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The construction of sound speed field based on back propagation neural network in the global ocean / Junting Wang in Marine geodesy, vol 43 n° 6 (November 2020)  

Public [article]  inMarine geodesy > vol 43 n° 6 (November 2020) . - pp 621 - 642 Titre : The construction of sound speed field based on back propagation neural network in the global ocean Type de document : Article/Communication Auteurs : Junting Wang, Auteur ; Tianhe Xu, Auteur ; Wenfeng Nie, Auteur ; et al., Auteur Année de publication : 2020 Article en page(s) : pp 621 - 642 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] fonction orthogonale [Termes IGN] interpolation spatiale [Termes IGN] milieu marin [Termes IGN] onde acoustique [Termes IGN] propagation du son [Termes IGN] réseau neuronal artificiel [Termes IGN] salinité [Termes IGN] sondage acoustique [Termes IGN] température [Termes IGN] vitesse Résumé : (auteur) The sound speed is a key parameter that affects the underwater acoustic positioning and navigation. Aiming at the high-precision construction of sound speed field in the complex marine environment, this paper proposes a sound speed field model based on back propagation neural network (BPNN) by considering the correlation of learning samples. The method firstly uses measured ocean parameters to construct the temperature and salinity field. Then the spatial position, the temperature and the salinity information are used to construct the global ocean sound speed field based on the back propagation neural network algorithm. During the processing, the learning samples of back propagation neural network are selected based on the correlation between sound speed and distance. The proposed algorithm is validated by the global Argo data as well as compared with the spatial interpolation and the empirical orthogonal function (EOF) algorithm. The results demonstrate that the average root mean squares of the BPNN considering the correlation of learning samples is 0.352 m/s compared to the 1.527 m/s of EOF construction and the 2.661 m/s of spatial interpolation, with an improvement of 76.9% and 86.8%. Therefore, the proposed algorithm can improve the construction accuracy of sound speed field in the complex marine environment. Numéro de notice : A2020-694 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01490419.2020.1815912 date de publication en ligne : 14/09/2020 En ligne : https://doi.org/10.1080/01490419.2020.1815912 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96242 [article]

Improved arctic ocean mass variability inferred from time-variable gravity with constraints and dual leakage correction / Dapeng Mu in Marine geodesy, Vol 43 n° 3 (May 2020)  

Public [article]  inMarine geodesy > Vol 43 n° 3 (May 2020) . - pp 269 - 284 Titre : Improved arctic ocean mass variability inferred from time-variable gravity with constraints and dual leakage correction Type de document : Article/Communication Auteurs : Dapeng Mu, Auteur ; Tianhe Xu, Auteur ; Guochang Xu, Auteur Année de publication : 2020 Article en page(s) : pp 269 - 284 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] Arctique, océan [Termes IGN] données GRACE [Termes IGN] harmonique sphérique [Termes IGN] marée océanique Résumé : (Auteur) The ocean mass variability inferred from Gravity Recovery and Climate Experiment (GRACE) satellites mission is challenged by the stripes and the leakage across land-ocean boundary. The recently released GRACE mascons solutions are advanced by applying constraints that remove efficiently the stripes and dual leakage correction that restores the coastal ocean mass variability. Here we quantitatively evaluate the improvement in the Arctic Ocean mass variability by GRACE mascons. To do so, we compare the combination of GRACE solutions (including the mascons solutions and traditional spherical harmonic coefficients (SHCs) solutions) and the steric estimates against the altimeter observations. Our results suggest that mascons solutions produce stronger correlations compared to SHCs solutions, especially along the coastal zone, indicating the importance of the dual leakage correction. Stronger correlation is produced by the mascons over a small basin in the interior of the Arctic Ocean, suggesting that mascons solutions deliver better ocean mass variability than the SHCs solutions. Since the comparisons are carried out over two sub-basins, we conclude that mascons are able to provide better regional ocean mass variability that may have implications for regional sea level budget, in particular over the coastal zone. Numéro de notice : A2020-185 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01490419.2020.1711832 date de publication en ligne : 17/01/2020 En ligne : https://doi.org/10.1080/01490419.2020.1711832 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94975 [article]

Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS / Wenfeng Nie in GPS solutions, vol 22 n° 3 (July 2018)  

Public [article]  inGPS solutions > vol 22 n° 3 (July 2018) Titre : Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS Type de document : Article/Communication Auteurs : Wenfeng Nie, Auteur ; Tianhe Xu, Auteur ; Adria Rovira-Garcia, Auteur ; José Miguel Juan Zornoza, Auteur ; Jaume Sanz, Auteur ; Guillermo Gonzalez-Casado, Auteur ; Chen Wu, Auteur ; Guochang Xu, Auteur Année de publication : 2018 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] code GPS [Termes IGN] coordonnées GPS [Termes IGN] erreur systématique [Termes IGN] étalonnage des données [Termes IGN] station permanente [Termes IGN] teneur totale en électrons Mots-clés libres : differential code bias Résumé : (Auteur) The calibration errors on experimental slant total electron content (TEC) determined with global positioning system (GPS) observations is revisited. Instead of the analysis of the calibration errors on the carrier phase leveled to code ionospheric observable, we focus on the accuracy analysis of the undifferenced ambiguity-fixed carrier phase ionospheric observable determined from a global distribution of permanent receivers. The results achieved are: (1) using data from an entire month within the last solar cycle maximum, the undifferenced ambiguity-fixed carrier phase ionospheric observable is found to be over one order of magnitude more accurate than the carrier phase leveled to code ionospheric observable and the raw code ionospheric observable. The observation error of the undifferenced ambiguity-fixed carrier phase ionospheric observable ranges from 0.05 to 0.11 total electron content unit (TECU) while that of the carrier phase leveled to code and the raw code ionospheric observable is from 0.65 to 1.65 and 3.14 to 7.48 TECU, respectively. (2) The time-varying receiver differential code bias (DCB), which presents clear day boundary discontinuity and intra-day variability pattern, contributes the most part of the observation error. This contribution is assessed by the short-term stability of the between-receiver DCB, which ranges from 0.06 to 0.17 TECU in a single day. (3) The remaining part of the observation errors presents a sidereal time cycle pattern, indicating the effects of the multipath. Further, the magnitude of the remaining part implies that the code multipath effects are much reduced. (4) The intra-day variation of the between-receiver DCB of the collocated stations suggests that estimating DCBs as a daily constant can have a mis-modeling error of at least several tenths of 1 TECU. Numéro de notice : A2018-372 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-018-0753-7 date de publication en ligne : 26/06/2018 En ligne : https://doi.org/10.1007/s10291-018-0753-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90766 [article]

GPS/BDS short-term ISB modelling and prediction / Nan Jiang in GPS solutions, vol 21 n° 1 (January 2017)  

Public [article]  inGPS solutions > vol 21 n° 1 (January 2017) . - pp 163 - 175 Titre : GPS/BDS short-term ISB modelling and prediction Type de document : Article/Communication Auteurs : Nan Jiang, Auteur ; Yan Xu, Auteur ; Tianhe Xu, Auteur ; et al., Auteur Année de publication : 2017 Article en page(s) : pp 163 - 175 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] analyse comparative [Termes IGN] données BeiDou [Termes IGN] données GNSS [Termes IGN] erreur systématique [Termes IGN] erreur systématique inter-systèmes [Termes IGN] méthode des moindres carrés [Termes IGN] modèle d'erreur [Termes IGN] orbitographie [Termes IGN] positionnement par BeiDou [Termes IGN] positionnement par GNSS [Termes IGN] positionnement ponctuel précis Résumé : (Auteur) The Chinese BeiDou Navigation Satellite System (BDS) has completed its first milestone by providing coverage of the Asia–Pacific area navigation service since December 27, 2012. With the combination of BDS, the GNSS precise point positioning (PPP) can improve its positioning accuracy, availability and reliability. However, in order to achieve the best positioning solutions, the inter-system bias (ISB) between GPS and BDS must be resolved as precisely as possible. In this study, a 1-week period (GPS week 1810) of GPS/BDS observations for 18 distributed stations from the International GNSS Service Multi-GNSS Experiment are processed. Primarily, the ISB is estimated by an extended Kalman filter as a piece-wise parameter every 30 min. Then we generate a smoothed ISB series (ISB_s) with a sliding window median filter to reject the outliers from the original estimated ISB series (ISB_o). After analysing the characteristics of the ISB_s, a short-term station-dependent ISB model based on a 1-week period is proposed in this study. This model consists of a quadratic polynomial in time and two or three periodic functions with diurnal and semi-diurnal periods. Frequency spectrum analysis is used to determine the periods of the periodic functions, and the coefficients of the quadratic function and the periodic functions are estimated by least squares. For model verification, we compare the ISB derived from the model (ISB_m) with ISB_s (assumed the true values). The comparisons indicate an almost normal distribution. It is found that the proposed model is consistent with the true values: the root-mean-square (RMS) values being about 0.7 ns, and some stations are even better. This means that the short-term ISB model proposed has a high fitting accuracy. Hence, it can be used for ISB prediction. Comparing the prediction ISB series (ISB_p) with ISB_s in the following week (GPS week 1811), we can draw the conclusion that the accuracy of the prediction declines with an increase in the time period. The 1-day period precision can achieve 0.57–1.21 ns, while the accuracy of the 2-day prediction decreases to 0.77–1.72 ns. Hence, we recommend a predicting duration of 1 day. The proposed model will be beneficial for subsequent GPS/BDS PPP or precise orbit determination (POD) since the ISB derived from this model can be considered as a priori constraint in the PPP/POD solutions. With this a priori constraint, the convergence time can be shortened by 19.6, 16.1 and 2.4 % in N, E and U components, respectively. The accuracy of result in the E component is remarkably improved by 11.9 %. Numéro de notice : A2017-015 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0513-x date de publication en ligne : 09/01/2016 En ligne : https://doi.org/10.1007/s10291-015-0513-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83946 [article]

GNSS navigation and positioning for the GEOHALO experiment in Italy / Kaifei He in GPS solutions, vol 20 n° 2 (April 2016)  

Public [article]  inGPS solutions > vol 20 n° 2 (April 2016) . - pp 215 - 224 Titre : GNSS navigation and positioning for the GEOHALO experiment in Italy Type de document : Article/Communication Auteurs : Kaifei He, Auteur ; Guochang Xu, Auteur ; Tianhe Xu, Auteur ; Frank Flechtner, Auteur Année de publication : 2016 Article en page(s) : pp 215 - 224 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] données HALO [Termes IGN] gravimétrie aérienne [Termes IGN] Italie [Termes IGN] positionnement cinématique [Termes IGN] positionnement par GNSS Résumé : (Auteur) GEOHALO is a joint experiment of several German institutes for atmospheric research and earth observation where exploring airborne gravimetry over Italy using the High Altitude and LOng Range (HALO) aircraft data is one of the major goals. The kinematic positioning of the aircraft, on which all remote sensing instruments are located, by Global Navigation Satellite System (GNSS) is affected by the characteristics of long-distance, long-time duration, and high-platform dynamics which are a key factor for the success of the GEOHALO project. We outline the strategy and method of GNSS data processing which takes into account multiple GNSS systems (GPS and GLONASS), multiple static reference stations including stations from the International GNSS Service (IGS) and the EUropean REFerence network (EUREF), multiple GNSS-receiving equipments mounted on the kinematic platform, geometric relations between multiple antennas, and assumptions of similar characteristic of atmospheric effects within a small area above the aircraft. From this precondition, various data processing methods for kinematic positioning have been developed, applied and compared. It is shown that the proposed method based on multiple reference stations and multiple kinematic stations with a common atmospheric delay parameter can effectively improve the reliability and accuracy of GNSS kinematic positioning. Numéro de notice : A2016-612 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1007/s10291-014-0430-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81811 [article]