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Static GNSS precise point positioning using free online services for Africa / Anis Abdallah in Survey review, vol 48 n° 346 (January 2016)  

Public [article]  inSurvey review > vol 48 n° 346 (January 2016) . - pp. 61 - 77 Titre : Static GNSS precise point positioning using free online services for Africa Type de document : Article/Communication Auteurs : Anis Abdallah, Auteur ; B. V. Schwieger, Auteur Année de publication : 2016 Article en page(s) : pp. 61 - 77 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] Afrique (géographie politique) [Termes IGN] positionnement par GNSS [Termes IGN] positionnement ponctuel précis [Termes IGN] positionnement statique [Termes IGN] retard troposphérique zénithal [Termes IGN] service fondé sur la position [Termes IGN] station GNSS Résumé : (auteur) The GNSS precise point positioning (PPP) technique has been extensively covered in recent research. In this study, six International global navigation satellite system (GNSS) Service (IGS) stations defined by 4-digits code in Africa were selected to be processed. The stations cover different climates in Africa. HARB, SUTH and WIND stations cover the mid-latitude area and NKLG, NURK and MAL2 are located in the equatorial region. Two data sessions were selected in processing to cover the winter and summer seasons: the first session of 3 days [01–03 January 2013 (DOY: 001–003/2013)] and the second session of 3 days [01–03 July 2013 (DOY: 182–184/2013)]. This paper aims to evaluate the accuracy of static PPP coordinate solution in Africa for different convergence times using free online services: Canadian Spatial Reference System (CSRS)-PPP, Automatic Precise Point Service (APPS)-PPP and GPS Analysis and Positioning Software (GAPS)-PPP. The stations’ observation times were divided into different observation times (1, 2, 4, 8, 12, and 24 h).The PPP coordinate solution was compared to the reference solution of those stations. The investigation is continued by estimating the PPP total tropospheric zenith delay (TZD) parameters, which were obtained by the different online services. These parameters were compared to the published parameters from IGS. The comparison between the different online services shows that the CSRS-PPP provides the best solution after 4 and 8 h. The APPS-PPP and CSRS-PPP provides the same solution in millimeters level after 12 h. In the equatorial region, the PPP coordinate solution is significantly improved between 12 and 24 h. Moreover, GAPS-PPP is not recommended to be used in the equatorial stations, where it shows a high error compared to CSRS-PPP and APPS-PPP even after 24 h. The mid-latitude stations show a better PPP coordinate solution in the winter than in the summer, but the equatorial stations present a low accuracy for the two sessions. Regarding the PPP tropospheric delay estimation, an additional station (HNUS) is used in the mid-latitude area, which has a low ellipsoidal height. APPS-PPP shows the best solution in the TZD estimation. The GAPS-PPP online service shows a systemic error in estimation and a high RMS relative to the TZD values known from IGS. The ellipsoidal height for antenna indicates a negative correlation to the estimated tropospheric values, but there is no effect for the variation of the ellipsoidal height in the estimated RMS. The estimated tropospheric parameters are correlated with the PPP coordinate estimation, where the GAPS-PPP service provides the worst PPP coordinate solution and at the same time, it shows the worst accuracy for tropospheric parameters estimation. Moreover, the estimated tropospheric parameters for the mid-latitude stations in the summer season show a higher RMS than in the winter season, which matches the same sequence of the PPP coordinates. The NKLG and NURK stations present a low accuracy for the tropospheric estimation, which is matching to the low accuracy of the PPP coordinates obtained from the different online services. Numéro de notice : A2016-046 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/00396265.2015.1097595 En ligne : https://doi.org/10.1080/00396265.2015.1097595 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79639 [article]

Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries / Anis Abdallah in Nature, vol 282 (1979)  

Public [article]  inNature > vol 282 (1979) . - pp 17 - 23 Titre : Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries Type de document : Article/Communication Auteurs : Anis Abdallah, Auteur ; Vincent Courtillot, Auteur ; Michel Kasser , Auteur ; Anne-Yvonne Le Dain, Auteur ; Jean-Claude Lépine, Auteur ; Bernard Robineau, Auteur ; Jean-Claude Ruegg, Auteur ; Paul Tapponnier, Auteur ; Albert Tarantola, Auteur Année de publication : 1979 Article en page(s) : pp 17 - 23 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géographie mondiale [Termes IGN] déformation de la croute terrestre [Termes IGN] faille géologique [Termes IGN] rift [Termes IGN] séisme [Termes IGN] tectonique des plaques [Termes IGN] Territoire des Afars et des Issas Résumé : (auteur) The seismicity, the horizontal and vertical ground displacements, and the geometry of active faults and fissures during the seismic and volcanic events of November 1978 in Southern Afar are consistent with an accentuation of the pre-existing topography of the Ghoubbet–Asal rift. The zone of sizeable permanent deformation is restricted to several hundred square kilometres. Elastic rebound models seem to explain the observations. The events occurred in the vicinity of the suggested location of the tip of a lithospheric crack which may have been responsible for the progressive opening of the western Gulf of Aden. Numéro de notice : A1979-057 Affiliation des auteurs : IGN+Ext (1940-2011) Thématique : POSITIONNEMENT Nature : Article DOI : 10.1038/282017a0 Date de publication en ligne : 01/11/1979 En ligne : https://doi.org/10.1038/282017a0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=34239 [article]