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Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning / Christoph Holst in Journal of applied geodesy, vol 9 n° 1 (March 2015)  

Public [article]  inJournal of applied geodesy > vol 9 n° 1 (March 2015) . - pp 1 - 14 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 points Résumé : (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 [article]

Precise point positioning using multi-constellation GNSS observations for kinematic applications / Mahmoud Abd-El-Rahman in Journal of applied geodesy, vol 9 n° 1 (March 2015)  

Public [article]  inJournal of applied geodesy > vol 9 n° 1 (March 2015) . - pp 15 - 26 Titre : Precise point positioning using multi-constellation GNSS observations for kinematic applications Type de document : Article/Communication Auteurs : Mahmoud Abd-El-Rahman, Auteur ; Ahmed El-Rabbany, Auteur Année de publication : 2015 Article en page(s) : pp 15 - 26 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] erreur systématique [Termes IGN] positionnement cinématique [Termes IGN] positionnement par GNSS [Termes IGN] positionnement ponctuel précis [Termes IGN] simple différence Résumé : (auteur) Traditional precise point positioning (PPP) is commonly based on un-differenced ionosphere-free linear combination of Global Positioning System (GPS) observations. Unfortunately, for kinematic applications, GPS often experiences poor satellite visibility or weak satellite geometry in urban areas. To overcome this limitation, we developed a PPP model, which combines the observations of three global navigation satellite systems (GNSS), namely GPS, GLONASS and Galileo. Both un-differenced and between-satellite single-difference (BSSD) ionosphere-free linear combinations of pseudorange and carrier phase GNSS measurements are processed. The performance of the combined GNSS PPP solution is compared with the GPS-only PPP solution using a real test scenario in downtown Kingston, Ontario. Inter-system biases between GPS and the other two systems are also studied and obtained as a byproduct of the PPP solution. It is shown that the addition of GLONASS observations improves the kinematic PPP solution accuracy in comparison with that of GPS-only solution. However, the contribution of adding Galileo observations is not significant due to the limited number of Galileo satellites launched up to date. In addition, BSSD solution is found to be superior to that of traditional un-differenced model. Numéro de notice : A2015-027 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2014-0021 En ligne : http://www.degruyter.com/view/j/jag.2015.9.issue-1/jag-2014-0021/jag-2014-0021.x [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76880 [article]

An innovative dual frequency PPP model for combined GPS/Galileo observations / Akram Afifi in Journal of applied geodesy, vol 9 n° 1 (March 2015)  

Public [article]  inJournal of applied geodesy > vol 9 n° 1 (March 2015) . - pp 27 - 34 Titre : An innovative dual frequency PPP model for combined GPS/Galileo observations Type de document : Article/Communication Auteurs : Akram Afifi, Auteur ; Ahmed El-Rabbany, Auteur Année de publication : 2015 Article en page(s) : pp 27 - 34 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] positionnement par GNSS [Termes IGN] positionnement ponctuel précis [Termes IGN] précision du positionnement Résumé : (auteur) This paper develops a new dual-frequency precise point positioning model, which combines GPS and Galileo observables. The addition of Galileo satellite system offers more visible satellites to the user, which is expected to enhance the satellite geometry and the overall PPP solution in comparison with GPS-only PPP solution. However, combining GPS and Galileo observables introduces additional biases, which require rigorous modelling, including the GPS to Galileo time offset, and Galileo satellite hardware delay. In this research, a GPS/Galileo ionosphere-free linear combination PPP model is developed. The additional biases of the GPS/Galileo combination are lumped and accounted for through the introduction of a new unknown parameter, inter-systems bias, in the PPP mathematical model. It is shown that a subdecimeter positioning accuracy level and 25% reduction in the solution convergence time can be achieved with the developed GPS/Galileo PPP model. Numéro de notice : A2015-573 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : doi.org/10.1515/jag-2014-0009 En ligne : http://www.degruyter.com/view/j/jag.2015.9.issue-1/jag-2014-0009/jag-2014-0009.x [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76881 [article]