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Impact of GPS antenna phase center models on zenith wet delay and tropospheric gradients / Yohannes Getachew Ejigu in GPS solutions, vol 23 n° 1 (January 2019)  

Public [article]  inGPS solutions > vol 23 n° 1 (January 2019) Titre : Impact of GPS antenna phase center models on zenith wet delay and tropospheric gradients Type de document : Article/Communication Auteurs : Yohannes Getachew Ejigu, Auteur ; Addisu Hunegnaw, Auteur ; Kibrom Ebuy Abraha, Auteur ; et al., Auteur Année de publication : 2019 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] antenne GPS [Termes IGN] centre de phase [Termes IGN] données GPS [Termes IGN] gradient de troposphère [Termes IGN] retard troposphérique zénithal [Termes IGN] teneur intégrée en vapeur d'eau [Vedettes matières IGN] Traitement de données GNSS Résumé : (Auteur) Today Global Navigation Satellite Systems (GNSS) tropospheric products, such as zenith total delays (ZTD) and zenith wet delays (ZWD), are widely used as complementary data sets in numerical weather prediction models. In particular, the wet delays are treated as unknown parameters in GNSS processing and are estimated with other parameters such as station coordinates. In this study, we investigate the effects of Phase Center Correction (PCC) models on ZWD, integrated water vapor (IWV) and horizontal gradients derived from Global Positioning System (GPS) observations. Two solutions were generated using the GAMIT software over the European Reference Frame (EUREF) Permanent GNSS Network (EPN). The first (reference) solution was derived by applying the International GNSS Service (IGS) type-mean PCC models, while for the second solution PCC models from individual calibrations were used. The solutions were generated identically, except for the PCC model differences. The tropospheric products from the two solutions were then compared, with the assumption that common signals would be differenced out. The comparison of the two solutions clearly shows a bias in all tropospheric products, which can be attributed to PCC model deficiencies. Overall, mean biases of 1.8, 0.3, 0.14 and 0.19 mm are evident in ZWD, IWV, North–South and East–West gradients, respectively. Moreover, the differences between the two solutions show seasonal variations. For all antenna types, the ZWD and IWV differences are dominated by white plus power-law noise, with the latter characterizing the low-frequency spectrum. On the other hand, the horizontal gradients exhibit a white plus first-order autoregressive noise characteristic with less than 1% white noise. The individual PCC model provides a better fit to an external independent model in terms of gradient estimates and also provides up to 3% more carrier phase integer ambiguity resolution. Numéro de notice : A2019-056 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-018-0796-9 Date de publication en ligne : 25/10/2018 En ligne : https://doi.org/10.1007/s10291-018-0796-9 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92085 [article]

Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model / Kibrom Ebuy Abraha in GPS solutions, vol 21 n° 1 (January 2017)  

Public [article]  inGPS solutions > vol 21 n° 1 (January 2017) . - pp 89 - 99 Titre : Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model Type de document : Article/Communication Auteurs : Kibrom Ebuy Abraha, Auteur ; Elias Lewi, Auteur ; Frédéric Masson, Auteur ; et al., Auteur Année de publication : 2017 Article en page(s) : pp 89 - 99 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] analyse spatio-temporelle [Termes IGN] données GPS [Termes IGN] Ethiopie [Termes IGN] humidité de l'air [Termes IGN] modèle météorologique [Termes IGN] sécheresse [Termes IGN] station GPS [Termes IGN] teneur en vapeur d'eau [Termes IGN] teneur intégrée en vapeur d'eau [Termes IGN] variation saisonnière Résumé : (Auteur) We characterize the spatial–temporal variability of integrated water vapor (IWV) in Ethiopia from a network of global positioning system (GPS) stations and the European Center for Medium range Weather Forecasting (ECMWF) model. The IWV computed from the ECMWF model is integrated from the height of the GPS stations on 60 pressure levels to take both the actual earth surface and the model orography discrepancies into account. First, we compare the IWV estimated from GPS and from the model. The bias varies from site to site, and the correlation coefficients between the two datasets exceed 0.85 at different time scales. The results of this study show that the general ECMWF IWV trend is underestimation over highlands and overestimation over lowlands for wet periods, and overestimation over highlands and underestimation over lowlands for dry periods with very few exceptional stations. Second, we observe the spatial variation of the IWV. High values are obtained in those stations that are located in the north-eastern (Afar depression) sites and the south-western part of the country. This distribution is related to the spatial variability of the climate in Ethiopia. Finally, we study the seasonal cycle and inter-annual variability of IWV for all stations over Ethiopia. The main result is the strong inter-annual variability observed for the dry seasons. Numéro de notice : A2017-013 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0508-7 En ligne : http://dx.doi.org/10.1007/s10291-015-0508-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83935 [article]