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An advanced GNSS code multipath detection and estimation algorithm / Negin Sokhandan in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 627 - 640 Titre : An advanced GNSS code multipath detection and estimation algorithm Type de document : Article/Communication Auteurs : Negin Sokhandan, Auteur ; James T. Curran, Auteur ; Ali Broumandan, Auteur ; Gérard Lachapelle, Auteur Année de publication : 2016 Article en page(s) : pp 627 - 640 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] code GNSS [Termes IGN] méthode du maximum de vraisemblance (estimation) [Termes IGN] milieu urbain [Termes IGN] modèle de simulation [Termes IGN] positionnement par GNSS [Termes IGN] système de navigation [Termes IGN] trajet multiple Résumé : (Auteur) A novel maximum likelihood-based range estimation algorithm is designed to provide robustness to multipath, which is recognized as a dominant error source in DS-CDMA-based navigation systems. The detection–estimation problem is jointly solved to sequentially estimate the parameters of each individual multipath component and predict the existence of a next possible component. A comparison between contemporary maximum likelihood-based multipath estimation techniques and this new technique is provided. A selection of realistic channel simulation models is used to assess relative performance under different operating situations. A set of real GPS L1/CA data processing results are also presented to further assess the applicability of the proposed algorithm for urban navigation. Numéro de notice : A2016--025 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0475-z En ligne : http://dx.doi.org/10.1007/s10291-015-0475-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83926 [article]

Long-term soil moisture dynamics derived from GNSS interferometric reflectometry: a case study for Sutherland, South Africa / Sibylle Vey in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 641 - 654 Titre : Long-term soil moisture dynamics derived from GNSS interferometric reflectometry: a case study for Sutherland, South Africa Type de document : Article/Communication Auteurs : Sibylle Vey, Auteur ; Jens Wickert, Auteur Année de publication : 2016 Article en page(s) : pp 641 - 654 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Afrique du sud (état) [Termes IGN] analyse diachronique [Termes IGN] humidité du sol [Termes IGN] rapport signal sur bruit [Termes IGN] récepteur GNSS [Termes IGN] réflectométrie par GNSS [Termes IGN] signal GNSS [Termes IGN] variation temporelle Résumé : (Auteur) Soil moisture is a geophysical key observable for predicting floods and droughts, modeling weather and climate and optimizing agricultural management. Currently available in situ observations are limited to small sampling volumes and restricted number of sites, whereas measurements from satellites lack spatial resolution. Global navigation satellite system (GNSS) receivers can be used to estimate soil moisture time series at an intermediate scale of about 1000 m2. In this study, GNSS signal-to-noise ratio (SNR) data at the station Sutherland, South Africa, are used to estimate soil moisture variations during 2008–2014. The results capture the wetting and drying cycles in response to rainfall. The GNSS Volumetric Water Content (VWC) is highly correlated (r2 = 0.8) with in situ observations by time-domain reflectometry sensors and is accurate to 0.05 m3/m3. The soil moisture estimates derived from the SNR of the L1 and L2P signals compared to the L2C show small differences with a RMSE of 0.03 m3/m3. A reduction in the SNR sampling rate from 1 to 30 s has very little impact on the accuracy of the soil moisture estimates (RMSE of the VWC difference 1–30 s is 0.01 m3/m3). The results show that the existing data of the global tracking network with continuous observations of the L1 and L2P signals with a 30-s sampling rate over the last two decades can provide valuable complementary soil moisture observations worldwide. Numéro de notice : A2016--026 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0474-0 En ligne : http://dx.doi.org/10.1007/s10291-015-0474-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83927 [article]

On the significance of periodic signals in noise analysis of GPS station coordinates time series / Janusz Bogusz in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 655 - 664 Titre : On the significance of periodic signals in noise analysis of GPS station coordinates time series Type de document : Article/Communication Auteurs : Janusz Bogusz, Auteur ; Anna Klos, Auteur Année de publication : 2016 Article en page(s) : pp 655 - 664 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] analyse diachronique [Termes IGN] bruit (théorie du signal) [Termes IGN] coordonnées cartésiennes géocentriques [Termes IGN] GIPSY-OASIS [Termes IGN] positionnement ponctuel précis [Termes IGN] série temporelle [Termes IGN] signal GPS [Termes IGN] station GPS [Termes IGN] variation saisonnière [Termes IGN] vitesse Résumé : (Auteur) Each of the GPS-derived time series consists of the deterministic (functional) and stochastic part. We propose that the deterministic part includes all periodicities from 1st to 9th harmonics of residual Chandler, tropical and draconitic periods and compare it with commonly used calculations of the annual and semi-annual tropical curve. Then, we address the issues of whether all residual periodicities, as proposed here, need to be taken into consideration when performing noise analysis. We use the position time series from 180 International GNSS Service stations obtained at the Jet Propulsion Laboratory using the GIPSY-OASIS software in a Precise Point Positioning mode. The longest series has 22.1 years of GPS daily solutions. The spectral indices range from –0.12 to –0.92, while the median values of “global” spectral indices are equal to: –0.41 ± 0.15, –0.38 ± 0.12 and –0.33 ± 0.18 for North, East and Up components, respectively. All non-modelled geophysical processes or non-included artificial effects in time series lead to an underestimation of errors of velocities, but also to changes in the velocity values themselves. The proposed assumption of seasonals subtraction caused the Akaike information criterion values to show a decrease in the median value of 30 %, which in fact means that all the seasonals mentioned here must be taken into account when analyzing noises. Finally, we noticed that there are some of the GPS stations that improved their velocity uncertainty even of 56 %. Numéro de notice : A2016--027 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0478-9 En ligne : http://dx.doi.org/10.1007/s10291-015-0478-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83929 [article]

Using a regional numerical weather prediction model for GNSS positioning over Brazil / Daniele Barroca Marra Alves in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 677 - 685 Titre : Using a regional numerical weather prediction model for GNSS positioning over Brazil Type de document : Article/Communication Auteurs : Daniele Barroca Marra Alves, Auteur ; Luiz Fernando Sapucci, Auteur ; Haroldo Antonio Marques, Auteur ; et al., Auteur Année de publication : 2016 Article en page(s) : pp 677 - 685 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Amazonie [Termes IGN] Brésil [Termes IGN] modèle de simulation [Termes IGN] modèle météorologique [Termes IGN] positionnement ponctuel précis [Termes IGN] propagation troposphérique [Termes IGN] station GNSS [Termes IGN] teneur en vapeur d'eau [Termes IGN] troposphère Résumé : (Auteur) The global navigation satellite system (GNSS) can provide centimeter positioning accuracy at low costs. However, in order to obtain the desired high accuracy, it is necessary to use high-quality atmospheric models. We focus on the troposphere, which is an important topic of research in Brazil where the tropospheric characteristics are unique, both spatially and temporally. There are dry regions, which lie mainly in the central part of the country. However, the most interesting area for the investigation of tropospheric models is the wet region which is located in the Amazon forest. This region substantially affects the variability of humidity over other regions of Brazil. It provides a large quantity of water vapor through the humidity convergence zone, especially for the southeast region. The interconnection and large fluxes of water vapor can generate serious deficiencies in tropospheric modeling. The CPTEC/INPE (Center for Weather Forecasting and Climate Studies/Brazilian Institute for Space Research) has been providing since July 2012 a numerical weather prediction (NWP) model for South America, known as Eta. It has yield excellent results in weather prediction but has not been used in GNSS positioning. This NWP model was evaluated in precise point positioning (PPP) and network-based positioning. Concerning PPP, the best positioning results were obtained for the station SAGA, located in Amazon region. Using the NWP model, the 3D RMS are less than 10 cm for all 24 h of data, whereas the values reach approximately 60 cm for the Hopfield model. For network-based positioning, the best results were obtained mainly when the tropospheric characteristics are critical, in which case an improvement of up to 7.2 % was obtained in 3D RMS using NWP models. Numéro de notice : A2016--028 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0477-x En ligne : http://dx.doi.org/10.1007/s10291-015-0477-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83930 [article]

Generating GPS satellite fractional cycle bias for ambiguity-fixed precise point positioning / Pan Li in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 771 - 782 Titre : Generating GPS satellite fractional cycle bias for ambiguity-fixed precise point positioning Type de document : Article/Communication Auteurs : Pan Li, Auteur ; Xiaohong Zhang, Auteur ; Xiaodong Ren, Auteur ; et al., Auteur Année de publication : 2016 Article en page(s) : pp 771 - 782 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] données GRACE [Termes IGN] erreur systématique [Termes IGN] positionnement ponctuel précis [Termes IGN] résolution d'ambiguïté Résumé : (Auteur) With the development of precise point positioning (PPP), the School of Geodesy and Geomatics (SGG) at Wuhan University is now routinely producing GPS satellite fractional cycle bias (FCB) products with open access for worldwide PPP users to conduct ambiguity-fixed PPP solution. We provide a brief theoretical background of PPP and present the strategies and models to compute the FCB products. The practical realization of the two-step (wide-lane and narrow-lane) FCB estimation scheme is described in detail. With GPS measurements taken in various situations, i.e., static, dynamic, and on low earth orbit (LEO) satellites, the quality of FCB estimation and the effectiveness of PPP ambiguity resolution (AR) are evaluated. The comparison with CNES FCBs indicated that our FCBs had a good consistency with the CNES ones. For wide-lane FCB, almost all the differences of the two products were within ±0.05 cycles. For narrow-lane FCB, 87.8 % of the differences were located between ±0.05 cycles, and 97.4 % of them were located between ±0.075 cycles. The experimental results showed that, compared with conventional ambiguity-float PPP, the averaged position RMS of static PPP can be improved from (3.6, 1.4, 3.6) to (2.0, 1.0, 2.7) centimeters for ambiguity-fixed PPP. The average accuracy improvement in the east, north, and up components reached 44.4, 28.6, and 25.0 %, respectively. A kinematic, ambiguity-fixed PPP test with observation of 80 min achieved a position accuracy of better than 5 cm at the one-sigma level in all three coordinate components. Compared with the results of ambiguity-float, kinematic PPP, the positioning biases of ambiguity-fixed PPP were improved by about 78.2, 20.8, and 65.1 % in east, north, and up. The RMS of LEO PPP test was improved by about 23.0, 37.0, and 43.0 % for GRACE-A and GRACE-B in radial, tangential, and normal directions when AR was applied to the same data set. These results demonstrated that the SGG FCB products can be produced with high quality for users anywhere around the world to carry out ambiguity-fixed PPP solutions. Numéro de notice : A2016--029 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0483-z En ligne : http://dx.doi.org/10.1007/s10291-015-0483-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83931 [article]

Ionospheric tomography using GNSS: multiplicative algebraic reconstruction technique applied to the area of Brazil / Fabricio Dos Santos Prol in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 807 - 814 Titre : Ionospheric tomography using GNSS: multiplicative algebraic reconstruction technique applied to the area of Brazil Type de document : Article/Communication Auteurs : Fabricio Dos Santos Prol, Auteur ; Paulo de Oliveira Camargo, Auteur Année de publication : 2016 Article en page(s) : pp 807 - 814 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Brésil [Termes IGN] code GNSS [Termes IGN] International Reference Ionosphere [Termes IGN] modèle ionosphérique [Termes IGN] phase GNSS [Termes IGN] récepteur GNSS [Termes IGN] teneur totale en électrons [Termes IGN] tomographie par GPS Résumé : (Auteur) Experimental analysis was performed using multiplicative algebraic reconstruction technique (MART) to map the ionosphere over Brazil. Code and phase observations from the global navigation satellite system (GNSS) together with the international reference ionosphere (IRI) enabled the estimation of ionospheric profiles and total electron content (TEC) over the entire region. Twenty-four days of data collected from existing ground-based GNSS receivers during the recent solar maximum period were used to analyze the performance of the MART algorithm. The results were compared with four ionosondes. It was demonstrated that MART estimated the electron density peak with the same degree of accuracy as the IRI model in regions with appropriate geometrical coverage by GNSS receivers for tomographic reconstruction. In addition, the slant TEC, as estimated with MART, presented lower root-mean-square error than the TEC calculated by ionospheric maps available from the International GNSS Service (IGS). Furthermore, the daily variations of the ionosphere were better represented with the algebraic techniques, compared to the IRI model and IGS maps, enabling a correlation of the elevation of the ionosphere at higher altitudes with the equatorial ionization anomaly intensification. The tomographic representations also enabled the detection of high vertical gradients at the same instants in which ionospheric irregularities were evident. Numéro de notice : A2016--030 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0490-0 En ligne : http://dx.doi.org/10.1007/s10291-015-0490-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83932 [article]