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Auteur Simon D.P. Williams |
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Affiner la recherche Interroger des sources externesRaytracing atmospheric delays in ground-based GNSS reflectometry / T. Nicolaidou in Journal of geodesy, vol 94 n° 8 (August 2020)
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 propagationRésumé : (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
in Journal of geodesy > vol 94 n° 8 (August 2020) . - n° 68[article]
Titre : Improved constraints on models of glacial isostatic adjustment: A review of the contribution of ground-based geodetic observations Type de document : Article/Communication Auteurs : Matt A. King, Auteur ; Zuheir Altamimi Année de publication : 2010 Article en page(s) : pp 465 - 507 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Antarctique
[Termes IGN] bilan de masse
[Termes IGN] calotte glaciaire
[Termes IGN] champ de vitesse
[Termes IGN] données GRACE
[Termes IGN] Groenland
[Termes IGN] mesure géodésique
[Termes IGN] positionnement par DORIS
[Termes IGN] positionnement par GPS
[Termes IGN] positionnement par ITGB
[Termes IGN] positionnement par télémétrie laser sur satellite
[Termes IGN] rebond post-glaciaireRésumé : (auteur) The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth’s interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates. Numéro de notice : A2010-663 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10712-010-9100-4 Date de publication en ligne : 16/06/2010 En ligne : https://doi.org/10.1007/s10712-010-9100-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91769
in Surveys in Geophysics > vol 31 n° 5 (September 2010) . - pp 465 - 507[article]Documents numériques
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Titre : Characterizing long‐time scale hydrological effects on gravity for improved distinction of tectonic signals Type de document : Article/Communication Auteurs : Michel Van Camp, Auteur ; Laurent Métivier Année de publication : 2010 Article en page(s) : 10 p. Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] pesanteur terrestre
[Termes IGN] surcharge hydrologique
[Termes IGN] tectoniqueNuméro de notice : A2010-646 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2009JB006615 Date de publication en ligne : 16/07/2010 En ligne : https://doi.org/10.1029/2009JB006615 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90746
in Journal of geophysical research : Solid Earth > Vol 115 n° B7 (July 2010) . - 10 p.[article]Documents numériques
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Characterizing long‐time scale hydrological effects ... - pdf éditeurAdobe Acrobat PDF
Titre : Rates of sea‐level change over the past century in a geocentric reference frame Type de document : Article/Communication Auteurs : Guy Wöppelmann Année de publication : 2009 Projets : 3-projet - voir note / Article en page(s) : 6 p. Note générale : bibliographie
The work was partly funded by Région Poitou‐Charentes, which provided a PhD fellowship for C. Letetrel, and by CNES which provided additional support via its TOSCA program.Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] analyse spatio-temporelle
[Termes IGN] déformation verticale de la croute terrestre
[Termes IGN] données marégraphiques
[Termes IGN] International Terrestrial Reference Frame
[Termes IGN] niveau de la merRésumé : (auteur) The results from a carefully implemented GPS analysis, using a strategy adapted to determine accurate vertical station velocities, are presented. The stochastic properties of our globally distributed GPS position time series were inferred, allowing the computation of reliable velocity uncertainties. Most uncertainties were several times smaller than the 1–3 mm/yr global sea level change, and hence the vertical velocities could be applied to correct the long tide gauge records for land motion. The sea level trends obtained in the ITRF2005 reference frame are more consistent than in the ITRF2000 or corrected for Glacial‐Isostatic Adjustment (GIA) model predictions, both on the global and the regional scale, leading to a reconciled global rate of geocentric sea level rise of 1.61 ± 0.19mm/yr over the past century in good agreement with the most recent estimates. Numéro de notice : A2009-587 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2009GL038720 Date de publication en ligne : 24/06/2009 En ligne : https://doi.org/10.1029/2009GL038720 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90911
in Geophysical research letters > vol 36 n° 12 (June 2009) . - 6 p.[article]Documents numériques
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Rates of sea‐level change ... - pdf éditeurAdobe Acrobat PDF
Titre : Error analysis of weekly station coordinates in the DORIS network Type de document : Article/Communication Auteurs : Simon D.P. Williams, Auteur ; Pascal Willis Année de publication : 2006 Article en page(s) : pp 525 - 539 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] bruit blanc
[Termes IGN] bruit rose
[Termes IGN] calcul d'erreur
[Termes IGN] données DORIS
[Termes IGN] International Terrestrial Reference Frame
[Termes IGN] méthode du maximum de vraisemblance (estimation)
[Termes IGN] série temporelle
[Termes IGN] station DORIS
[Termes IGN] traitement du signalRésumé : (Auteur) Twelve years of DORIS data from 31 selected sites of the IGN/JPL (Institut Géographique National/Jet Propulsion Laboratory) solution IGNWD05 have been analysed using maximum likelihood estimation (MLE) in an attempt to understand the nature of the noise in the weekly station coordinate time-series. Six alternative noise models in a total of 12 different combinations were used as possible descriptions of the noise. The six noise models can be divided into two natural groups, temporally uncorrelated (white) noise and temporally correlated (coloured) noise. The noise can be described as a combination of variable white noise and one of flicker, first-order Gauss–Markov or power-law noise. The data set as a whole is best described as a combination of variable white noise plus flicker noise. The variable white noise, which is white noise with variable amplitude that is a function of the weekly formal errors multiplied by an estimated scale factor, shows a dependence on site latitude and the number of DORIS-equipped satellites used in the solution. The latitude dependence is largest in the east component due to the near polar orbit of the SPOT satellites. The amplitude of the flicker noise is similar in all three components and equal to about 20 mm/year1/4. There appears to be no latitude dependence of the flicker noise amplitude. The uncertainty in rates (site velocities) after 12 years is just under 1 mm/year. These uncertainties are around 3–4 times larger than if only variable white noise had been assumed, i.e., no temporally correlated noise. A rate uncertainty of 1 mm/year after 12 years in the vertical is similar to that achieved using Global Positioning System (GPS) data but it takes DORIS twice as long to reach 1 mm/year than GPS in the horizontal. The analysis has also helped to identify sites with either anomalous noise characteristics or large noise amplitudes, and tested the validity of previously proposed discontinuities. In addition, several new offsets were found in the time-series that should be used or at least flagged in future work. Copyright Springer Numéro de notice : A2006-534 Affiliation des auteurs : IGN (1940-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-006-0056-6 En ligne : http://doi.org/10.1007/s00190-006-0056-6 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28257
in Journal of geodesy > vol 80 n° 8-11 (November 2006) . - pp 525 - 539[article]Exemplaires(2)
Code-barres Cote Support Localisation Section Disponibilité 266-06102 RAB Revue Centre de documentation En réserve L003 Disponible 266-06101 RAB Revue Centre de documentation En réserve L003 Disponible
