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Hydrological deformation induced by the West African Monsoon : Comparison of GPS, GRACE and loading models / Samuel Nahmani in Journal of geophysical research : Solid Earth, Vol 117 n° B5 (May 2012)
[article]
Titre : Hydrological deformation induced by the West African Monsoon : Comparison of GPS, GRACE and loading models Type de document : Article/Communication Auteurs : Samuel Nahmani , Auteur ; Olivier Bock , Auteur ; Marie-Noëlle Bouin , Auteur ; Alvaro Santamaria Gomez, Auteur ; Jean-Paul Boy, Auteur ; Xavier Collilieux , Auteur ; Laurent Métivier , Auteur ; Isabelle Panet , Auteur ; Pierre Genthon, Auteur ; Caroline de Linage, Auteur ; Guy Wöppelmann , Auteur Année de publication : 2012 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] coordonnées GPS
[Termes IGN] déformation de la croute terrestre
[Termes IGN] données GRACE
[Termes IGN] données météorologiques
[Termes IGN] effet de charge
[Termes IGN] Gao
[Termes IGN] mousson
[Termes IGN] Niamey (Niger)
[Termes IGN] oscillation
[Termes IGN] Ouagadougou
[Termes IGN] station permanente
[Termes IGN] Tombouctou
[Termes IGN] variation saisonnièreRésumé : (Auteur) Three‐dimensional ground deformation measured with permanent GPS stations in West Africa was used for investigating the hydrological loading deformation associated with Monsoon precipitation. The GPS data were processed within a global network for the 2003–2008 period. Weekly station positions were retrieved with a repeatability (including unmodeled loading effects) of 1–2 mm in the horizontal components and between 2.5 and 6 mm in the vertical component. The annual signal in the vertical component for sites located between 9.6°N and 16.7°N is in the range 10–15 mm. It is consistent at the 3 mm‐level with the annual regional‐scale loading deformations estimated from GRACE satellite products and modeled with a combination of hydrological, atmospheric, and nontidal oceanic models. An additional 6 month transient signal was detected in the vertical component of GPS estimates at most of the West African sites. It takes the form of an oscillation occurring between September and March, and reaching a maximum amplitude of 12–16 mm at Ouagadougou (12.5°N). The analysis of in situ hydro‐geological data revealed a strong coincidence between this transient signal and peak river discharge at three sites located along the Niger River (Timbuktu, Gao, and Niamey). At Ouagadougou, a similar coincidence was found with the seasonal variations of the water table depth. We propose a mechanism to account for this signal that involves a sequence of swelling/shrinking of clays combined with local loading effects associated with flooding of the Niger River. Numéro de notice : A2012-753 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2011JB009102 Date de publication en ligne : 12/05/2012 En ligne : https://doi.org/10.1029/2011JB009102 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91470
in Journal of geophysical research : Solid Earth > Vol 117 n° B5 (May 2012)[article]Study of seasonal-scale atmospheric water cycle with ground-based GPS receivers, radiosondes and NWP models over Morocco / Achraf Koulali in Atmospheric Research, vol 104 - 105 (February 2012)
[article]
Titre : Study of seasonal-scale atmospheric water cycle with ground-based GPS receivers, radiosondes and NWP models over Morocco Type de document : Article/Communication Auteurs : Achraf Koulali, Auteur ; Driss Ouazar, Auteur ; Olivier Bock , Auteur ; Abdelali Fadil, Auteur Année de publication : 2012 Article en page(s) : pp 273 - 291 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Canaries
[Termes IGN] circulation atmosphérique
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] Maroc
[Termes IGN] précipitation
[Termes IGN] radiosondage
[Termes IGN] récepteur GPS
[Termes IGN] retard troposphérique zénithal
[Termes IGN] teneur en vapeur d'eau
[Termes IGN] variation saisonnièreRésumé : (Auteur) This study investigates the seasonal variation of precipitable water vapor, moisture transport and precipitation over Morocco and the Canary Islands using data from ground-based GPS receivers, radiosondes, GPCP and NCEP reanalysis II. In a first part, the datasets are inter-compared. Humidity biases are evidenced in both radiosonde observations (dry) and NCEP reanalysis (dry and wet) compared to GPS. Moisture transport and precipitation from the reanalysis and observations show a good agreement. Precipitable water shows a maximum in late summer whereas precipitation is peaking in winter and spring over Morocco. Moisture transport occurs preferentially in two layers, below and above 850 hPa. The monthly mean precipitable water variation over Morocco is controlled by the upper layer zonal and meridional moisture flux. Precipitation is rather controlled by the lower layer moisture flux and the upper layer meridional flux. The GPS tropospheric gradients show also a consistent seasonal evolution, which is explained by gradients both in the thickness of the troposphere and in the precipitable water vapor. Tropospheric gradients are correlated with moisture fluxes, mostly in the upper layer, and may therefore provide valuable information for meteorology and climatology. Numéro de notice : A2012-737 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.atmosres.2011.11.002 Date de publication en ligne : 13/11/2011 En ligne : https://doi.org/10.1016/j.atmosres.2011.11.002 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91460
in Atmospheric Research > vol 104 - 105 (February 2012) . - pp 273 - 291[article]
Titre : Water vapor tomography using global navigation satellites systems Type de document : Thèse/HDR Auteurs : Donat Perler, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2012 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 84 Importance : 188 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-30-7 Note générale : Bibliographie
Doctoral ThesisLangues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] atmosphère terrestre
[Termes IGN] données GNSS
[Termes IGN] données météorologiques
[Termes IGN] modélisation spatiale
[Termes IGN] positionnement par GNSS
[Termes IGN] rayonnement électromagnétique
[Termes IGN] temps réel
[Termes IGN] teneur en vapeur d'eau
[Termes IGN] tomographie par GPS
[Termes IGN] vapeur d'eauIndex. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (Auteur) Water vapor plays an important role in the atmosphere. It is involved in many atmospheric processes and is a major contributor to the atmospheric energy budget and as such is a key quantity in numerical weather prediction (NWP) models. In recent years, NWP models gain in importance in hazard mitigation. But to provide precise quantitative forecasts, especially with respect to precipitation, we need accurate knowledge of the water vapor distribution in the atmosphere. Ground-based Global Navigation Satellite System (GNSS) tomography is a technique which can provide highly resolved and accurate water vapor profiles in space and time.
The main objective of this thesis is to develop new tomographic algorithms which fulfill the requirements to assimilate refractivity measurements derived from GNSS into NWP models. A new tomography software called AWATOS 2 has been implemented. It is an assimilation system for point and integrated refractivity measurements. The tomographic model in AWATOS 2 is formulated as a Kalman filter and different voxel parameterizations are provided. The new trilinear and spline-based parameterizations allow a more accurate representation of the refractivity field without considerably increasing the number of unknowns. Advantages of these new parameterizations are a) more accurate results, b) point observations need not to be interpolated to the voxel centers and c) the tomographic solutions are at least C0-continuous in space. The stochastic prediction model implemented in AWATOS 2 relies on in-situ measurements and NWP model data. The prediction model is evaluated and adjusted with respect to data from the high-resolution NWP model COSMO-2 and from balloon soundings in Europe. In addition, AWATOS 2 provides a sophisticated simulation framework to carry out synthetic tests based on simple refractivity fields and on NWP model data. The algorithms of AWATOS 2 are assessed with synthetic tests and with real data in a longterm study using one year of data. The synthetic tests have confirmed the theoretical properties of the model such as a bias-free solution in case of bias-free input data, fast convergence rates, and the capability to resolve vertical structures in the wet refractivity field. In the long-term study, a root-mean-square (RMS) error of 3.0 ppm (0.4 gm3 absolute humidity) is achieved with respect to the NWP model COSMO-7. The investigations have shown that the newly introduced voxel parameterizations lead to significantly more accurate results than the classical constant parameterization.
The improvements are about 15% with respect to balloon soundings and 5% with respect to NWP analysis data. The performance of the trilinear and spline-based parameterizations are similar. Further investigations have revealed the importance of a bias correction model. A newly developed bias correction model has decreased the RMS error with respect to the NWP model analysis from 4.9 ppm (0.7 gm3) to 3.0 ppm (0.4 gm3) using the spline parameterization. For the other parameterizations, the improvements are significantly smaller. The systematic differences corrected here are mainly caused by a) systematic differences between GPS tropospheric path delays and the NWP model data and b) by discretization errors. Another error source is related to the departure of the NWP model’s topography from the true one which can amount to several hundred meters in alpine areas. Investigations have shown that processes near the Earth’s surface have a strong impact on the wet refractivity. Therefore, differences between the true topography and that of the NWP model can cause substantial errors. This topic has to be addressed if GNSS observations are assimilated into NWP models in complex terrain. Considerable progress has been made in the field of low-cost GNSS receivers in recent years allowing to build dense networks at low costs. Furthermore, the existing GNSSs are improved and new ones are being launched. These developments offer new possibilities in GNSS tomography. With error analyses, the potential of such improvements for GNSS tomography have been investigated The use of GPS together with Galileo has the potential to improve the formal accuracy of the GNSS tomography by 10-15% compared to a GPS-only solution. In Switzerland, equipping the SwissMetNet with GNSS receivers would increase the number of GNSS stations from 31 to 91. This would improve the formal accuracy of the tomographic solution by about 20-25%. The investigations have shown that the improvements obtained by a more dense network and additional GNSSs are cumulative. Placing the stations on different altitudes and choosing locations with good satellite visibility are important to achieve accurate results and should be considered in the design of GNSS networks.
All investigations have demonstrated that accurate 4D distributions of the wet refractivity in the troposphere can be estimated with GNSS tomography. The work has also revealed the possibilities and limitations of GNSS tomography in view of the assimilation into NWP models and proposes solution strategies to overcome the limitations.Note de contenu : 1 Introduction
1.1 Significance of tropospheric water vapor measurements
1.2 A short review of the research in GNSS tomography
1.3 Objectives and structure of the thesis
2 Introduction to the propagation of radio waves in the atmosphere
2.1 Propagation of radio waves in the atmosphere
2.2 Modeling the path delay
3 GNSS tomography with the software package AWATOS 2
3.1 Overview of AWATOS 2
3.2 Preprocessing of GNSS double difference delays
3.3 Discretization of the refractivity field and parameterization
3.4 Modeling the refractivity field with the Kalman filter approach
3.5 Simulation capabilities in AWATOS 2
4 Overview of the data sets
4.1 GPS data
4.2 Balloon soundings
4.3 Synoptic network SwissMetNet
4.4 Numerical weather prediction model COSMO
5 Description of the wet refractivity field
5.1 Tempo-spatial variation of the wet refractivity field
5.2 Discretization Error
5.3 Representation of the discretization error .
5.4 Investigations of the process noise using a random walk model
5.5 Conclusions
6 Comparison of balloon sounding data and GNSS-derived zenith path delays
6.1 Error budget of meteorological sensors
6.2 Intercomparison between zenith path delays of different sources
6.3 Conclusions
7 Potential of new GNSSs and dense networks in view of GNSS tomography
7.1 Configurations
7.2 Methods
7.3 Results and discussion
7.4 Conclusions
8 Simulation-based evaluation of the new tomographic algorithms
8.1 Theoretical considerations of the resolvability of vertical structures
8.2 Experiments with simulated data
8.3 Conclusions
9 Evaluation of the GPS tomography with a long-term study
9.1 Configuration and evaluation methods
9.2 Results and discussion
9.3 Bias correction model and its evaluation
9.4 Conclusions
10 Conclusions
11 OutlookNuméro de notice : 15546 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-006875504 En ligne : http://dx.doi.org/10.3929/ethz-a-006875504 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62758 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 15546-01 30.84 Livre Centre de documentation Géodésie Disponible 4D GPS water vapor tomography: new parameterized approaches / Donat Perler in Journal of geodesy, vol 85 n° 8 (August 2011)
[article]
Titre : 4D GPS water vapor tomography: new parameterized approaches Type de document : Article/Communication Auteurs : Donat Perler, Auteur ; Alain Geiger, Auteur ; Fabian Peter Hurter, Auteur Année de publication : 2011 Article en page(s) : pp 539 - 550 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Alpes
[Termes IGN] coordonnées ellipsoïdales
[Termes IGN] distribution spatiale
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] filtre de Kalman
[Termes IGN] prédiction
[Termes IGN] réfraction atmosphérique
[Termes IGN] réfringence
[Termes IGN] signal GPS
[Termes IGN] Suisse
[Termes IGN] tomographie
[Termes IGN] troposphère
[Termes IGN] vapeur d'eau
[Termes IGN] voxelRésumé : (Auteur) Water vapor is a key variable in numerical weather prediction, as it plays an important role in atmospheric processes. Nonetheless, the distribution of water vapor in the atmosphere is observed with a coarse resolution in time and space compared to the resolution of numerical weather models. GPS water vapor tomography is one of the promising methods to improve the resolution of water vapor measurements. This paper presents new parameterized approaches for the determination of water vapor distribution in the troposphere by GPS. We present the methods and give first results validating the approaches. The parameterization of voxels (volumetric pixels) by trilinear and spline functions in ellipsoidal coordinates are introduced in this study. The evolution in time of the refractivity field is modeled by a Kalman filter with a temporal resolution of 30s, which corresponds to the available GPS-data rate. The algorithms are tested with simulated and with real data from more than 40 permanent GPS receiver stations in Switzerland and adjoining regions covering alpine areas. The investigations show the potential of the new parameterized approaches to yield superior results compared to the non parametric classical one. The accuracy of the tomographic result is quantified by the inter-quartile range (IQR), which is decreased by 10–20% with the new approaches. Further, parameterized voxel solutions have a substantially smaller maximal error than the non parameterized ones. Simulations show a limited ability to resolve vertical structures above the top station of the network with GPS tomography. Numéro de notice : A2011-359 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-011-0454-2 Date de publication en ligne : 08/03/2011 En ligne : https://doi.org/10.1007/s00190-011-0454-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31138
in Journal of geodesy > vol 85 n° 8 (August 2011) . - pp 539 - 550[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2011081 RAB Revue Centre de documentation En réserve L003 Disponible Estimating meteorological visibility using cameras: A probabilistic model-driven approach / Nicolas Hautière (2011)
Titre : Estimating meteorological visibility using cameras: A probabilistic model-driven approach Type de document : Article/Communication Auteurs : Nicolas Hautière, Auteur ; Raouf Babari, Auteur ; Eric Dumont, Auteur ; Roland Brémont, Auteur ; Nicolas Paparoditis , Auteur Editeur : Berlin, Heidelberg, Vienne, New York, ... : Springer Année de publication : 2011 Collection : Lecture notes in Computer Science, ISSN 0302-9743 num. 6495 Conférence : ACCV 2010, 10th Asian Conference on Computer Vision 08/11/2010 12/11/2010 Queenstown Nouvelle-Zélande Proceedings Springer Importance : pp 243 - 254 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image
[Termes IGN] données météorologiques
[Termes IGN] éclairement lumineux
[Termes IGN] modèle stochastique
[Termes IGN] projection Lambert
[Termes IGN] visibilitéRésumé : (auteur) Estimating the atmospheric or meteorological visibility distance is very important for air and ground transport safety, as well as for air quality. However, there is no holistic approach to tackle the problem by camera. Most existing methods are data-driven approaches, which perform a linear regression between the contrast in the scene and the visual range estimated by means of reference additional sensors. In this paper, we propose a probabilistic model-based approach which takes into account the distribution of contrasts in the scene. It is robust to illumination variations in the scene by taking into account the Lambertian surfaces. To evaluate our model, meteorological ground truth data were collected, showing very promising results. This works opens new perspectives in the computer vision community dealing with environmental issues. Numéro de notice : C2010-054 Affiliation des auteurs : MATIS+Ext (1993-2011) Thématique : IMAGERIE Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : 10.1007/978-3-642-19282-1_20 En ligne : https://doi.org/10.1007/978-3-642-19282-1_20 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=101400 Harmonisation des séries temporelles : Application en climatologie / Anonyme in Géomatique expert, n° 78 (01/01/2011)PermalinkInfrastructure de données spatiales et ingénierie territoriale : une approche empirique à partir du SIG Pyrénées / P. Lenormand in Géomatique expert, n° 78 (01/01/2011)PermalinkMesoscale water cycle within the West African Monsoon / Christophe Peugeot in Atmospheric Science Letters, vol 12 n° 1 (January - March 2011)PermalinkOperational meteorology in West Africa : observational networks, weather analysis and forecasting / Andreas H. Fink in Atmospheric Science Letters, vol 12 n° 1 (January - March 2011)PermalinkThe large‐scale water cycle of the West African monsoon / Olivier Bock in Atmospheric Science Letters, vol 12 n° 1 (January - March 2011)PermalinkThe water vapour intercomparison effort in the framework of the Convective and Orographically-induced Precipitation Study: airborne-to-ground-based and airborne-to-airborne lidar systems / Rohini Bhawar in Quarterly Journal of the Royal Meteorological Society, vol 137 n° S1 (January 2011)PermalinkWest African Monsoon water cycle: 1. A hybrid water budget data set / Rémi Meynadier in Journal of geophysical research : Atmospheres, vol 115 n° D19 (2010)PermalinkWest African Monsoon water cycle: 2. Assessment of numerical weather prediction water budgets / Rémi Meynadier in Journal of geophysical research : Atmospheres, vol 115 n° D19 (2010)PermalinkModélisation des retards troposphériques pour les observations GPS et impacts sur l'estimation de la hauteur ellipsoïdale / François Fund in XYZ, n° 123 (juin - août 2010)PermalinkGlobal 4DVAR assimilation and forecast experiments using AMSU observations over land. Part II: Impacts of assimilating surface-sensitive channels on the African monsoon during AMMA / Fatima Karbou in Weather and Forecasting, vol 25 n° 1 (February 2010)PermalinkDiurnal cycle of the intertropical discontinuity over West Africa analysed by remote sensing and mesoscale modelling / Bernhard Pospichal in Quarterly Journal of the Royal Meteorological Society, vol 136 n° S1 (January 2010)PermalinkTropical cyclone trend analysis using enhanced parallel coordinates and statistical analytics / C.A. Steed in Cartography and Geographic Information Science, vol 36 n° 3 (July 2009)PermalinkOn the late northward propagation of the West African monsoon in summer 2006 in the region of Niger/Mali / Philippe Drobinski in Journal of geophysical research : Atmospheres, vol 114 n° D9 (2009)PermalinkTesting of Global Pressure-Temperature (GPT) Model and Global Mapping Function (GMF) in GPS analyses / Jan Kouba in Journal of geodesy, vol 83 n° 3-4 (March - April 2009)PermalinkObjectifs terre / J.M. Besnier (2009)PermalinkRENECOFOR. Dix ans de suivi de la végétation forestière : aspects méthodologiques et évolution temporelle de la flore (1994/1995-2005) / Frédéric Archaux (2009)PermalinkSpatially explicit modeling of phosphorus emissions: integrating GIS and remote sensing for hydrological modelling / H. Klug in Geoinformatics, vol 11 n° 8 (01/12/2008)PermalinkCorrection of humidity bias for Vaïsala RS80 sondes during AMMA 2006 Observing Period / Mathieu Nuret in Journal of Atmospheric and Oceanic Technology, vol 25 n° 11 (November 2008)PermalinkSpatialisation de la température et des flux énergétiques de surface à partir des données satellitaires Landsat ETM+ / M. Mehor in Revue Française de Photogrammétrie et de Télédétection, n° 190 (Septembre 2008)PermalinkGMES : vers une plate-forme spatiale européenne / Vincent Habchi in Géomatique expert, n° 62 (01/05/2008)Permalink