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The impact of second-order ionospheric delays on the ZWD estimation with GPS and BDS measurements / Shaocheng Zhang in GPS solutions, vol 24 n° 2 (April 2020)  

Public [article]  inGPS solutions > vol 24 n° 2 (April 2020) Titre : The impact of second-order ionospheric delays on the ZWD estimation with GPS and BDS measurements Type de document : Article/Communication Auteurs : Shaocheng Zhang, Auteur ; Lei Fang, Auteur ; Guangxing Wang, Auteur ; Wei Li, Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] champ géomagnétique [Termes descripteurs IGN] décalage d'horloge [Termes descripteurs IGN] données BeiDou [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] gradient d'ionosphère [Termes descripteurs IGN] méthode des moindres carrés [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] retard ionosphèrique [Termes descripteurs IGN] retard troposphérique zénithal [Termes descripteurs IGN] teneur verticale totale en électrons Résumé : (auteur) Since millimeter accuracy is required in many GNSS applications such as real-time zenith wet delay (ZWD) estimation, the higher-order ionospheric delays on GNSS signals are no longer negligible. We calculated the second-order ionospheric delays (I2) and analyzed the impact on the ZWD estimation with GPS-only and combined GPS/BDS observations. The undifferenced PPP model with fixed coordinates was used to estimate the ZWD and horizontal gradients. The method of blockwise sequential least squares was utilized to eliminate the receiver clock biases and compute the I2 impact on the ZWDs. The I2 delays on each GNSS satellite observations were calculated with the CODE final TEC map and the 12th generation of the international geomagnetic reference field (IGRF-12) model. The statistical results with the actual observation geometry show that the I2 delays can reach over 10 mm during the daytime, and the corresponding impact on the estimated ZWD can reach up to several millimeters. At station HKWS, the maximum I2 impact with GPS only reaches up to 3.1 mm and is still 2.4 mm when both GPS and BDS observations are used. The simulated I2 impact on the ZWD could reach several millimeters, even though the TEC and geomagnetic values were calculated from relatively moderate background models. Compared with the 5–10 mm precision of real-time ZWD estimation, the I2 delays must not be ignored, especially during high VTEC periods. Numéro de notice : A2020-082 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-020-0954-8 date de publication en ligne : 04/02/2020 En ligne : https://doi.org/10.1007/s10291-020-0954-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94651 [article]

Combinatorial optimization applied to VLBI scheduling / A. Corbin in Journal of geodesy, vol 94 n°2 (February 2020)  

Public [article]  inJournal of geodesy > vol 94 n°2 (February 2020) Titre : Combinatorial optimization applied to VLBI scheduling Type de document : Article/Communication Auteurs : A. Corbin, Auteur ; B. Niedermann, Auteur ; Axel Nothnagel, Auteur ; et al., Auteur Année de publication : 2020 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] analyse combinatoire (maths) [Termes descripteurs IGN] données VGOS [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] positionnement par ITGB [Termes descripteurs IGN] programmation linéaire [Termes descripteurs IGN] retard troposphérique zénithal [Termes descripteurs IGN] station VLBI [Termes descripteurs IGN] téléscope [Termes descripteurs IGN] temps universel coordonné Résumé : (auteur) Due to the advent of powerful solvers, today linear programming has seen many applications in production and routing. In this publication, we present mixed-integer linear programming as applied to scheduling geodetic very-long-baseline interferometry (VLBI) observations. The approach uses combinatorial optimization and formulates the scheduling task as a mixed-integer linear program. Within this new method, the schedule is considered as an entity containing all possible observations of an observing session at the same time, leading to a global optimum. In our example, the optimum is found by maximizing the sky coverage score. The sky coverage score is computed by a hierarchical partitioning of the local sky above each telescope into a number of cells. Each cell including at least one observation adds a certain gain to the score. The method is computationally expensive and this publication may be ahead of its time for large networks and large numbers of VLBI observations. However, considering that developments of solvers for combinatorial optimization are progressing rapidly and that computers increase in performance, the usefulness of this approach may come up again in some distant future. Nevertheless, readers may be prompted to look into these optimization methods already today seeing that they are available also in the geodetic literature. The validity of the concept and the applicability of the logic are demonstrated by evaluating test schedules for five 1-h, single-baseline Intensive VLBI sessions. Compared to schedules that were produced with the scheduling software sked, the number of observations per session is increased on average by three observations and the simulated precision of UT1-UTC is improved in four out of five cases (6 μs average improvement in quadrature). Moreover, a simplified and thus much faster version of the mixed-integer linear program has been developed for modern VLBI Global Observing System telescopes. Numéro de notice : A2020-153 Thématique : MATHEMATIQUE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01348-w date de publication en ligne : 29/01/2020 En ligne : https://doi.org/10.1007/s00190-020-01348-w Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94786 [article]

Assessment of the positioning performance and tropospheric delay retrieval with precise point positioning using products from different analysis centers / Feng Zhou in GPS solutions, vol 24 n° 1 (January 2020)  

Public [article]  inGPS solutions > vol 24 n° 1 (January 2020) Titre : Assessment of the positioning performance and tropospheric delay retrieval with precise point positioning using products from different analysis centers Type de document : Article/Communication Auteurs : Feng Zhou, Auteur ; Xinyun Cao, Auteur ; Yulong Ge, Auteur ; Weiwei Li, Auteur Année de publication : 2020 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes descripteurs IGN] distance zénithale [Termes descripteurs IGN] positionnement par GNSS [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] précision du positionnement [Termes descripteurs IGN] propagation troposphérique [Termes descripteurs IGN] retard troposphérique [Termes descripteurs IGN] temps de convergence Résumé : (Auteur) The performance of precise point positioning (PPP) strongly depends on the quality of satellite orbit and clock products. To give a full evaluation of PPP performance with the various publicly available precise satellite orbit and clock products, this contribution comprehensively investigates the positioning performance as well as tropospheric delay retrieval of GPS-, GLONASS-, and Galileo-only PPP with the precise products from eight International GNSS Service (IGS) (i.e., cod, emr, esa, gfz, grg, igs, jpl, and mit) and five multi-GNSS experiment (MGEX) analysis centers (ACs) (i.e., com, gbm, grm, jax, and wum) based on the observations of 90 MGEX tracking stations in a 1-month period (April 2019). The positioning performance in terms of convergence time and positioning accuracy is assessed by coordinate-static and coordinate-kinematic PPP modes, while the tropospheric delay estimation in terms of accuracy is evaluated by coordinate-fixed PPP mode. For GPS- and GLONASS-only PPP with different AC products, the positioning performances are comparable with each other except that with emr, jpl, mit, and jax products. Overall, the positioning performance with cod and com products provided by CODE ranks the first. For Galileo-only PPP, the grm product performs the best. For ZTD estimation, the accuracy derived from GPS-, GLONASS-, and Galileo-only solutions agrees well and the differences in accuracy among different AC products can be negligible. Numéro de notice : A2020-022 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-019-0925-0 date de publication en ligne : 19/11/2019 En ligne : https://doi.org/10.1007/s10291-019-0925-0 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94463 [article]

Estimation and representation of regional atmospheric corrections for augmenting real-time single-frequency PPP / Peiyuan Zhou in GPS solutions, vol 24 n° 1 (January 2020)  

Public [article]  inGPS solutions > vol 24 n° 1 (January 2020) Titre : Estimation and representation of regional atmospheric corrections for augmenting real-time single-frequency PPP Type de document : Article/Communication Auteurs : Peiyuan Zhou, Auteur ; Jin Wang, Auteur ; Zhixi Nie, Auteur ; Yang Gao, Auteur Année de publication : 2020 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes descripteurs IGN] correction atmosphérique [Termes descripteurs IGN] correction ionosphérique [Termes descripteurs IGN] correction troposphérique [Termes descripteurs IGN] décalage d'horloge [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] Quasi-Zenith Satellite System [Termes descripteurs IGN] récepteur monofréquence [Termes descripteurs IGN] retard ionosphèrique [Termes descripteurs IGN] retard troposphérique [Termes descripteurs IGN] satellite GPS [Termes descripteurs IGN] station GNSS [Termes descripteurs IGN] temps réel [Termes descripteurs IGN] teneur totale en électrons Résumé : (Auteur) Real-time single-frequency precise point positioning (PPP) can be significantly augmented by applying high-quality atmospheric corrections. In previous work, the satellite-and-station-specific slant total electron content (STEC) ionospheric corrections, derived from a regional reference network, are commonly used to augment single-frequency PPP for improving positioning accuracy and faster convergence. However, since the users are required to interpolate STEC ionospheric corrections from nearby reference stations, either duplex communication links should be established or all corrections of the reference network must be retrieved, which makes it inefficient to provide augmentation services to many users. Moreover, the regional tropospheric corrections are generally neglected in augmenting real-time single-frequency PPP. In this study, we present a method to estimate and represent tropospheric and ionospheric corrections from a regional reference network, which can be efficiently disseminated to users through a simplex communication link. First, the uncombined dual-frequency PPP, with external ionospheric constraints derived from international GNSS service predicted global ionospheric map, is used for estimating atmospheric delays with observations from a regional GNSS reference network. Then, the atmospheric delays are properly represented to facilitate real-time transmission by applying a polynomial model for the representation of zenith wet tropospheric corrections, and satellite-specific STEC maps for representing the slant ionospheric corrections. The above results in only simple communication links required to retrieve the regional atmospheric corrections for real-time single-frequency PPP augmentation. Observations from a regional network of 30 GNSS reference stations with inter-station distances of about 70 km during a 1-week-long period, including both quiet and active geomagnetic conditions, are used for generating the regional atmospheric corrections. The results indicate that the average root-mean-square errors of the obtained regional tropospheric and ionospheric corrections are better than 0.01 and 0.05 m when compared with those derived from dual-frequency uncombined PPP, respectively. The positioning accuracy of the single-frequency PPP augmented with regional atmospheric corrections is at 0.141 m horizontally and 0.206 m vertically under a 95% confidence level, a significant improvement compared to single-frequency PPP without atmospheric augmentation. The convergence time is also significantly reduced with 70.4% of the positioning sessions achieving instantaneous 3D convergence. Numéro de notice : A2020-023 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-019-0920-5 date de publication en ligne : 13/11/2019 En ligne : https://doi.org/10.1007/s10291-019-0920-5 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94466 [article]

Troposphere delay modeling with horizontal gradients for satellite laser ranging / M. Drożdżewski in Journal of geodesy, vol 93 n°10 (October 2019)  

Public [article]  inJournal of geodesy > vol 93 n°10 (October 2019) Titre : Troposphere delay modeling with horizontal gradients for satellite laser ranging Type de document : Article/Communication Auteurs : M. Drożdżewski, Auteur ; Krzysztof Sosnica, Auteur ; Florian Zus, Auteur ; Kyriakos Balidakis, Auteur Année de publication : 2019 Note générale : bibbliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] angle vertical [Termes descripteurs IGN] coordonnées polaires [Termes descripteurs IGN] dissymétrie [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] géocentre [Termes descripteurs IGN] gradient de troposphère [Termes descripteurs IGN] interférométrie à très grande base [Termes descripteurs IGN] Lageos [Termes descripteurs IGN] retard troposphérique [Termes descripteurs IGN] Sentinel-3 [Termes descripteurs IGN] station TLS (télémétrie) [Termes descripteurs IGN] télémètre laser sur satellite Résumé : (auteur) Satellite laser ranging (SLR) constitutes a fundamental space geodetic technique providing global geodetic parameters, such as geocenter coordinates, Earth rotation parameters, and low-degree gravity field coefficients. The tropospheric delay correction is one of the crucial corrections that have to be taken into account when processing SLR data. Current conventional models of the troposphere delays assume a full symmetry of the atmosphere above SLR stations. Neglecting horizontal gradients in SLR solutions introduces a systematic error in SLR products, especially for the observations at low elevation angles, and leads to a deterioration of the consistency between SLR and other space geodetic techniques, such as global navigational satellite systems and very-long-baseline interferometry. We derive new mapping function coefficients, as well as first- and second-order horizontal gradients, all of which are based on numerical weather models, in order to properly consider the azimuthal asymmetry in SLR solutions. We test the enhanced mapping function and horizontal gradients on the solutions based on 11 years of SLR observations to LAGEOS-1/2 satellites and 1 year of SLR observations to Sentinel-3A. The consideration of azimuthal asymmetry of the atmosphere above the SLR stations has a systematic effect on SLR-derived products, such as station and geocenter coordinates and pole coordinates. Horizontal gradients in SLR solutions improve the consistency between SLR-derived pole coordinates and the combined IERS-C04 series by means of reducing the offset for the X and Y pole coordinates by 20 μas. The second-order horizontal gradients are negligible in SLR solutions; thus, including first-order gradients is sufficient for SLR solutions. Numéro de notice : A2019-607 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-019-01287-1 date de publication en ligne : 22/08/2019 En ligne : https://doi.org/10.1007/s00190-019-01287-1 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94790 [article]

Modeling the VLBI delay for Earth satellites / Frédéric Jaron in Journal of geodesy, vol 93 n°7 (July 2019)  

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Parallel computation of regional CORS network corrections based on ionospheric-free PPP / Linyang Li in GPS solutions, vol 23 n° 3 (July 2019)  

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Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa / Samuel Nahmani in Atmospheric chemistry and physics, vol 19 n° 14 (juillet 2019)    

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High-resolution models of tropospheric delays and refractivity based on GNSS and numerical weather prediction data for alpine regions in Switzerland / Karina Wilgan in Journal of geodesy, vol 93 n°6 (June 2019)  

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The impact of relative and absolute GNSS positioning strategies on estimated coordinates and ZWD in the framework of meteorological applications / Alessandro Fermi in Applied geomatics, vol 11 n° 1 (March 2019)  

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A new global grid model for the determination of atmospheric weighted mean temperature in GPS precipitable water vapor / Liangke Huang in Journal of geodesy, vol 93 n° 2 (February 2019)  

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Impact of GPS antenna phase center models on zenith wet delay and tropospheric gradients / Yohannes Getachew Ejigu in GPS solutions, vol 23 n° 1 (January 2019)  

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Atmospheric artifacts correction with a covariance-weighted linear model over mountainous regions / Zhongbo Hu in IEEE Transactions on geoscience and remote sensing, vol 56 n° 12 (December 2018)  

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Performance analysis of PPP positioning method by using IGS real-time service / Tatjana Kuzmić in Geodetski vestnik, vol 62 n° 4 (December 2018 - February 2019)  

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PPPH : a MATLAB-based software for multi-GNSS precise point positioning analysis / Berkay Bahadur in GPS solutions, vol 22 n° 4 (October 2018)  

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