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Monitoring elevation variations in leaf phenology of deciduous broadleaf forests from SPOT/VEGETATION time-series / Dominique Guyon in Remote sensing of environment, vol 115 n° 2 ([15/02/2011])
[article]
Titre : Monitoring elevation variations in leaf phenology of deciduous broadleaf forests from SPOT/VEGETATION time-series Type de document : Article/Communication Auteurs : Dominique Guyon, Auteur ; Marie Guillot, Auteur ; Yann Vitasse, Auteur ; et al., Auteur Année de publication : 2011 Article en page(s) : pp 615 - 627 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Végétation
[Termes IGN] analyse des mélanges temporels
[Termes IGN] analyse diachronique
[Termes IGN] Fagus (genre)
[Termes IGN] feuillu
[Termes IGN] image SPOT-Végétation
[Termes IGN] indice de végétation
[Termes IGN] phénologie
[Termes IGN] Pyrénées (montagne)
[Termes IGN] Quercus (genre)
[Termes IGN] variation saisonnièreMots-clés libres : Phenology Leaf unfolding Deciduous forest Elevation VEGETATION Perpendicular vegetation index temporal unmixing Résumé : (auteur) In mountain forest ecosystems where elevation gradients are prominent, temperature gradient-based phenological variability can be high. However, there are few studies that assess the capability of remote sensing observations to monitor ecosystem phenology along elevation gradients, despite their relevance under climate change. We investigated the potential of medium resolution remotely sensed data to monitor the elevation variations in the seasonal dynamics of a temperate deciduous broadleaf forested ecosystem. Further, we explored the impact of elevation on the onset of spring leafing. This study was based on the analysis of multi-annual time-series of VEGETATION data acquired over the French Pyrenees Mountain Region (FPMR), in conjunction with simultaneous ground-based observations of leaf phenology made for two dominant tree species in the region (oak and beech). The seasonal variations in the perpendicular vegetation index (PVI) were analyzed during a five-year period (2002 to 2006). The five years of data were averaged into a one sole year in order to fill the numerous large spatio-temporal gaps due to cloud and snow presence – frequent in mountains – without altering the temporal resolution. Since a VEGETATION pixel (1 km²) includes several types of land cover, the broadleaf forest-specific seasonal dynamics of PVI was reconstructed pixel-by-pixel using a temporal unmixing method based on a non-parametric statistical approach. The spatial pattern of the seasonal response of PVI was clearly consistent with the relief. Nevertheless the elevational or geographic range of tree species, which differ in their phenology sensitivity to temperature, also has a significant impact on this pattern. The reduction in the growing season length with elevation was clearly observable from the delay in the increase of PVI in spring and from the advance of its decrease in the fall. The elevation variations in leaf flushing timing were estimated from the temporal change in PVI in spring over the study area. They were found to be consistent with those measured in situ (R2 > 0.95). It was deduced that, over FPMR, the mean delay of leaf flushing timing for every 100 m increase in elevation was estimated be approximately 2.3 days. The expected estimation error of satellite-based leaf unfolding date for a given elevation was approximately 2 days. This accuracy can be considered as satisfactory since it would allow us to detect changes in leafing timing of deciduous broadleaf forests with a magnitude equivalent to that due to an elevation variation of 100 m (2.3 days on average), or in other words, to that caused by a variation in the mean annual air temperature of 0.5 °C. Although averaging the VEGETATION data over five years led to a loss of interannual information, it was found to be a robust approach to characterise the elevation variations in spring leafing and its long-term trends. Numéro de notice : A2011-563 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2010.10.006 En ligne : https://doi.org/10.1016/j.rse.2010.10.006 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=74834
in Remote sensing of environment > vol 115 n° 2 [15/02/2011] . - pp 615 - 627[article]Evaluation of the impact of atmospheric pressure loading modeling on GNSS data analysis / Rolf Dach in Journal of geodesy, vol 85 n° 2 (February 2011)
[article]
Titre : Evaluation of the impact of atmospheric pressure loading modeling on GNSS data analysis Type de document : Article/Communication Auteurs : Rolf Dach, Auteur ; Johannes Böhm , Auteur ; Simon Lutz, Auteur ; Peter Steigenberger, Auteur ; Gerhard Beutler, Auteur Année de publication : 2011 Article en page(s) : pp 75 - 91 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] analyse de données
[Termes IGN] données GNSS
[Termes IGN] impact sur les données
[Termes IGN] International GNSS Service
[Termes IGN] série temporelle
[Termes IGN] signal GNSS
[Termes IGN] surcharge atmosphérique
[Termes IGN] variation saisonnièreRésumé : (Auteur) In recent years, several studies have demonstrated the sensitivity of Global Navigation Satellite System (GNSS) station time series to displacements caused by atmospheric pressure loading (APL). Different methods to take the APL effect into account are used in these studies: applying the corrections from a geophysical model on weekly mean estimates of station coordinates, using observation-level corrections during data analysis, or solving for regression factors between the station displacement and the local pressure. The Center for Orbit Determination in Europe (CODE) is one of the global analysis centers of the International GNSS Service (IGS). The current quality of the IGS products urgently asks to consider this effect in the regular processing scheme. However, the resulting requirements for an APL model are demanding with respect to quality, latency, and—regarding the reprocessing activities—availability over a long time interval (at least from 1994 onward). The APL model of Petrov and Boy (J Geophys Res 109:B03405, 2004) is widely used within the VLBI community and is evaluated in this study with respect to these criteria. The reprocessing effort of CODE provides the basis for validating the APL model. The data set is used to solve for scaling factors for each station to evaluate the geophysical atmospheric non-tidal loading model. A consistent long-term validation of the model over 15 years, from 1994 to 2008, is thus possible. The time series of 15 years allows to study seasonal variations of the scaling factors using the dense GNSS tracking network of the IGS. By interpreting the scaling factors for the stations of the IGS network, the model by (2004) is shown to meet the expectations concerning the order of magnitude of the effect at individual stations within the uncertainty given by the GNSS data processing and within the limitations due to the model itself. The repeatability of station coordinates improves by 20% when applying the effect directly on the data analysis and by 10% when applying a post-processing correction to the resulting weekly coordinates compared with a solution without taking APL into account. Numéro de notice : A2011-067 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-010-0417-z Date de publication en ligne : 22/10/2010 En ligne : https://doi.org/10.1007/s00190-010-0417-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30848
in Journal of geodesy > vol 85 n° 2 (February 2011) . - pp 75 - 91[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2011021 RAB Revue Centre de documentation En réserve L003 Disponible The large‐scale water cycle of the West African monsoon / Olivier Bock in Atmospheric Science Letters, vol 12 n° 1 (January - March 2011)
[article]
Titre : The large‐scale water cycle of the West African monsoon Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Françoise Guichard, Auteur ; Rémi Meynadier, Auteur ; Sébastien Gervois, Auteur ; Anna Agustí‐Panareda, Auteur ; Anton Beljaars, Auteur ; Aaron Boone, Auteur ; Mathieu Nuret, Auteur ; Jean-Luc Redelsperger, Auteur ; Pascal Roucou, Auteur Année de publication : 2011 Projets : AMMA & AMMA-2 / Janicot, Serge Article en page(s) : pp 51 - 57 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] analyse comparative
[Termes IGN] analyse diachronique
[Termes IGN] bilan hydrique
[Termes IGN] coordonnées GPS
[Termes IGN] données météorologiques
[Termes IGN] modèle météorologique
[Termes IGN] mousson
[Termes IGN] vapeur d'eau
[Termes IGN] variation saisonnièreRésumé : (Auteur) The vertically integrated water budget of West Africa is investigated with a hybrid dataset based on observational and modelling products elaborated by the African Monsoon Multidisciplinary Analyses (AMMA) and with several numerical weather prediction (NWP) products including the European Centre for Medium‐Range Weather Forecasts (ECMWF) AMMA reanalysis. Seasonal and intraseasonal variations are quantified over the period 2002–2007. Links between the budget terms are analyzed regionally, from the Guinean coast to the Sahel zone. Water budgets from the NWP systems are intercompared and evaluated against the hybrid dataset. Large deficiencies are evidenced in all the NWP products. Hypotheses are proposed about their origins and several improvements are foreseen. Copyright © 2010 Royal Meteorological Society. Numéro de notice : A2011-593 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1002/asl.288 Date de publication en ligne : 16/08/2010 En ligne : https://doi.org/10.1002/asl.288 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91516
in Atmospheric Science Letters > vol 12 n° 1 (January - March 2011) . - pp 51 - 57[article]West African Monsoon water cycle: 1. A hybrid water budget data set / Rémi Meynadier in Journal of geophysical research : Atmospheres, vol 115 n° D19 (2010)
[article]
Titre : West African Monsoon water cycle: 1. A hybrid water budget data set Type de document : Article/Communication Auteurs : Rémi Meynadier, Auteur ; Olivier Bock , Auteur ; Françoise Guichard, Auteur ; Aaron Boone, Auteur ; Pascal Roucou, Auteur ; Jean-Luc Redelsperger, Auteur Année de publication : 2010 Article en page(s) : 21 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] bilan hydrique
[Termes IGN] coordonnées GPS
[Termes IGN] données météorologiques
[Termes IGN] évapotranspiration
[Termes IGN] mousson
[Termes IGN] précipitation
[Termes IGN] teneur en vapeur d'eau
[Termes IGN] variation saisonnièreRésumé : (auteur) This study investigates the West African Monsoon water cycle with the help of a new hybrid water budget data set developed within the framework of the African Monsoon Multidisciplinary Analyses. Surface water and energy fluxes are estimated from an ensemble of land surface model simulations forced with elaborate precipitation and radiation products derived from satellite observations, while precipitable water tendencies are estimated from numerical weather prediction analyses. Vertically integrated atmospheric moisture flux convergence is estimated as a residual. This approach provides an advanced, comprehensive atmospheric water budget, including evapotranspiration, rainfall, and atmospheric moisture flux convergence, together with other surface fluxes such as runoff and net radiation. The annual mean and the seasonal cycle of the atmospheric water budget are presented and the couplings between budget terms are discussed for three climatologically distinct latitudinal bands between 6°N and 20°N. West Africa is shown to be alternatively a net source and sink region of atmospheric moisture, depending on the season (a source during the dry season and a sink during the wet season). Several limiting and controlling factors of the regional water cycle are highlighted, suggesting strong sensitivity to atmospheric dynamics and surface radiation. Some insight is also given into the underlying smaller‐scale processes. The relationship between evapotranspiration and precipitation is shown to be very different between the Sahel and the regions more to the south and partly controlled by net surface radiation. Strong correlations are found between precipitation and moisture flux convergence over the whole region from daily to interannual time scales. Causality is also established between monthly mean anomalies. Hence, precipitation anomalies are preceded by moisture flux convergence anomalies and followed by moisture flux divergence and evapotranspiration anomalies. The results are discussed in comparison to other studies. Numéro de notice : A2010-653 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2010JD013917 Date de publication en ligne : 01/10/2010 En ligne : https://doi.org/10.1029/2010JD013917 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91724
in Journal of geophysical research : Atmospheres > vol 115 n° D19 (2010) . - 21 p.[article]Voir aussiDocuments numériques
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West African Monsoon water cycle 1 - pdf éditeurAdobe Acrobat PDF Global gravity field determination using the GPS measurements made onboard the low Earth orbiting satellite CHAMP / Lars Prange (2010)
Titre : Global gravity field determination using the GPS measurements made onboard the low Earth orbiting satellite CHAMP Type de document : Rapport Auteurs : Lars Prange, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2010 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 81 Importance : 212 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-25-3 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] champ de pesanteur terrestre
[Termes IGN] données CHAMP
[Termes IGN] données GPS
[Termes IGN] Global Positioning System
[Termes IGN] gravimétrie spatiale
[Termes IGN] modèle de géopotentiel
[Termes IGN] orbite basse
[Termes IGN] orbitographie
[Termes IGN] positionnement par GPS
[Termes IGN] validation des données
[Termes IGN] variation saisonnièreIndex. décimale : 30.40 Géodésie physique Résumé : (Auteur) The major goal of this work was to to generate "the best possible" static CHAMP-only gravity field model using most of the openly available CHAMP data. Firstly we wanted to assess the full potential but also the limitations of CHAMP data and a CHAMP-like satellite mission for gravity field determination. Secondly we wanted to gain as much insight as possible in determining gravity fields (static and time variable) from space-based GNSS data in general, because several current and future satellite missions (dedicated to gravity field research, but also non-dedicated) equipped with GNSS receivers could benefit from improvements made here. We believe to have come close to achieving these goals by generating, validating, and publishing the static Earth gravity field models AIUB-CHAMPOIS, AIUB-CHAMP02S, and AIUB-CHAMP03S. Furthermore, the largest constituents of the seasonal gravity field variations could be retrieved from CHAMP data, as well. The Celestial Mechanics Approach (CMA) was successfully applied for gravity field determination. Note de contenu : 1 Introduction
2 Measuring the Earth's gravity field
2.1 Terrestrial geodesy
2.2 Satellite geodesy
2.2.1 Optical observations
2.2.2 Microwave methods
2.2.3 Satellite Laser Ranging (SLR)
2.2.4 Satellite altimetry
2.2.5 High-low SST of CHAMP
2.2.6 Low-low SST with GRACE
2.2.7 Satellite gradiometry with GOCE
3 Orbit determination and gravity field recovery
3.1 Least squares adjustment
3.1.1 Basic concept
3.1.2 LSA techniques
3.2 Coordinate systems
3.2.1 Geocentric quasi-inertial system
3.2.2 Earth-fixed coordinate system
3.2.3 Satellite-fixed coordinate system
3.3 Satellite orbits
3.3.1 Dynamic orbits
3.3.2 Reduced-dynamic orbits
3.3.3 Kinematic orbits
3.4 The equation of motion
3.5 Spherical harmonic representation of the gravitational potential
3.6 Orbit and gravity field determination
3.6.1 Numerical integration of the primary equations
3.6.2 Numerical integration of the variational equations
4. Global Positioning System - GPS
4.1 History
4.2 Basic measurement principle
4.3 GPS orbit constellation and satellites
4.4 GPS signals
4.5 Modeling GPS observables
4.5.1 Observation equations
4.5.2 Observation differences
4.5.3 Linear combinations
4.6 The International GNSS Service (IGS)
4.7 Bernese GPS Software (BSW)
5 Data processing
5.1 Generation of the A1UB-CHAMP01S gravity field model
5.1.1 Data Screening
5.1.2 Gravity field recovery
5.1.3 The AIUB-CHAMP01S gravity field model
5.2 Generation of the AIUB-CHAMP02S gravity field model
5.2.1 GNSS model changes
5.2.2 GPS orbit reprocessing
5.2.3 GPS satellite clock reprocessing
5.2.4 CHAMP orbit determination
5.2.5 AIUB-CHAMP02S gravity field recovery
5.2.6 The AIUB-CHAMP02S gravity field model
5.3 Generation of the AIUB-CHAMP03S gravity field model
5.3.1 Estimation of high-rate GPS satellite clock corrections
5.3.2 CHAMP orbit determination
5.3.3 Data screening and gravity field recovery
5.3.4 The AIUB-CHAMP03S gravity field model
6 Studies and experiments
6.1 Studies related to A1UB-C11AMP01S
6.1.1 Orbit modeling with arc-specific parameters
6.1.2 Modeling of non-gravitational perturbations with dynamic force models
6.1.3 Accelerometer data
6.1.4 Simulation study
6.1.5 Observation weights .
6.1.6 Influence of the a priori gravity field model
6.1.7 Screening the kinematic positions
6.1.8 Quality variations in monthly gravity field solutions
6.1.9 Summary and discussion of the IUB-CHAMPOlS-related studies
6.2 Experiments related to AIUB-CI1AMP02S
6.2.1 The impact of GNSS model changes
6.2.2 Inconsistency in the low degree harmonics
6.2.3 Simulation study
6.2.4 Latitude dependency of the observation scenario
6.2.5 Summary and conclusion of the AIUB-CHAMP02S-related studies
6.3 Experiments related to AIUB-CHAMP03S ..
6.3.1 Influence of empirical PCV-models on gravity field recovery using CHAMP GPS data ..
6.3.2 Elevation-dependent weighting
6.3.3 Observation sampling
6.3.4 Inter-epoch correlations of kinematic positions
6.3.5 Position differences vs. positions
6.3.6 Impact of observations of eclipsing GPS satellites on CHAMP gravity field recovery ...
6.3.7 Temporal variations of the Earth's gravity field
6.3.8 Recovery of the low degree harmonics
6.3.9 Summary of the experiments related to AIUB-CHAMP03S
7 Gravity field validation
7.1 Validation methods
7.1.1 Formal errors
7.1.2 Comparison with other gravity field models
7.1.3 Comparison with ground data
7.1.4 Altimetry data
7.1.5 Orbit determination
7.2 Validation of AIUB-CHAMP01S
7.2.1 Internal validation .
7.2.2 External validation
7.3 Validation of AIUB-CHAMP02S
7.3.1 Internal validation
7.3.2 External validation
7.4 Validation of AIUB-CHAMP03S
7.4.1 Internal validation
7.4.2 External validation
8 Summary and conclusionsNuméro de notice : 10370 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Rapport de recherche En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-81.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62409 Réservation
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