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Comparison of ground-based GPS precipitable water vapour to independent observations and NWP model reanalyses over Africa / Olivier Bock in Quarterly Journal of the Royal Meteorological Society, vol 133 n° 629 (Octobre 2007 part B)
[article]
Titre : Comparison of ground-based GPS precipitable water vapour to independent observations and NWP model reanalyses over Africa Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Marie-Noëlle Bouin , Auteur ; Andrea Walpersdorf, Auteur ; Jean-Philippe Lafore, Auteur ; Serge Janicot, Auteur ; Françoise Guichard, Auteur ; Anna Agusti-Panareda, Auteur Année de publication : 2007 Article en page(s) : pp 2011 - 2027 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique (géographie physique)
[Termes IGN] analyse comparative
[Termes IGN] cohérence des données
[Termes IGN] mousson
[Termes IGN] vapeur d'eauRésumé : (auteur) This study aims at assessing the consistency between different precipitable water vapour (PWV) datasets over Africa (between 35°N and 10°S). This region is characterized by large spatial and temporal variability of humidity but also by the scarcity of its operational observing network, limiting our knowledge of the hydrological cycle. We intercompare data from observing techniques such as ground-based Global Positioning System (GPS), radiosondes, AERONET sun photometers and SSM/I, as well as reanalyses from European Centre for Medium-Range Weather Forecasts (ERA-40) and National Center for Environmental Prediction (NCEP2). The GPS data, especially, are a new source of PWV observation in this region. PWV estimates from nine ground-based GPS receivers of the international GPS network data are used as a reference dataset to which the others are compared. Good agreement is found between observational techniques, though dry biases of 12–14% are evidenced in radiosonde data at three sites. Reasonable agreement is found between the observational datasets and ERA-40 (NCEP2) reanalyses with maximum bias ⩽9% (14%) and standard deviation ⩽17% (20%). Since GPS data were not assimilated in the ERA-40 and NCEP2 reanalyses, they allow for a fully independent validation of the reanalyses. They highlight limitations in the reanalyses, especially at time-scales from sub-daily to periods of a few days. This work also demonstrates the high potential of GPS PWV estimates over Africa for the analysis of the hydrological cycle, at time-scales ranging between sub-diurnal to seasonal. Such observations can help studying atmospheric processes targeted by the African Monsoon Multidisciplinary Analysis project. Numéro de notice : A2007-690 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1002/qj.185 Date de publication en ligne : 20/09/2007 En ligne : https://doi.org/10.1002/qj.185 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102776
in Quarterly Journal of the Royal Meteorological Society > vol 133 n° 629 (Octobre 2007 part B) . - pp 2011 - 2027[article]Assessment of GPS data for meteorological applications over Africa: Study of error sources and analysis of positioning accuracy / Andrea Walpersdorf in Journal of Atmospheric and Solar-Terrestrial Physics, vol 69 n° 12 (August 2007)
[article]
Titre : Assessment of GPS data for meteorological applications over Africa: Study of error sources and analysis of positioning accuracy Type de document : Article/Communication Auteurs : Andrea Walpersdorf, Auteur ; Marie-Noëlle Bouin , Auteur ; Olivier Bock , Auteur ; Erik Doerflinger, Auteur Année de publication : 2007 Article en page(s) : pp 1312 - 1330 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique tropicale
[Termes IGN] données météorologiques
[Termes IGN] mousson
[Termes IGN] précision du positionnement
[Termes IGN] retard troposphérique zénithal
[Termes IGN] vapeur d'eauRésumé : (auteur) The aim of this study is to assess the availability and quality of data from the International GNSS Service (IGS) Global Positioning System (GPS) network in Africa, especially for retrieving zenith tropospheric delay (ZTD), from which precipitable water vapour (PWV) can be derived, in view of application to the African Monsoon Multidisciplinary Analysis (AMMA) project. Three major error sources for the GPS data analysis evaluating PWV in Africa are the accuracy of the satellite orbits, the correction for the radio delay induced by the ionosphere and the vertical site displacements due to ocean loading. The first part of this study examines these error sources and the validity of GPS data for meteorological applications in Africa in dedicated analyses spanning the year 2001. These analyses were performed using the IGS precise orbits. Weak degradation of baseline precision with increasing baseline lengths suggests that the average orbital error is not limiting the GPS analysis in Africa. The impact of the ionosphere has been evaluated during a maximum of solar activity in 2001. The loss of L2 data has actually been observed. It amounts to 2% on average for 2001, with maxima of 8% during magnetic storm events. A slight decrease in formal accuracy of ZTD seems to be related to the loss of L2 data at the end of the day. This indicates that scintillation effects are present in the GPS observations but however are not a major limitation. The impact of ocean loading is found to be significant on ZTD estimates (up to ±2 mm in equivalent PWV). The use of a proper ocean loading model eliminates this effect.
The second aspect of this study concerns the IGS analysis quality for the African stations. The accuracy has been assessed through position dispersion between individual solutions and the most recent version of the IGS combined solution IGb00, and residuals from the transformation of the IGS combined solution into the International Terrestrial Reference Frame 2005. The positioning performance of the IGS analysis is consistent with an accuracy in ZTD of ±6 mm (±1 mm in PWV), as requested for meteorological applications such as planned in AMMA.Numéro de notice : A2007-672 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.jastp.2007.04.008 Date de publication en ligne : 08/05/2007 En ligne : https://doi.org/10.1016/j.jastp.2007.04.008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102771
in Journal of Atmospheric and Solar-Terrestrial Physics > vol 69 n° 12 (August 2007) . - pp 1312 - 1330[article]Multiscale analysis of precipitable water vapor over Africa from GPS data and ECMWF analyses / Olivier Bock in Geophysical research letters, vol 34 n° 9 (16 May 2007)
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Titre : Multiscale analysis of precipitable water vapor over Africa from GPS data and ECMWF analyses Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Françoise Guichard, Auteur ; Serge Janicot, Auteur ; Jean-Philippe Lafore, Auteur ; Marie-Noëlle Bouin , Auteur ; Benjamin Sultan, Auteur Année de publication : 2007 Projets : 1-Pas de projet / Article en page(s) : 6 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique (géographie physique)
[Termes IGN] analyse multiéchelle
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] précipitation
[Termes IGN] vapeur d'eauRésumé : (auteur) This is the first climatological analysis of precipitable water vapor (PWV) from GPS data over Africa. The data reveal significant modulations and variability in PWV over a broad range of temporal scales. GPS PWV estimates are compared to ECMWF reanalysis ERA40. Both datasets show good agreement at the larger scales (seasonal cycle and inter‐annual variability), driven by large scale moisture transport. At intra‐seasonal (15–40 days) and synoptic (3–10 days) scales, strong PWV modulations are observed from GPS, consistently with ECMWF analysis. They are shown to be correlated with convection and the passage of equatorial waves and African Easterly waves. The high‐frequency GPS observations also reveal a significant diurnal cycle in PWV, which magnitude and spectral content depends strongly on geographic location and shows a seasonal modulation. The diurnal cycle of PWV is poorly represented in ERA40 reflecting weaknesses in the water cycle of global circulation models at this timescale. Numéro de notice : A2007-682 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2006GL028039 Date de publication en ligne : 09/05/2007 En ligne : https://doi.org/10.1029/2006GL028039 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95742
in Geophysical research letters > vol 34 n° 9 (16 May 2007) . - 6 p.[article]Diurnal Cycle of Water Vapor as Documented by a Dense GPS Network in a Coastal Area during ESCOMPTE IOP2 / Sophie Bastin in Journal of Applied Meteorology and Climatology, vol 46 n° 2 (February 2007)
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Titre : Diurnal Cycle of Water Vapor as Documented by a Dense GPS Network in a Coastal Area during ESCOMPTE IOP2 Type de document : Article/Communication Auteurs : Sophie Bastin, Auteur ; Cédric Champollion, Auteur ; Olivier Bock , Auteur ; Philippe Drobinski, Auteur ; Frédéric Masson, Auteur Année de publication : 2007 Article en page(s) : pp 167 - 182 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] vapeur d'eauRésumé : (auteur) Global positioning system (GPS) data from a dense network have been used for the analysis of the diurnal cycle of water vapor over Marseille, France, during the second intensive observation period (IOP2; 21–26 June 2001) of the Expérience sur Sites pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d’Emission (ESCOMPTE) field experiment. Both tomographic analyses and integrated water vapor (IWV) contents from GPS have been used, in addition to wind profiler data and surface observations. Tomographic analysis of data from the dense GPS network and radiosondes provided the continuous temporal evolution of the vertical distribution of water vapor over the city of Marseille. The city is located on the shore of the Mediterranean Sea in southeastern France and is often under the influence of sea-breeze effects. Two different layers of breeze circulation are identified: a shallow sea breeze, blowing perpendicular to the local coastline, and a deep sea breeze, induced by the regional temperature gradient between sea and land. The origin of water vapor is shown to be mainly due to the advection of marine moist air by these sea-breeze circulations. However, the diurnal cycle of water vapor over Marseille is strongly influenced by the synoptic situation, which changes during the IOP2 (between a northerly mistral in the early stage of the IOP and an easterly wind at the end). It is shown that vertical profiles from tomographic analyses (combined with wind profiler data) allow for a proper interpretation of the diurnal cycle observed in IWV. Two-dimensional maps of IWV are also shown to complement the description of the horizontal advection of moisture by the different circulation regimes. Numéro de notice : A2007-678 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1175/JAM2450.1 En ligne : https://doi.org/10.1175/JAM2450.1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102779
in Journal of Applied Meteorology and Climatology > vol 46 n° 2 (February 2007) . - pp 167 - 182[article]Mapping carbon and water vapor fluxes in a chaparral ecosystem using vegetation indices derived from AVIRIS / D.A. Fuentes in Remote sensing of environment, vol 103 n° 3 (15 August 2006)
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Titre : Mapping carbon and water vapor fluxes in a chaparral ecosystem using vegetation indices derived from AVIRIS Type de document : Article/Communication Auteurs : D.A. Fuentes, Auteur ; John A. Gamon, Auteur ; et al., Auteur Année de publication : 2006 Article en page(s) : pp 312 - 323 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection
[Termes IGN] analyse diachronique
[Termes IGN] Californie (Etats-Unis)
[Termes IGN] circulation atmosphérique
[Termes IGN] dioxyde de carbone
[Termes IGN] données de terrain
[Termes IGN] écosystème
[Termes IGN] image AVIRIS
[Termes IGN] image hyperspectrale
[Termes IGN] indice de végétation
[Termes IGN] réflectance spectrale
[Termes IGN] sécheresse
[Termes IGN] vapeur d'eauRésumé : (Auteur) Using simple models derived from spectral reflectance, we mapped the patterns of ecosystem CO2 and water fluxes in a semi-arid site in southern California during a period of extreme disturbance, marked by drought and fire. Employing a combination of low (not, vert, similar 2 km) and high (not, vert, similar 16 km) altitude images from the hyperspectral Airborne Visible Infrared Imaging Spectrometer (AVIRIS), acquired between April 2002 and September 2003, and ground data collected from an automated tram system, several vegetation indices were calculated for Sky Oaks field station, a FLUXNET and SpecNet site located in northern San Diego County (CA, USA). Based on the relationships observed between the fluxes measured by the eddy covariance tower and the vegetation indices, net CO2 and water vapor flux maps were derived for the region around the flux tower. Despite differences in the scale of the images (from not, vert, similar 2 m to 16 m pixel size) as well as marked differences in environmental conditions (drought in 2002, recovery in early 2003, and fire in mid 2003), net CO2 and water flux modeled from AVIRIS-derived reflectance indices (NDVI, PRI and WBI) effectively tracked changes in tower fluxes across both drought and fire, and readily revealed spatial variation in fluxes within this landscape. After an initial period of net carbon uptake, drought and fire caused the ecosystem to lose carbon to the atmosphere during most of the study period. Our study shows the power of integrating optical and flux data in LUE models to better understand factors driving surface-atmosphere carbon and water vapor flux cycles, one of the main goals of SpecNet. Numéro de notice : A2006-333 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2005.10.028 En ligne : https://doi.org/10.1016/j.rse.2005.10.028 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28057
in Remote sensing of environment > vol 103 n° 3 (15 August 2006) . - pp 312 - 323[article]A new method to determine near surface air temperature from satellite observations / Ranjit Singh in International Journal of Remote Sensing IJRS, vol 27 n°12-13-14 (July 2006)PermalinkAssessment of the potential of MERIS near-infrared water vapour products to correct ASAR interferometric measurements / Z. Li in International Journal of Remote Sensing IJRS, vol 27 n°1-2 (January 2006)PermalinkApplication of an automated cloud-tracking algorithm on satellite imagery for tracking and monitoring small mesoscale convective cloud systems / H. Feidas in International Journal of Remote Sensing IJRS, vol 26 n° 8 (April 2005)PermalinkRegional simulation of ecosystem CO2 and water vapor exchange for agricultural land using NOAA AVHRR and Terra MODIS satellite data: Application to Zealand, Denmark / Rasmus M. Houborg in Remote sensing of environment, vol 93 n° 1 (30/10/2004)PermalinkSatellite constellation with direct radio measurements for atmospheric studies : WATS mission case / G. Alberti in International Journal of Remote Sensing IJRS, vol 25 n° 18 (September 2004)PermalinkNighttime polar cloud detection with MODIS / Y. Liu in Remote sensing of environment, vol 92 n° 2 (15/08/2004)PermalinkMapping the atmospheric water vapor by integrating microwave radiometer and GPS measurements / P. Basili in IEEE Transactions on geoscience and remote sensing, vol 42 n° 8 (August 2004)PermalinkGPS water vapor project associated to the ESCOMPTE programme: description and first results of the field experiment / Olivier Bock in Physics and chemistry of the Earth (A/B/C), vol 29 n° 2-3 ([01/03/2004])PermalinkGPS based determination of the integrated and spatially distributed water vapor in the troposphere / Marc Troller (2004)PermalinkRetrieval of atmospheric water vapour using a ground-based single-channel microwave radiometer / P. Jarlemark in International Journal of Remote Sensing IJRS, vol 24 n° 19 (October 2003)PermalinkDéveloppement d'un lidar Raman pour le sondage de la vapeur d'eau et la correction des délais troposphériques en GPS / Olivier Bock in Bulletin d'information scientifique et technique de l'IGN, n° 74 (mars 2003)PermalinkRetrievals of low integrated water vapor using MIR and SSM/T-2 measurements / J.R. Wang in IEEE Transactions on geoscience and remote sensing, vol 41 n° 3 (March 2003)PermalinkCloud and aerosol properties, precipitable water, and profiles of temperature and water vapor from MODIS / M.D. King in IEEE Transactions on geoscience and remote sensing, vol 41 n° 2 (February 2003)PermalinkImpact of contextual information integration on pixel fusion / Sophie Fabre in IEEE Transactions on geoscience and remote sensing, vol 40 n° 9 (September 2002)PermalinkPermalinkSpatial and temporal distribution of atmospheric water vapor using space geodetic techniques / Lars Peter Kruse (2001)PermalinkSystème DORIS : applications scientifiques / Pascal Willis in XYZ, n° 73 (septembre - novembre 1997)PermalinkUtilisation de la méthode de positionnement satellitaire GPS pour la détermination précise des altitudes relatives et absolues / Erik Doerflinger (1997)PermalinkPermalinkAtmospheric water vapour over oceans from SSM-I measurements / P. Schluessel in International Journal of Remote Sensing IJRS, vol 11 n° 5 (May 1990)PermalinkAn International Conference on thermal sensing and imaging diagnostic applications, Thermosense XII [12] / S.A. Semanovich (1990)PermalinkSatellite-derived low-level atmospheric water vapour content from synergy of AVHRR with HIRS / P. Schluessel in International Journal of Remote Sensing IJRS, vol 10 n°4-5 (May 1989)PermalinkMethods to correct, for the tropospheric delay in satellite-Earth range measurements / Gunnar Elgered (04/11/1985)PermalinkSatellite Earth range measurements : correction of the excess path length due to atmospheric water vapour by ground based microwave radiometry / Gunnar Elgered (1985)Permalink