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On the detectability of mis-modeled biases in the network-derived positioning corrections and their user impact / Amir Khodabandeh in GPS solutions, vol 23 n° 3 (July 2019)  

Public [article]  inGPS solutions > vol 23 n° 3 (July 2019) Titre : On the detectability of mis-modeled biases in the network-derived positioning corrections and their user impact Type de document : Article/Communication Auteurs : Amir Khodabandeh, Auteur ; Jinling Wang, Auteur ; Chris Rizos, Auteur ; Ahmed El-Mowafy, Auteur Année de publication : 2019 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes descripteurs IGN] correction [Termes descripteurs IGN] filtre de Kalman [Termes descripteurs IGN] inférence statistique [Termes descripteurs IGN] intégrité des données [Termes descripteurs IGN] modèle linéaire [Termes descripteurs IGN] positionnement cinématique en temps réel [Termes descripteurs IGN] positionnement par GNSS [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] précision du positionnement [Termes descripteurs IGN] Receiver Autonomous Integrity Monitoring [Termes descripteurs IGN] traitement de données GNSS Résumé : (auteur) High-precision single-receiver positioning requires the provision of reliable network-derived corrections. Care must therefore be exercised to continuously check the quality of the corrections and to detect the possible presence of mis-modeled biases in the network data. In network-RTK or its state-space implementation, PPP-RTK, quality control of the solutions is executed in two separate phases: the network component and the user component. Once confidence in the network-derived solutions is declared, a subset of the solutions is sent as corrections to a single-receiver user, thereby allowing the user to separately check the integrity of his network-aided model. In such a two-step integrity monitoring procedure, an intermediate step is missing, the integrity monitoring of the corrections themselves. It is the goal of this contribution to provide a quality control procedure for GNSS parameter solutions at the correction level, and to measure the impact a missed detection bias has on the (ambiguity-resolved) user position. New detection test statistics are derived with which the single-receiver user can check the overall validity of the corrections even before applying them to his data. A small-scale network of receivers is utilized to provide numerical insights into the detectability of mis-modeled biases using the proposed detectors and to analyze the impact of such biases on the user positioning performance. Numéro de notice : A2019-195 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-019-0863-x date de publication en ligne : 14/05/2019 En ligne : https://doi.org/10.1007/s10291-019-0863-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92649 [article]

Impact of predicting real-time clock corrections during their outages on precise point positioning / Ahmed El-Mowafy in Survey review, vol 51 n° 365 (March 2019)  

Public [article]  inSurvey review > vol 51 n° 365 (March 2019) . - pp 183 - 192 Titre : Impact of predicting real-time clock corrections during their outages on precise point positioning Type de document : Article/Communication Auteurs : Ahmed El-Mowafy, Auteur Année de publication : 2019 Article en page(s) : pp 183 - 192 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] décalage d'horloge [Termes descripteurs IGN] données GNSS [Termes descripteurs IGN] orbite [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] temps réel Résumé : (Auteur) Real-time precise point positioning (RT-PPP) is a popular positioning method for natural hazard warning systems (NHWS) such as for monitoring tsunami and earthquakes. PPP relays on the use of precise orbits and clock corrections. Hence, the positioning accuracy of RT-PPP will significantly deteriorate when experiencing a discontinuity in receiving these corrections, for instance due to a temporary modem failure. The best available approach in this case would be to use the International Global Navigation Satellite Systems Service ultra-rapid (IGU) orbits and clocks that would result in a low positioning accuracy. In this paper, we present a simplified approach to a method that we recently proposed to bridge outages in the corrections and improve the RT-PPP accuracy compared with the use of IGU. In this method, the most recent IGU orbits are used as they are compatible with the RT orbits; however, the clock corrections are predicted as a time series using a linear model with four sinusoidal terms. The prediction errors resulting from this method, age of the model and its validity period are discussed. The impact of using the proposed approach is evaluated at a number of sites of known positions by comparing its performance to using IGU orbits and clocks. Moreover, the impact of using predicted corrections is assessed in different scenarios. The experimental results proved validity of the presented approach where positioning mean RMSE of less than 20 cm was maintained during the outage period. Numéro de notice : A2019-191 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/00396265.2017.1405155 date de publication en ligne : 26/11/2017 En ligne : https://doi.org/10.1080/00396265.2017.1405155 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92635 [article]

Maintaining real-time precise point positioning during outages of orbit and clock corrections / Ahmed El-Mowafy in GPS solutions, vol 21 n° 3 (July 2017)  

Public [article]  inGPS solutions > vol 21 n° 3 (July 2017) . - pp 937 – 947 Titre : Maintaining real-time precise point positioning during outages of orbit and clock corrections Type de document : Article/Communication Auteurs : Ahmed El-Mowafy, Auteur ; Manoj Deo, Auteur ; Nobuaki Kubo, Auteur Année de publication : 2017 Article en page(s) : pp 937 – 947 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] horloge [Termes descripteurs IGN] International GNSS Service [Termes descripteurs IGN] international GPS service for geodynamics [Termes descripteurs IGN] interruption du signal [Termes descripteurs IGN] orbitographie [Termes descripteurs IGN] positionnement cinématique en temps réel [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] précision décimétrique [Termes descripteurs IGN] prévision Résumé : (auteur) The precise point positioning (PPP) is a popular positioning technique that is dependent on the use of precise orbits and clock corrections. One serious problem for real-time PPP applications such as natural hazard early warning systems and hydrographic surveying is when a sudden communication break takes place resulting in a discontinuity in receiving these orbit and clock corrections for a period that may extend from a few minutes to hours. A method is presented to maintain real-time PPP with 3D accuracy less than a decimeter when such a break takes place. We focus on the open-access International GNSS Service (IGS) real-time service (RTS) products and propose predicting the precise orbit and clock corrections as time series. For a short corrections outage of a few minutes, we predict the IGS-RTS orbits using a high-order polynomial, and for longer outages up to 3 h, the most recent IGS ultra-rapid orbits are used. The IGS-RTS clock corrections are predicted using a second-order polynomial and sinusoidal terms. The model parameters are estimated sequentially using a sliding time window such that they are available when needed. The prediction model of the clock correction is built based on the analysis of their properties, including their temporal behavior and stability. Evaluation of the proposed method in static and kinematic testing shows that positioning precision of less than 10 cm can be maintained for up to 2 h after the break. When PPP re-initialization is needed during the break, the solution convergence time increases; however, positioning precision remains less than a decimeter after convergence. Numéro de notice : A2017-442 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-016-0583-4 En ligne : https://doi.org/10.1007/s10291-016-0583-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86360 [article]

Dynamic modeling of GNSS troposphere wet delay for estimation of precipitable water vapour / Ahmed El-Mowafy in Journal of applied geodesy, vol 8 n° 1 (April 2014)  

Public [article]  inJournal of applied geodesy > vol 8 n° 1 (April 2014) . - pp 31 - 42 Titre : Dynamic modeling of GNSS troposphere wet delay for estimation of precipitable water vapour Type de document : Article/Communication Auteurs : Ahmed El-Mowafy, Auteur ; Johnny Lo, Auteur Année de publication : 2014 Article en page(s) : pp 31 - 42 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] autocorrélation [Termes descripteurs IGN] humidité de l'air [Termes descripteurs IGN] modèle dynamique [Termes descripteurs IGN] positionnement par GNSS [Termes descripteurs IGN] précipitation [Termes descripteurs IGN] propagation troposphérique [Termes descripteurs IGN] signal GNSS [Termes descripteurs IGN] vapeur d'eau Résumé : (Auteur) Proper dynamic modelling of the troposphere wet delay using the Global Navigation Satellite Systems (GNSS) measurements is important in precise point positioning and in estimation of the Precipitable Water Vapour (PWV) for weather forecast. The random walk (RW) and the first-order Gauss-Markov (GM) autocorrelation models are commonly used for this purpose. However, it was found that these models consistently underestimate the temporal correlations that exist among the troposphere wet delay. Therefore, a new dynamic model is proposed. The performance of the proposed model in following the autocorrelation of actual data is demonstrated and its impact on the near-real time estimation of the wet delay was tested and compared to that of the GM and RW models. Results showed that the proposed model outperformed these models. When the computed wet delays were used to compute PWV, their estimated valueswere very close to actual PWV data measured by radiosonde with differences less than 1 mm. Numéro de notice : A2014-271 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1515/jag-2013-0012 2 2 total citations on Dimensions. date de publication en ligne : 08/04/2014 En ligne : https://doi.org/10.1515/jag-2013-0012 2 2 total citations on Dimensions. Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=33174 [article]

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The stability of tide gauges in the south Pacific determined from multiepoch geodetic levelling, 1992 to 2010 / Manoj Nilesh Deo in Marine geodesy, vol 36 n° 3 (September - November 2013)  

Public [article]  inMarine geodesy > vol 36 n° 3 (September - November 2013) . - pp 261 - 284 Titre : The stability of tide gauges in the south Pacific determined from multiepoch geodetic levelling, 1992 to 2010 Type de document : Article/Communication Auteurs : Manoj Nilesh Deo, Auteur ; Ramesh Govind, Auteur ; Ahmed El-Mowafy, Auteur Année de publication : 2013 Article en page(s) : pp 261 - 284 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Nivellement [Termes descripteurs IGN] analyse diachronique [Termes descripteurs IGN] Cook (îles) [Termes descripteurs IGN] données marégraphiques [Termes descripteurs IGN] marée océanique [Termes descripteurs IGN] niveau moyen des mers [Termes descripteurs IGN] nivellement par GPS [Termes descripteurs IGN] Pacifique Sud [Termes descripteurs IGN] repère de nivellement [Termes descripteurs IGN] Salomon (îles) [Termes descripteurs IGN] test de performance [Termes descripteurs IGN] Vanuatu Résumé : (Auteur) Tide gauge data is important for determining global or local sea level rise with respect to a global geocentric reference frame. Data from repeated precise levelling connections between the tide gauges and a series of coastal and inland benchmarks, including Continuous GPS (CGPS) benchmarks, are used to determine the stability of tide gauges at 12 locations in the South Pacific. The method for determining this stability is based on a constant velocity model which minimises the net movement amongst a set of datum benchmarks surveyed since the installation of the tide gauges. When assessed at a 95% confidence interval, and with the exception of the Solomon Islands, none of the tide gauges were found to be in motion relative to their CGPS benchmarks. The Solomon Islands estimate is considered to be unreliable since the CGPS benchmark was recently established and has been surveyed fewer than three times. In Tonga and Cook Islands, the tide gauges were found to be disturbed or affected by survey errors whereas the Vanuatu results were affected by earthquakes. Numéro de notice : A2013-711 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490419.2013.786003 date de publication en ligne : 18/03/2016 En ligne : https://doi.org/10.1080/01490419.2013.786003 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32847 [article]

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