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Implémentation de l'intranet scientifique de l'OVSM basé sur des routines Matlab gérant un flux de données scientifiques géoréférencées et amélioration du traitement des données GPS / Benoit Costes (2009)
Titre : Implémentation de l'intranet scientifique de l'OVSM basé sur des routines Matlab gérant un flux de données scientifiques géoréférencées et amélioration du traitement des données GPS Type de document : Mémoire Auteurs : Benoit Costes , Auteur Editeur : Champs-sur-Marne : Ecole nationale des sciences géographiques ENSG Année de publication : 2009 Importance : 56 p. Format : 21 x 30 cm Note générale : Bibliographie
Rapport de projet pluridisciplinaire, cycle des ingénieurs diplômés de l'ENSG 2ème année (IT2)Langues : Français (fre) Descripteur : [Vedettes matières IGN] Géomatique
[Termes IGN] Apache (serveur)
[Termes IGN] campagne GPS
[Termes IGN] données géophysiques
[Termes IGN] GAMIT
[Termes IGN] interpréteur de commandes
[Termes IGN] intranet
[Termes IGN] Martinique
[Termes IGN] Matlab
[Termes IGN] Montagne pelée (volcan)
[Termes IGN] PERL
[Termes IGN] réseau géodésique spécifique
[Termes IGN] script CGI
[Termes IGN] site web
[Termes IGN] traitement de données GNSS
[Termes IGN] volcanIndex. décimale : PROJET Mémoires : Rapports de projet - stage des ingénieurs de 2e année Résumé : (Auteur) L'Observatoire Volcanologique et Sismologique de Martinique utilise pour gérer les données de ses différents réseaux, un outil fondamental : le WebObs. J'ai, en me basant sur des routines écrites pour l'Observatoire de Guadeloupe, développé cet intranet afin d'en faire un outil performant, gérant les échanges de formats de données diverses et variées, les sélections géographiques et temporelles et les visualisations de données géophysiques sous formes de graphes Matlab. Pour cela, j'ai été amené à apprendre de nouveaux langages, à me servir pleinement de l'OS Linux, à configurer un serveur Apache pour rendre exécutable les scripts CCI, et à manipuler près de 90 programmes PERL, 130 routines Matlab, et quelques scripts Shell. Je tiens à noter que durant plusieurs semaines, j'ai travaillé seul et en pleine autonomie. J'ai également planifié et participé à la campagne GPS de répétition de l'observatoire, sans oublier le déchargement et le traitement des mesures effectuées. Enfin, j'ai contribué à améliorer le traitement automatique des données du réseau GPS l'OVSM en installant Garnit. Cependant, je n'ai pas pu en effectuer tous les paramétrages, la nouvelle distribution de Linux nécessaire au fonctionnement du logiciel n'ayant pu être installée que trop peu de temps avant mon départ. Note de contenu : 1) Présentation du stage
1.1 Présentation de l'organisme d'accueil : l'Observatoire Volcanologique et Sismologique de Martinique
Les observatoires de l'IPGP
L'OVSM
1.2 Objectifs du stage
Analyse du besoin
La campagne GPS
Gamit
Le WebObs
1.3 Objectifs finaux
2) Le WebObs
2.1 Analyse technique
2.1.1 Le squelette du site
2.1.2 L'intranet de Guadeloupe : étude et comparaisons
2.1.3 Langages et composantes techniques du WebObs
Perl et CCI
Matlab
2.2 Préliminaires
2.2.1 Introduction aux langages Shell et Perl
2.2.2 Configuration du serveur Apache
2.3 Implémentation du WebObs
2.3.1 Première phase
Première architecture
Le fichier de configuration principal
PERL
2.3.2 Matlab. Seconde phase
Les fichiers de configuration
Nouvelles architecture
2.3.3 Développement
Aspect général
Carte des réseaux
Communiqués B3
Géochimie
Bulletins sismiques
Sécurité et permissions
Analyse et suivi des données sismologiques
2.4 Conclusion sur le WebObs
3) Gamit et la campagne GPS de répétition
3.1 Gamit
3.1.1 Présentation
3.1.2 Installation
3.1.3 Problèmes rencontrés
3.2 La campagne GPS de répétition
3.2.1 Présentation
3.2.2 Planification
Contraintes
Plan de campagne
Conclusion
3.2.3 La campagne et le traitement des données
Déroulement
Traitement des données
ConclusionNuméro de notice : 13858 Affiliation des auteurs : IGN (1940-2011) Thématique : GEOMATIQUE Nature : Mémoire de projet pluridisciplinaire Organisme de stage : Observatoire Volcanologique et Sismologique de Martinique OVSM Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=50168 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 13858-01 PROJET Livre Centre de documentation Travaux d'élèves Disponible Ionospheric modeling for precise GNSS applications / Y. Memarzadeh (2009)
Titre : Ionospheric modeling for precise GNSS applications Type de document : Monographie Auteurs : Y. Memarzadeh, Auteur Editeur : Delft : Netherlands Geodetic Commission NGC Année de publication : 2009 Collection : Netherlands Geodetic Commission Publications on Geodesy, ISSN 0165-1706 num. 71 Importance : 208 p. Format : 17 x 24 cm ISBN/ISSN/EAN : 978-90-6132-314-3 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] antenne GNSS
[Termes IGN] correction ionosphérique
[Termes IGN] double différence
[Termes IGN] modèle ionosphérique
[Termes IGN] positionnement différentiel
[Termes IGN] positionnement par GNSS
[Termes IGN] précision centimétrique
[Termes IGN] propagation du signal
[Termes IGN] propagation ionosphérique
[Termes IGN] simple différence
[Termes IGN] temps réel
[Termes IGN] teneur totale en électrons
[Termes IGN] traitement de données GNSSIndex. décimale : 30.61 Systèmes de Positionnement par Satellites du GNSS Résumé : (Auteur) The main objective of this thesis is to develop a procedure for modeling and predicting ionospheric Total Electron Content (TEC) for high precision differential GNSS applications. As the ionosphere is a highly dynamic medium, we believe that to have a reliable procedure it is necessary to transfer the high temporal resolution GNSS network data into the spatial domain. This objective led to the development of a recursive physics-based model for the regular TEC variations and an algorithm for real-time modeling of the medium-scale Traveling Ionospheric Disturbances (MS-TID). The research described in this thesis can roughly be divided into three parts.
The main application of these developments can be found in Network RTK. Network-RTK is a technique based on a network of reference receivers to provide cm-level positioning accuracy in real time for users in the field. To get centimeter accuracy after a short (minutes) initialization period the ionospheric delay for the user's receiver needs to be predicted very precisely between the ionospheric pierce points of the reference receivers at the double difference level. Having the cm-level accuracy in the ionospheric interpolation is crucial for the carrier phase ambiguity resolution by the user. To achieve high precision in the ionospheric interpolation, regular and irregular variability of TEC in time and space should be taken into account. The regular TEC variation, which can reach several hundreds TEC units, is mainly a function of solar zenith angle. The irregular (or non-repeatable) variations are mainly wavelike effects associated with Traveling Ionospheric Disturbances (TID).
Although TID effects on the TEC are of the order of 0.1 TEC unit, MS-TIDs, with a typical wavelength less than a few hundred kilometers, is one of the main obstacles for accurate spatial interpolation of ionospheric induced delays in a medium-scale reference GPS network. Since most of interpolation methods either use spatial linear (or quadratic) interpolation or fit a lower-order surface, the methods are not capable to model the phase-offset, caused by MS-TIDs, at distinct ionospheric pierce points. There are two major complications. Firstly, interpolation must be done at the double-difference level, which involves taking single differences between ionospheric delays for the same satellite between two different receivers, followed by differencing single differences for different satellites. This means that two different patches of the ionosphere are involved, each related to a different satellite, and each possibly associated with different TIDs. Secondly, for operational network RTK, a real-time strategy for TID detection and modeling is needed.
In the first part the performance of several empirical ionosphere models for the regular TEC variation, such as Klobuchar, NeQuick, and the IGS Global Ionosphere Maps (GIM) are studied in the mid-latitude region using GPS data. Our results show that the GIM was able to correct the absolute slant ionospheric delay to better than 80% under different geomagnetic conditions of the ionosphere. The NeQuick model, which performed better than the Klobuchar model, could correct about 60% of the slant ionospheric delay. NeQuick is a real-time ionospheric correction model for the future European Galileo navigation system. A key input parameter for NeQuick is the effective ionization parameter (Az), which will be provided as a second order polynomial in the Galileo broadcast message to single-frequency users. The coefficients of the polynomial will be estimated daily from at least 20 permanent Galileo monitoring stations. As Galileo is under development, we propose an alternative approach for estimating Az using Global Ionospheric Maps (GIM). The main advantages of the alternative approach over the standard approach are: (1) the alternative approach is more reliable, because, each IGS GIM is based on data of up to 300 GNSS stations world-wide and each IGS GIM is the combination of results of up to four analysis centers, (2) the coefficients are more representative for all regions on the world because they are computed from a world-wide grid instead of about 20 distinct locations, (3) with the alternative procedure it is possible to provide Az in a different representation, for instance using a higher order polynomial, grid, or other function types, and (4) the computational effort is much smaller assuming the IGS GIMs have already been computed.
In the second part a normal ionosphere is defined using Chapman's ion production theory to approximate the regular variability of the Earth's ionosphere. The normal ionosphere consists of lower and upper region. The lower region is formed in a photochemical equilibrium resulting in a Chapman layer. The upper region is formed in a diffusive equilibrium, whilst ignoring the geomagnetic field, resulting in a new Chapman like ionospheric layer. Integration of the continuity equation of the normal ionosphere over height leads to a Boundary Value Problem (BVP) for the temporal evolution of VTEC. Solution of the BVP results in a novel recursive model for the regular TEC variation as a function of solar zenith angle. The main motivation for developing this model is that the empirical models of the first part were either ill-suited or too complicated to model and predict the regular variation of TEC for high precision differential GNSS applications. The performance of the new model is tested at local and global scales using GIM. In general, despite the geomagnetic field was ignored, the cases analyzed show that the model gives a good overall representation of the regular variation of VTEC in the mid-latitude region under a geomagnetically quiet ionosphere. This is an important result that shows the potential of the model for a number of applications. Since the model has a recursive form it is ideally suited to use as time update equation in a dynamic data processing or Kalman filter. Another application is to use it for removing the geometry-dependent trend from time series of GPS-provided ionospheric delays to provide a pure TID observation, which is carried out in the third part of this thesis.
In the third part, a new algorithm for the real-time detection and modeling of MS-TID effects is developed. In order to eliminate effects from large-scale TIDs, the algorithm uses between-receiver single-difference (SD) ionospheric delays in a medium scale GPS network. Although single-differencing also eliminates to some extend the geometry-dependent trend, the remaining part cannot be neglected. In this thesis, we fit the SD data to the recursive model which was developed in the second part of the thesis. Any wavelike fluctuations in the data with respect to the model are assumed to be from MS-TID effects. The detrended SD data are the main input of the algorithm. The algorithm consists of six steps: initialization, detection, scraping, cross-correlation, parameter estimation, and ending. A MS-TID is assumed to be a planar longitudinal traveling wave with spatially independent amplitude that propagates in an ionospheric patch. All characteristic parameters of the MS-TID wave (e.g. period, phase velocity, propagation direction, and amplitude) are considered to be time dependent, while the Doppler-shift caused by the satellite motion is taken into account in the estimation step. The performance of the algorithm is tested with GPS data from a network. Although real TIDs are not perfect waves, the algorithm was able to model (in time and in space) the MS-TID to a large extend. The performance was found to be comparable with the Kriging interpolation method. This is an important first result, in part because these two methods are based on different principles, but also because there is still room for improvement in our algorithm. With our physics based model it is possible to avoid the planar wave approximation and take the phase-offset of the wave into account, something which is not possible with Kriging.Note de contenu : Curriculum Vitae Acknowledgments Notation and Symbols Acronyms
1 Introduction
1.1 Background
1.2 Research objectives
1.3 Outline of the thesis
1.4 Contributions of this research
2 The Earth's Atmosphere, Sun, and Geomagnetism
2.1 The Earth's Atmosphere .
2.1.1 Pressure, temperature and density variations
2.1.2 Diffusive equilibrium
2.1.3 Upper atmosphere .
2.2 The Sun
2.2.1 The Solar radiation
2.2.2 Variation of the radiation intensity
2.2.3 Solar radiations index (F10.7) .
2.3 Geomagnetism .
2.3.1 The earth's magnetic dipole field
2.3.2 The real geomagnetic field
2.3.3 Geomagnetic storm
2.3.4 Geomagnetic indices
3 Physics of the Earth's Ionosphere
3.1 Interaction of solar radiation with the Earth's upper atmosphere
3.2 Ionosphere formation theory
3.2.1 Plasma continuity equation
3.2.2 Ion production
3.2.3 Ion and electron disappearance .
3.2.4 Chapman layer
3.3 Transport process in the ionosphere .
3.3.1 Charged particle motion in a magnetic field .
3.3.2 Plasma diffusion .
3.3.3 Thermospheric wind .
3.3.4 Electromagnetic drift
3.4 Ionospheric stratification .
3.4.1 The D-Region
3.4.2 The E-Region
3.4.3 The F-Region
3.4.4 The topside region and the protonosphere .
3.4.5 Vertical electron density profile of the ionosphere
3.4.6 Characteristic parameters of the ionospheric regions
3.5 Spatial and temporal variability of the ionosphere
3.5.1 Regular variations
3.5.2 Geomagnetic regions .
3.6 Solar disturbances
3.6.1 Ionospheric disturbances .
3.6.2 Atmospheric gravity waves
3.6.3 Traveling ionospheric disturbances
4 Ionospheric delay measured from GNSS
4.1 Global Navigation Satellite Systems (GNSS) .
4.2 GNSS observation equations
4.2.1 Code or pseudo-range observation equation
4.2.2 Carrier beat phase observation equation
4.2.3 Simplifications of the observation equations
4.2.4 Tropospheric effects
4.3 Ionospheric propagation of GNSS signals .
4.3.1 Inhomogeneity of the ionosphere .
4.3.2 Dispersivity of the ionosphere .
4.3.3 Anisotropy of the ionosphere .
4.3.4 Ionospheric refractive index
4.3.5 Ionospheric first-, higher-order and bending effects . .
4.4 Ionospheric Total Electron Content (TEC)
4.4.1 A single-layer ionosphere approximation
4.4.2 Approximation of the higher-order and bending effects
4.5 Ionospheric models
4.5.1 Klobuchar model
4.5.2 Global Ionosphere Maps
4.6 Slant ionospheric delay measurements from GNSS
4.6.1 Network processing
4.6.2 Geometry-free linear combination 4.7 Summary
5 NeQuick 3D Ionospheric Electron Density Profiler
5.1 Ionospheric electron density model NeQuick
5.1.1 NeQuick model formulation for the bottom side (h < hmaXtF2)
5.1.2 NeQuick model formulation for the top side (hmax,F2 < /')
5.2 Characteristic parameters of the anchor points
5.2.1 Peak height of the F'2 region
5.2.2 Thickness parameters of the semi-Epstein layers
5.3 Providing the ionosonde parameters for NeQuick .
5.3.1 CCIR maps of /0F2 and M(3000)F2
5.3.2 Diagrammatic presentation of NeQuick
5.4 NeQuick for the Galileo navigation system
5.4.1 Effective Ionization Level (Az parameter) .
5.4.2 Estimation of the effective ionization level (nominal approach)
5.4.3 Improved version of NeQuick .
5.5 Estimation of the effective ionization level using GIM .
5.5.1 Estimation of the effective ionization level (alternative approach
5.5.2 Daily grid-based map of the effective ionization level
5.5.3 Az parameter for single point positioning .
5.6 Validation of the alternative approach .
5.6.1 Consistency of the approaches .
5.6.2 Modeling the spatial dependency of the Az parameter
5.6.3 Correlation between Az and F10.7
5.7 Performance of the NeQuick ionospheric model
5.7.1 Data specifications and processing
5.7.2 Comparison between the model errors .
5.8 Concluding remarks ..
6 Physics-Based Modeling of TEC
6.1 Normal ionosphere
6.1.1 Vertical electron density profile in the normal ionosphere . . . .
6.1.2 VTEC in the normal E-region .
6.1.3 VTEC in the normal F-region .
6.1.4 Combined VTEC of the normal ionosphere
6.1.5 Slant TEC in the normal ionosphere
6.2 Recursive model of VTEC in the normal ionosphere
6.2.1 Parametrization of the VTEC model .
6.2.2 Providing the model parameters
6.2.3 Functional model for estimating the parameters
6.2.4 Linearization of the functional model .
6.2.5 Least-squares solution of the model parameters
6.3 Performance of the VTEC model .
6.3.1 Local test of the VTEC model .
6.3.2 Global test of the VTEC model .
6.3.3 Applications of the VTEC model 6.4 Summary
7 Real-Time Modeling for Medium-Scale TID
7.1 Introduction
7.2 Medium-Scale Traveling Ionospheric Disturbances
7.3 Mechanical longitudinal wave equation
7.3.1 Traveling plane wave
7.3.2 Standing plane wave
7.4 GPS-provided TID observation .
7.4.1 Geometry-dependent trend of slant ionospheric delay
7.4.2 TID observation
7.4.3 Single-difference TID observation .
7.4.4 Double-difference TID observation .
7.5 TID observation equation .
7.5.1 Doppler-shift on TID observation .
7.6 Estimation of TID wave parameters
7.6.1 Period determination
7.6.2 TID wave vector determination
7.6.3 TID wave amplitude determination
7.7 Real-Time Medium-scale TID modeling
7.7.1 Initialization step
7.7.2 TID detection and scraping steps .
7.7.3 Cross correlation step .
7.7.4 TID parameter estimation .
7.7.5 TID ending .
7.7.6 Flowchart of the Real-Time TID modeling algorithm
7.7.7 Dependency on reference baseline .
7.7.8 Sensitivity to temporal resolution .
7.8 Implementation of the Real-Time TID modeling .
7.8.1 Case study: PRN 02
7.8.2 Case study: PRN 08
7.9 Conclusions and remarks
8 Conclusions and recommendations
8.1 Estimation of effective ionization for NeQuick .
8.2 Spatial and temporal variation of effective ionization level .
8.3 Performance of global TEC models
8.4 Model of temporal evolution of VTEC .
8.5 Modeling Medium-Scale Traveling Ionospheric Disturbances
Bibliography
IndexNuméro de notice : 15510 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62743 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15510-01 30.61 Livre Centre de documentation Géodésie Disponible
[article]
Titre : Orphéon : le réseau GPS haute qualité Type de document : Article/Communication Auteurs : Anonyme, Auteur Année de publication : 2009 Article en page(s) : pp 34 - 39 Langues : Français (fre) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] Orphéon
[Termes IGN] positionnement par GPS
[Termes IGN] traitement de données GNSSRésumé : (Auteur) Porté par la société Geodata Diffusion, le réseau Oorphéon se veut être, des réseaux GPS/GNSS permanents nationaux français, celui qui offre les meilleures prestations en terme de qualité de positionnement et de service. Pour atteindre cet objectif, ses gestionnaires ont déployé une infrastructure à la hauteur de leurs ambitions. Copyright CiMax Numéro de notice : A2009-047 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29677
in Géomatique expert > n° 66 (01/01/2009) . - pp 34 - 39[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 265-09011 RAB Revue Centre de documentation En réserve L003 Disponible Documents numériques
en open access
a2009-047_orpheon.pdfAdobe Acrobat PDF GNSS three carrier ambiguity resolution using ionosphere-reduced virtual signals / Y. Feng in Journal of geodesy, vol 82 n° 12 (December 2008)
[article]
Titre : GNSS three carrier ambiguity resolution using ionosphere-reduced virtual signals Type de document : Article/Communication Auteurs : Y. Feng, Auteur Année de publication : 2008 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] ambiguïté entière
[Termes IGN] correction ionosphérique
[Termes IGN] phase GNSS
[Termes IGN] positionnement cinématique en temps réel
[Termes IGN] positionnement par GNSS
[Termes IGN] résolution d'ambiguïté
[Termes IGN] signal GNSS
[Termes IGN] traitement du signalRésumé : (Auteur) This paper presents a general modeling strategy for ambiguity resolution (AR) and position estimation (PE) using three or more phase-based ranging signals from a global navigation satellite system (GNSS). The proposed strategy will identify three best “virtual” signals to allow for more reliable AR under certain observational conditions characterized by ionospheric and tropospheric delay variability, level of phase noise and orbit accuracy. The selected virtual signals suffer from minimal or relatively low ionospheric effects, and thus are known as ionosphere-reduced virtual signals. As a result, the ionospheric parameters in the geometry-based observational models can be eliminated for long baselines, typically those of length tens to hundreds of kilometres. The proposed modeling comprises three major steps. Step 1 is the geometry-free determination of the extra-widelane (EWL) formed between the two closest L-band carrier measurements, directly from the two corresponding code measurements. Step 2 forms the second EWL signal and resolves the integer ambiguity with a geometry-based estimator alone or together with the first EWL. This is followed by a procedure to correct for the first-order ionospheric delay using the two ambiguity-fixed widelane (WL) signals derived from the integer-fixed EWL signals. Step 3 finds an independent narrow-lane (NL) signal, which is used together with a refined WL to resolve NL ambiguity with geometry-based integer estimation and search algorithms. As a result, the above two AR processes performed with WL/NL and EWL/WL signals respectively, either in sequence or in parallel, can support real time kinematic (RTK) positioning over baselines of tens to hundreds of kilometres, thus enabling centimetre-to-decimetre positioning at the local, regional and even global scales in the future. Copyright Springer Numéro de notice : A2008-469 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-008-0209-x En ligne : https://doi.org/10.1007/s00190-008-0209-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29538
in Journal of geodesy > vol 82 n° 12 (December 2008)[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-08111 RAB Revue Centre de documentation En réserve L003 Disponible 266-08112 RAB Revue Centre de documentation En réserve L003 Disponible West African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA) / Olivier Bock in Journal of geophysical research : Atmospheres, vol 113 n° D21 (16 November 2008)
[article]
Titre : West African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA) Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Marie-Noëlle Bouin , Auteur ; Erik Doerflinger, Auteur ; Philippe Collard, Auteur ; Florian Masson, Auteur ; Rémi Meynadier, Auteur ; Samuel Nahmani , Auteur ; et al., Auteur Année de publication : 2008 Projets : AMMA & AMMA-2 / Janicot, Serge Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] circulation atmosphérique
[Termes IGN] données GPS
[Termes IGN] erreur systématique
[Termes IGN] humidité de l'air
[Termes IGN] modèle de simulation
[Termes IGN] mousson
[Termes IGN] phénomène atmosphérique
[Termes IGN] précipitation
[Termes IGN] vapeur d'eau
[Termes IGN] variation saisonnièreRésumé : (auteur) A ground-based GPS network has been established over West Africa in the framework of African Monsoon Multidisciplinary Analysis (AMMA) in tight cooperation between French and African institutes. The experimental setup is described and preliminary highlights are given for different applications using these data. Precipitable water vapor (PWV) estimates from GPS are used for evaluating numerical weather prediction (NWP) models and radiosonde humidity data. Systematic tendency errors in model forecasts are evidenced. Correlated biases in NWP model analyses and radiosonde data are evidenced also, which emphasize the importance of radiosonde humidity data in this region. PWV and precipitation are tightly correlated at seasonal and intraseasonal timescales. Almost no precipitation occurs when PWV is smaller than 30 kg m−2. This limit in PWV also coincides well with the location of the intertropical discontinuity. Five distinct phases in the monsoon season are determined from the GPS PWV, which correspond either to transition or stationary periods of the West African Monsoon system. They may serve as a basis for characterizing interannual variability. Significant oscillations in PWV are observed with 10- to 15-day and 15- to 20-day periods, which suggest a strong impact of atmospheric circulation on moisture and precipitation. The presence of a diurnal cycle oscillation in PWV with marked seasonal evolutions is found. This oscillation involves namely different phasing of moisture fluxes in different layers implying the low-level jet, the return flow, and the African Easterly Jet. The broad range of timescales observed with the GPS systems shows a high potential for investigating many atmospheric processes of the West African Monsoon. Numéro de notice : A2008-656 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2008JD010327 Date de publication en ligne : 05/11/2008 En ligne : https://doi.org/10.1029/2008JD010327 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=98266
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