroups/SiteSurvey/B [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83276 Documents numériques
en open access
Resolution on the nomenclature ... - pdf auteurAdobe Acrobat PDFvol 85 n° 7 - July 2011 - CONT08 -continuous geodetic VLBI campaign 2008 August 12-26 2008 (Bulletin de Journal of geodesy) / Axel Nothnagel
Titre : vol 85 n° 7 - July 2011 - CONT08 -continuous geodetic VLBI campaign 2008 August 12-26 2008 Type de document : Périodique Auteurs : Axel Nothnagel, Éditeur scientifique ; U. Hungentobler, Éditeur scientifique ; International association of geodesy, Auteur ; David A. Salstein, Éditeur scientifique Année de publication : 2011 Importance : 50 p. Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] dégradation du signal
[Termes IGN] interférométrie à très grande base
[Termes IGN] troposphèreNuméro de notice : 266-201107 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Numéro de périodique En ligne : http://link.springer.com/journal/190/85/7/page/1 Format de la ressource électronique : URL sommaire Permalink : https://documentation.ensg.eu/index.php?lvl=bulletin_display&id=16338 [n° ou bulletin]
- VLBI-derived troposphere parameters during CONT08 / Robert Heinkelmann in Journal of geodesy, vol 85 n° 7 (July 2011)
- Multi-technique comparison of troposphere zenith delays and gradients during CONT08 / Kamil Teke in Journal of geodesy, vol 85 n° 7 (July 2011)
- High-resolution atmospheric angular momentum functions related to Earth rotation parameters during CONT08 / Daniel Gambis in Journal of geodesy, vol 85 n° 7 (July 2011)
Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 266-2011071 RAB Revue Centre de documentation En réserve L003 Disponible Space-time reference systems for monitoring global change and for precise navigation / Axel Nothnagel (2010)
PermalinkPermalinkPermalinkProceedings of the 9th working meeting on European VLBI for Geodesy and Astrometry / J. Campbell (1993)
PermalinkRadiointerferometrische Beobachtungen zur Bestimmung der Polbewegung unter Benutzung langer Nord-Süd-Basislinien / Axel Nothnagel (1991)
Permalink
