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Raytracing atmospheric delays in ground-based GNSS reflectometry / T. Nicolaidou in Journal of geodesy, vol 94 n° 8 (August 2020)  

Public [article]  inJournal of geodesy > vol 94 n° 8 (August 2020) . - n° 68 Titre : Raytracing atmospheric delays in ground-based GNSS reflectometry Type de document : Article/Communication Auteurs : T. Nicolaidou, Auteur ; M.C. Santos, Auteur ; Simon D.P. Williams, Auteur ; et al., Auteur Année de publication : 2020 Article en page(s) : n° 68 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] coin réflecteur [Termes IGN] correction atmosphérique [Termes IGN] lancer de rayons [Termes IGN] modèle atmosphérique [Termes IGN] réflectométrie par GNSS [Termes IGN] réfraction [Termes IGN] temps de propagation Résumé : (auteur) Several studies have recognized that Global Navigation Satellite System Reflectometry (GNSS-R) is subject to atmospheric propagation delays. Unfortunately, there is little information in the peer-reviewed literature about the methods and algorithms involved in correcting for this effect. We have developed an atmospheric ray-tracing procedure to solve rigorously the three-point boundary value problem of ground-based GNSS-R observations. We defined the reflection-minus-direct or interferometric delay in terms of vacuum distance and radio length. We clarified the roles of linear and angular refraction in splitting the total delay in two components, along-path and geometric. We have introduced for the first time two subcomponents of the atmospheric geometric delay, the geometry shift and the geometric excess. We have defined corresponding atmospheric altimetry corrections necessary for unbiased altimetry retrievals. Using simulations, we examined the interferometric atmospheric delay for a range of typical scenarios, where it attained centimeter-level values at low satellite elevation angles ~ 5° for a 10-m high station. We found a linear and exponential dependence on reflector height and satellite elevation angle, respectively. A similar trend was found for the atmospheric altimetry correction, albeit with an amplified meter-level magnitude. The two delay components were similar near the horizon while the angular one vanished at zenith. For the altimetry correction components, both remained non-zero at zenith. We thus quantified the atmospheric bias in GNSS-R sea level retrievals. Numéro de notice : A2020-538 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-020-01390-8 Date de publication en ligne : 23/07/2020 En ligne : https://doi.org/10.1007/s00190-020-01390-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95731 [article]

Comparison of ray-tracing packages for troposphere delays / V. Nafisi in IEEE Transactions on geoscience and remote sensing, vol 50 n° 2 (February 2012)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 50 n° 2 (February 2012) . - pp 469 - 481 Titre : Comparison of ray-tracing packages for troposphere delays Type de document : Article/Communication Auteurs : V. Nafisi, Auteur ; L. Urquhart, Auteur ; M.C. Santos, Auteur ; et al., Auteur Année de publication : 2012 Article en page(s) : pp 469 - 481 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] erreur systématique [Termes IGN] lancer de rayons [Termes IGN] modèle atmosphérique [Termes IGN] propagation troposphérique [Termes IGN] réfraction atmosphérique Résumé : (Auteur) A comparison campaign to evaluate and compare troposphere delays from different ray-tracing software was carried out under the umbrella of the International Association of Geodesy Working Group 4.3.3 in the first half of 2010 with five institutions participating: the GFZ German Research Centre for Geosciences (GFZ), the Groupe de Recherche de Geodesie Spatiale, the National Institute of Information and Communications Technology (NICT), the University of New Brunswick, and the Institute of Geodesy and Geophysics of the Vienna University of Technology. High-resolution data from the operational analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) for stations Tsukuba (Japan) and Wettzell (Germany) were provided to the participants of the comparison campaign. The data consisted of geopotential differences with respect to mean sea level, temperature, and specific humidity, all at isobaric levels. Additionally, information about the geoid undulations was provided, and the participants computed the ray-traced total delays for 5° elevation angle and every degree in azimuth. In general, we find good agreement between the ray-traced slant factors from the different solutions at 5° elevation if determined from the same pressure level data of the ECMWF. Standard deviations and biases are at the 1-cm level (or significantly better for some combinations). Some of these discrepancies are due to differences in the algorithms and the interpolation approaches. If compared with slant factors determined from ECMWF native model level data, the biases can be significantly larger. Numéro de notice : A2012-045 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2011.2160952 Date de publication en ligne : 12/08/2011 En ligne : https://doi.org/10.1109/TGRS.2011.2160952 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31493 [article]

Exemplaires(1)

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065-2012021	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Brainy positioning: processing GPS data with neural networks / Rodrigo Figueiredo Leandro in GPS world, vol 18 n° 9 (September 2007)

Public [article]  inGPS world > vol 18 n° 9 (September 2007) . - pp 60 - 65 Titre : Brainy positioning: processing GPS data with neural networks Type de document : Article/Communication Auteurs : Rodrigo Figueiredo Leandro, Auteur ; C. Da Silva, Auteur ; P. Segantine, Auteur ; M.C. Santos, Auteur Année de publication : 2007 Article en page(s) : pp 60 - 65 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] phase GPS [Termes IGN] positionnement par GPS [Termes IGN] réseau neuronal artificiel [Termes IGN] simulation [Termes IGN] temps réel [Termes IGN] traitement de données GNSS Résumé : (Editeur) The brain is a fascinating organ. [...] In an effort to better understand how the brain works, neuroscientists teamed up with computer scientists to develop mathematical models to describe how networks of interconnected neurons process information. By the late 1950s, they had arrived at a basic model which has been improved on over the years. Each neuron in the network performs a simple computation; it receives signals from its input links, which it weights and then uses to compute its activation level (or output). The success of neural network models to mimic the basic operation of brain cells led computer scientists to the idea that artificial neural networks could be used to solve mathematical problems. They were able to show that, through a training or learning process, such networks are capable of solving virtually any problem that involves mapping input data to output data. Artificial neural networks have served as the basis for a variety of a tasks ranging from intelligent simulation, to real-time adaptation, to data analysis. While not a direct replacement for our traditional least-squares and Kalman filtering techniques, artificial neural networks have been used effectively for a number of applications in geodesy and navigation, including the processing of GPS data. But the handling of GPS data for use in a neural network processor is not without problems. In this month's column, we take a look at how artificial neural networks can be used as a tool in GPS applications, including the preprocessing necessary to successfully ingest the data. Copyright Questex Media Group Inc Numéro de notice : A2007-444 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28807 [article]

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067-07091	SL	Revue	Centre de documentation	Revues en salle	Disponible

Stochastic models for GPS positioning: an empirical approach / Rodrigo Figueiredo Leandro in GPS world, vol 18 n° 2 (February 2007)

Public [article]  inGPS world > vol 18 n° 2 (February 2007) . - pp 50 - 56 Titre : Stochastic models for GPS positioning: an empirical approach Type de document : Article/Communication Auteurs : Rodrigo Figueiredo Leandro, Auteur ; M.C. Santos, Auteur Année de publication : 2007 Article en page(s) : pp 50 - 56 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] antenne GPS [Termes IGN] matrice de covariance [Termes IGN] mesurage de pseudo-distance [Termes IGN] modèle stochastique [Termes IGN] perturbation [Termes IGN] positionnement par GPS [Termes IGN] qualité des données [Termes IGN] résidu Résumé : (Editeur) When processing GPS data, we should not only try to model the deterministic part of the measurements ; we should also try to account for their stochastic behavior, which is possible through use of the covariance matrix. Here, the authors present an empirical approach for building the covariance matrix of observations, with the ultimate goal to improve the quality of GPS data processing. Copyright Questex Media Group Inc Numéro de notice : A2007-070 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28435 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
067-07021	RAB	Revue	Centre de documentation	En réserve L003	Disponible