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Optimizing a network-based RTK method for OTF [on-the-fly] positioning / L.P. Fortes in GPS solutions, vol 7 n° 2 (August 2003)  

Public [article]  inGPS solutions > vol 7 n° 2 (August 2003) . - pp 61 - 73 Titre : Optimizing a network-based RTK method for OTF [on-the-fly] positioning Type de document : Article/Communication Auteurs : L.P. Fortes, Auteur ; M.E. Cannon, Auteur ; et al., Auteur Année de publication : 2003 Article en page(s) : pp 61 - 73 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] covariance [Termes IGN] erreur [Termes IGN] filtre de Kalman [Termes IGN] ionosphère [Termes IGN] méthode des moindres carrés [Termes IGN] optimisation (mathématiques) [Termes IGN] orbite [Termes IGN] positionnement cinématique en temps réel [Termes IGN] précision centimétrique [Termes IGN] résolution d'ambiguïté [Termes IGN] station de référence [Termes IGN] valeur efficace Résumé : (Auteur) Differential GPS is able to provide cm-level positoning accuracies, as long as the carrier phase ambiguities are resolved to integer values. Classical methods are based on the use of a single reference station located in the vicinity of the rover. Due to the spatial decorrelation of the errors, the distance between the reference station and the user is generally limited to within 20-30 km or even less, mainly due to the ionosphere. The MultiRef method, developed at the University of Calgary, uses a network of reference stations to generate regional code and carrier phase corrections, which can be transmitted to users in order to increase the distance over which integer ambiguity resolution is possible. In the original method, the correlated errors, due to the satellite orbits, troposphere, and ionosphere are modeled together using the L1 and wide-lane observables. In this paper extensive efforts were carried out towards as optimizing the MultiRef method with the objective of maximizing its performance. Data collected in southeastern Brazil was used in this research. At first, the impact of using covariance function calculated with different data sets was assessed, showing improvement variations of up to 14% in the observation domain compared to using no network corrections, with the exact improvement depending on the data set used in the computation. A new approach, also using least-squares prediction (collation), was proposed to separately model the correlated errors. An additional effort was carried out in the terms of modeling the ionosphere into directional components. Results of the enhanced method showed the same level of improvement as those obtained using the original covariance functions. However, this new approach has advantages with respect to the transmission of the corrections. Finally, an additional step was taken in terms of applying a Kalman filter to the corrections in order to improve their quality. For cases when the corresponding satellite was setting at low elevations, the filter approach improved results up to 44%. A study on the impact of the various covariance functions on the estimated accuracy of the corrections is also included. Numéro de notice : A2003-370 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-003-0054-6 En ligne : https://doi.org/10.1007/s10291-003-0054-6 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26450 [article]

Degradation of GPS performance in geomagnetically disturbed conditions / E.L. Afraimovitch in GPS solutions, vol 7 n° 2 (August 2003)  

Public [article]  inGPS solutions > vol 7 n° 2 (August 2003) . - pp 109 - 119 Titre : Degradation of GPS performance in geomagnetically disturbed conditions Type de document : Article/Communication Auteurs : E.L. Afraimovitch, Auteur ; V.V. Demyanov, Auteur Année de publication : 2003 Article en page(s) : pp 109 - 119 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] analyse comparative [Termes IGN] géomagnétisme [Termes IGN] instrumentation Ashtech [Termes IGN] instrumentation Trimble [Termes IGN] perturbation [Termes IGN] récepteur GPS [Termes IGN] signal GPS [Termes IGN] tempête magnétique Résumé : (Auteur) During geomagnetically disturbed conditions, the accuracy and quality of GPS performance is impaired. Unlike geomagnetically quiet conditions, magnetic storm conditions are accompanied by an increase in the spherical standard deviation of the position determination, for all types of GPS receivers. In magnetic storm conditions there is an increase in the number of slips of the one-frequency mode of coordinate determination. We have identified an unambiguous tendency of the slip density of the one-frequency mode to increase for the ASHTECH and TRIMBLE GPS receivers. For the AOA receivers this tendency was not observed in any of the cases considered. The slip density in the two-frequency mode of coordinate determination in magnetic storm conditions increases most dramatically for the ASHTECH receivers. Regarding the TRIMBLE receivers, there is a similar, but less clearly pronounced, picture. No slips of the two-frequency mode were detected for the AOA receivers in the cases under consideration. Numéro de notice : A2003-371 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-003-0053-7 En ligne : https://doi.org/10.1007/s10291-003-0053-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26451 [article]