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Performance of Galileo precise time and frequency transfer models using quad-frequency carrier phase observations / Pengfei Zhang in GPS solutions, vol 24 n° 2 (April 2020)  

Public [article]  inGPS solutions > vol 24 n° 2 (April 2020) Titre : Performance of Galileo precise time and frequency transfer models using quad-frequency carrier phase observations Type de document : Article/Communication Auteurs : Pengfei Zhang, Auteur ; Rui Tu, Auteur ; Yuping Gao, Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] bruit atmosphérique [Termes IGN] décalage d'horloge [Termes IGN] erreur systématique interfréquence d'horloge [Termes IGN] fréquence multiple [Termes IGN] modèle mathématique [Termes IGN] phase [Termes IGN] positionnement ponctuel précis [Termes IGN] signal BeiDou [Termes IGN] signal Galileo [Termes IGN] signal GLONASS [Termes IGN] signal GNSS [Termes IGN] signal GPS [Termes IGN] temps-fréquence [Termes IGN] transmission de données Résumé : (auteur) GNSSs, such as Galileo and modernized GPS, BeiDou and GLONASS systems, offer new potential and challenges in precise time and frequency transfer using multi-frequency observations. We focus on the performance of Galileo time and frequency transfer using the E1, E5a, E5b and E5 observations. Dual-frequency, triple-frequency and quad-frequency models for precise time and frequency transfer with different Galileo observations are proposed. Four time and transfer links between international time laboratories are used to assess the performances of different models in terms of time link noise level and frequency stability indicators. The average RMS values of the smoothed residuals of the clock difference series are 0.033 ns, 0.033 ns and 0.034 ns for the dual-frequency, triple-frequency and quad-frequency models with four time links, respectively. With respect to frequency stability, the average stability values at 15,360 s are 9.51 × 10−15, 9.46 × 10−15 and 9.37 × 10−15 for the dual-frequency, triple-frequency and quad-frequency models with four time links, respectively. Moreover, although biases among different models and receiver the inter-frequency exist, their characteristics are relatively stable. Generally, the dual-/triple-/quad-frequency models show similar performance for those time links, and the quad-frequency models can provide significant potential for switching among and unifying the three multi-frequency solutions, as well as further enhancing the redundancy and reliability compared to the current dual-frequency time transfer method. Numéro de notice : A2020-083 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-020-0955-7 Date de publication en ligne : 04/02/2020 En ligne : https://doi.org/10.1007/s10291-020-0955-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94652 [article]

Aggregate keyword nearest neighbor queries on road networks / Pengfei Zhang in Geoinformatica, vol 22 n° 2 (April 2018)  

Public [article]  inGeoinformatica > vol 22 n° 2 (April 2018) . - pp 237 - 268 Titre : Aggregate keyword nearest neighbor queries on road networks Type de document : Article/Communication Auteurs : Pengfei Zhang, Auteur ; Huaizhong Lin, Auteur ; Yunjun Gao, Auteur ; Dongming Lu, Auteur Année de publication : 2018 Article en page(s) : pp 237 - 268 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes d'information géographique [Termes IGN] langage naturel (informatique) [Termes IGN] plus proche voisin, algorithme du [Termes IGN] point d'intérêt [Termes IGN] requête spatiale [Termes IGN] réseau routier [Termes IGN] système d'information géographique Résumé : (Auteur) Given a group Q of query points and a set P of points of interest (POIs), aggregate nearest neighbor (ANN) queries find a POI p from P that achieves the smallest aggregate distance. Specifically, the aggregate distance is defined over the set of distances between p and all query points in Q$\mathcal {Q}$. Existing studies on ANN query mainly consider the spatial proximity, whereas the textual similarity has received considerable attention recently. In this work, we utilize user-specified query keywords to capture textual similarity. We study the aggregate keyword nearest neighbor (AKNN) queries, finding the POI that has the smallest aggregate distance and covers all query keywords. Nevertheless, existing methods on ANN query are either inapplicable or inefficient when applied to the AKNN query. To answer our query efficiently, we first develop a dual-granularity (DG) indexing schema. It preserves abstracts of the road network by a tree structure, and preserves detailed network information by an extended adjacency list. Then, we propose a minimal first search (MFS) algorithm. It traverses the tree and explores the node with the minimal aggregate distance iteratively. This method suffers from false hits arising from keyword tests. Thus, we propose the collaborative filtering technique, which performs keywords test by multiple keyword bitmaps collectively rather than by only one. Extensive experiments on both real and synthetic datasets demonstrate the superiority of our algorithms and optimizing strategies. Numéro de notice : A2018-364 Affiliation des auteurs : non IGN Thématique : GEOMATIQUE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10707-017-0315-0 Date de publication en ligne : 29/12/2017 En ligne : https://doi.org/10.1007/s10707-017-0315-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90726 [article]

The study of key issues about integration of GNSS and strong-motion records for real-time earthquake monitoring / Rui Tu in Advances in space research, vol 58 n° 3 (August 2016)  

Public [article]  inAdvances in space research > vol 58 n° 3 (August 2016) . - pp 304 - 309 Titre : The study of key issues about integration of GNSS and strong-motion records for real-time earthquake monitoring Type de document : Article/Communication Auteurs : Rui Tu, Auteur ; Pengfei Zhang, Auteur ; Rui Zhang, Auteur ; Jinhai Liu, Auteur Année de publication : 2016 Article en page(s) : pp 304 - 309 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] coordonnées GPS [Termes IGN] erreur systématique [Termes IGN] intégration de données [Termes IGN] qualité des données [Termes IGN] surveillance géologique [Termes IGN] temps réel Résumé : (auteur) This paper has studied the key issues about integration of GNSS and strong-motion records for real-time earthquake monitoring. The validations show that the consistence of the coordinate system must be considered firstly to exclude the system bias between GNSS and strong-motion. The GNSS sampling rate is suggested about 1–5 Hz, and we should give the strong-motion’s baseline shift with a larger dynamic noise as its variation is very swift. The initialization time of solving the baseline shift is less than one minute, and ambiguity resolution strategy is not greatly improved the solution. The data quality is very important for the solution, we advised to use multi-frequency and multi-system observations. These ideas give an important guide for real-time earthquake monitoring and early warning by the tight integration of GNSS and strong-motion records. Numéro de notice : A2016-589 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.asr.2016.04.033 En ligne : http://dx.doi.org/10.1016/j.asr.2016.04.033 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81744 [article]