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Ionospheric effects in uncalibrated phase delay estimation and ambiguity-fixed PPP based on raw observable model / Shengfeng Gu in Journal of geodesy, vol 89 n° 5 (May 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 5 (May 2015) . - pp 447 - 457 Titre : Ionospheric effects in uncalibrated phase delay estimation and ambiguity-fixed PPP based on raw observable model Type de document : Article/Communication Auteurs : Shengfeng Gu, Auteur ; Chuang Shi, Auteur ; Yidong Lou, Auteur ; Jingnan Liu, Auteur Année de publication : 2015 Article en page(s) : pp 447 - 457 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] correction ionosphérique [Termes IGN] modèle ionosphérique [Termes IGN] positionnement cinématique en temps réel [Termes IGN] positionnement ponctuel précis [Termes IGN] propagation ionosphérique [Termes IGN] résolution d'ambiguïté [Termes IGN] retard ionosphèrique [Termes IGN] signal GNSS [Termes IGN] teneur totale en électrons Résumé : (auteur) Zero-difference (ZD) ambiguity resolution (AR) reveals the potential to further improve the performance of precise point positioning (PPP). Traditionally, PPP AR is achieved by Melbourne–Wübbena and ionosphere-free combinations in which the ionosphere effect are removed. To exploit the ionosphere characteristics, PPP AR with L1 and L2 raw observable has also been developed recently. In this study, we apply this new approach in uncalibrated phase delay (UPD) generation and ZD AR and compare it with the traditional model. The raw observable processing strategy treats each ionosphere delay as an unknown parameter. In this manner, both a priori ionosphere correction model and its spatio-temporal correlation can be employed as constraints to improve the ambiguity resolution. However, theoretical analysis indicates that for the wide-lane (WL) UPD retrieved from L1/L2 ambiguities to benefit from this raw observable approach, high precision ionosphere correction of better than 0.7 total electron content unit (TECU) is essential. This conclusion is then confirmed with over 1 year data collected at about 360 stations. Firstly, both global and regional ionosphere model were generated and evaluated, the results of which demonstrated that, for large-scale ionosphere modeling, only an accuracy of 3.9 TECU can be achieved on average for the vertical delays, and this accuracy can be improved to about 0.64 TECU when dense network is involved. Based on these ionosphere products, WL/narrow-lane (NL) UPDs are then extracted with the raw observable model. The NL ambiguity reveals a better stability and consistency compared to traditional approach. Nonetheless, the WL ambiguity can be hardly improved even constrained with the high spatio-temporal resolution ionospheric corrections. By applying both these approaches in PPP-RTK, it is interesting to find that the traditional model is more efficient in AR as evidenced by the shorter time to first fix, while the three-dimensional positioning accuracy of the RAW model outperforms the combination model by about 7.9%. This reveals that, with the current ionosphere models, there is actually no optimal strategy for the dual-frequency ZD ambiguity resolution, and the combination approach and raw approach each has merits and demerits. Numéro de notice : A2015-345 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0789-1 Date de publication en ligne : 15/02/2015 En ligne : https://doi.org/10.1007/s00190-015-0789-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76717 [article]

Analysis of orbital configurations for geocenter determination with GPS and low-Earth orbiters / Da Kuang in Journal of geodesy, vol 89 n° 5 (May 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 5 (May 2015) . - pp 471 - 481 Titre : Analysis of orbital configurations for geocenter determination with GPS and low-Earth orbiters Type de document : Article/Communication Auteurs : Da Kuang, Auteur ; Yoaz E. Bar-Sever, Auteur ; Bruce J. Haines, Auteur Année de publication : 2015 Article en page(s) : pp 471 - 481 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse comparative [Termes IGN] antenne GPS [Termes IGN] double différence [Termes IGN] géocentre [Termes IGN] hauteur ellipsoïdale [Termes IGN] orbite basse [Termes IGN] orbitographie par GNSS [Termes IGN] poursuite de satellite [Termes IGN] récepteur GPS [Termes IGN] télémétrie laser sur satellite Résumé : (auteur) We use a series of simulated scenarios to characterize the observability of geocenter location with GPS tracking data. We examine in particular the improvement realized when a GPS receiver in low Earth orbit (LEO) augments the ground network. Various orbital configurations for the LEO are considered and the observability of geocenter location based on GPS tracking is compared to that based on satellite laser ranging (SLR). The distance between a satellite and a ground tracking-site is the primary measurement, and Earth rotation plays important role in determining the geocenter location. Compared to SLR, which directly and unambiguously measures this distance, terrestrial GPS observations provide a weaker (relative) measurement for geocenter location determination. The estimation of GPS transmitter and receiver clock errors, which is equivalent to double differencing four simultaneous range measurements, removes much of this absolute distance information. We show that when ground GPS tracking data are augmented with precise measurements from a GPS receiver onboard a LEO satellite, the sensitivity of the data to geocenter location increases by more than a factor of two for Z-component. The geometric diversity underlying the varying baselines between the LEO and ground stations promotes improved global observability, and renders the GPS technique comparable to SLR in terms of information content for geocenter location determination. We assess a variety of LEO orbital configurations, including the proposed orbit for the geodetic reference antenna in space mission concept. The results suggest that a retrograde LEO with altitude near 3,000 km is favorable for geocenter determination. Numéro de notice : A2015-347 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0792-6 Date de publication en ligne : 08/02/2015 En ligne : https://doi.org/10.1007/s00190-015-0792-6 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76721 [article]

Minimal detectable outliers as measures of reliability / Karl Rudolf Koch in Journal of geodesy, vol 89 n° 5 (May 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 5 (May 2015) . - pp 483-490 Titre : Minimal detectable outliers as measures of reliability Type de document : Article/Communication Auteurs : Karl Rudolf Koch, Auteur Année de publication : 2015 Article en page(s) : pp 483-490 Note générale : Bibliographe Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie [Termes IGN] B-Spline [Termes IGN] erreur systématique [Termes IGN] fiabilité des données [Termes IGN] méthode de Monte-Carlo [Termes IGN] réseau géodésique [Termes IGN] valeur aberrante Résumé : (auteur) The concept of reliability was introduced into geodesy by Baarda (A testing procedure for use in geodetic networks. Publications on Geodesy, vol. 2. Netherlands Geodetic Commission, Delft, 1968). It gives a measure for the ability of a parameter estimation to detect outliers and leads in case of one outlier to the MDB, the minimal detectable bias or outlier. The MDB depends on the non-centrality parameter of the χ2-distribution, as the variance factor of the linear model is assumed to be known, on the size of the outlier test of an individual observation which is set to 0.001 and on the power of the test which is generally chosen to be 0.80. Starting from an estimated variance factor, the F-distribution is applied here. Furthermore, the size of the test of the individual observation is a function of the number of outliers to keep the size of the test of all observations constant, say 0.05. The power of the test is set to 0.80. The MDBs for multiple outliers are derived here under these assumptions. The method is applied to the reconstruction of a bell-shaped surface measured by a laser scanner. The MDBs are introduced as outliers for the alternative hypotheses of the outlier tests. A Monte Carlo method reveals that due to the way of introducing the outliers, the false null hypotheses cannot be rejected on the average with a power of 0.80 if the MDBs are not enlarged by a factor. Numéro de notice : A2015-348 Affiliation des auteurs : non IGN Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0793-5 Date de publication en ligne : 12/02/2015 En ligne : https://doi.org/10.1007/s00190-015-0793-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76722 [article]

Eliminating diffraction effects during multi-frequency correction in global navigation satellite systems / M.V. Tinin in Journal of geodesy, vol 89 n° 5 (May 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 5 (May 2015) . - pp 491 - 503 Titre : Eliminating diffraction effects during multi-frequency correction in global navigation satellite systems Type de document : Article/Communication Auteurs : M.V. Tinin, Auteur Année de publication : 2015 Article en page(s) : pp 491 - 503 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] correction du signal [Termes IGN] correction ionosphérique [Termes IGN] diffraction [Termes IGN] positionnement par GPS [Termes IGN] résidu [Termes IGN] signal GNSS [Termes IGN] signal multidimensionnel Résumé : (auteur) In the geometrical optics approximation, the ionospheric part of error in measuring phase and code delays of the satellite signal may be represented as a rapidly decreasing series in inverse power of frequency. Such a simple frequency dependence allows us to use multi-frequency measurements for eliminating the error in such multi-frequency Global Navigation Satellite Systems as GPS, GLONASS, BeiDou, and Galileo. However, the elimination of errors is handicapped by diffraction effects during signal propagation through turbulent ionospheric plasma. The numerical simulation has shown that when using the spatial processing in the form of Fresnel inversion the transition from dual-frequency to triple-frequency measurements reduces the average error of measurement. Yet fluctuations of the error diminish only if the inner scale exceeds the Fresnel radius. In the opposite case of excess of the Fresnel radius over the inner scale, the random component of the residual error is growing during the transition to triple-frequency measurements. The numerical simulation results also suggest that the Fresnel spatial processing in dual-frequency measurements at the optimal distance to the virtual screen can reduce the average error from centimeter to submillimeter level, which renders the transition to triple-frequency measurements unnecessary. The study of the residual error dependence on the distance from the virtual screen to the observer has revealed that the optimum value of this distance may be found from the minimum condition of amplitude scintillation index of the processed signal. The signal thus processed may be utilized both in geodetic precise measurements and in diagnostics of the lower atmosphere. Numéro de notice : A2015-349 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0794-4 En ligne : https://doi.org/10.1007/s00190-015-0794-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76723 [article]