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Comparative analysis of real-time precise point positioning zenith total delay estimates / F.A. Ahmed in GPS solutions, vol 20 n° 2 (April 2016)  

Public [article]  inGPS solutions > vol 20 n° 2 (April 2016) . - pp 187 - 199 Titre : Comparative analysis of real-time precise point positioning zenith total delay estimates Type de document : Article/Communication Auteurs : F.A. Ahmed, Auteur ; Pavel Vaclavovic, Auteur ; Felix Norman Teferle, Auteur ; Jan Douša, Auteur ; R.M. Bingley, Auteur ; Denis Laurichesse, Auteur Année de publication : 2016 Article en page(s) : pp 187 - 199 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] analyse comparative [Termes IGN] erreur moyenne [Termes IGN] erreur systématique [Termes IGN] modèle atmosphérique [Termes IGN] positionnement ponctuel précis [Termes IGN] retard troposphérique zénithal [Termes IGN] temps réel [Vedettes matières IGN] Traitement de données GNSS Résumé : (Auteur) The continuous evolution of global navigation satellite systems (GNSS) meteorology has led to an increased use of associated observations for operational modern low-latency numerical weather prediction (NWP) models, which assimilate GNSS-derived zenith total delay (ZTD) estimates. The development of NWP models with faster assimilation cycles, e.g., 1-h assimilation cycle in the rapid update cycle NWP model, has increased the interest of the meteorological community toward sub-hour ZTD estimates. The suitability of real-time ZTD estimates obtained from three different precise point positioning software packages has been assessed by comparing them with the state-of-the-art IGS final troposphere product as well as collocated radiosonde (RS) observations. The ZTD estimates obtained by BNC2.7 show a mean bias of 0.21 cm, and those obtained by the G-Nut/Tefnut software library show a mean bias of 1.09 cm to the IGS final troposphere product. In comparison with the RS-based ZTD, the BNC2.7 solutions show mean biases between 1 and 2 cm, whereas the G-Nut/Tefnut solutions show mean biases between 2 and 3 cm with the RS-based ZTD, and the ambiguity float and ambiguity fixed solutions obtained by PPP-Wizard have mean biases between 6 and 7 cm with the references. The large biases in the time series from PPP-Wizard are due to the fact that this software has been developed for kinematic applications and hence does not apply receiver antenna eccentricity and phase center offset (PCO) corrections on the observations. Application of the eccentricity and PCO corrections to the a priori coordinates has resulted in a 66 % reduction of bias in the PPP-Wizard solutions. The biases are found to be stable over the whole period of the comparison, which are criteria (rather than the magnitude of the bias) for the suitability of ZTD estimates for use in NWP nowcasting. A millimeter-level impact on the ZTD estimates has also been observed in relation to ambiguity resolution. As a result of a comparison with the established user requirements for NWP nowcasting, it was found that both the G-Nut/Tefnut solutions and one of the BNC2.7 solutions meet the threshold requirements, whereas one of the BNC2.7 solution and both the PPP-Wizard solutions currently exceed this threshold. Numéro de notice : A2016-611 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-014-0427-z En ligne : http://dx.doi.org/10.1007/s10291-014-0427-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81810 [article]

Non-linear contouring using crucial ground points / F.A. Ahmed in Survey review, vol 30 n° 231 (01/01/1989)  

Public [article]  inSurvey review > vol 30 n° 231 (01/01/1989) . - pp 15 - 21 Titre : Non-linear contouring using crucial ground points Type de document : Article/Communication Auteurs : F.A. Ahmed, Auteur Année de publication : 1989 Article en page(s) : pp 15 - 21 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Cartographie numérique [Termes IGN] contour [Termes IGN] courbe de niveau [Termes IGN] modèle mathématique [Termes IGN] point d'appui Numéro de notice : A1989-016 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article DOI : 10.1179/sre.1989.30.231.15 En ligne : https://doi.org/10.1179/sre.1989.30.231.15 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=24976 [article]

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