Manioc : Portail | resultats 21 - 40 pour la recherche: Soudan

Éditeur(s) : HAL CCSD Elsevier
Résumé : Vegetation phenology is the study of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and from radiometric data obtained with high accuracy from ground-based measurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the influence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the inflexion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE <= one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series is more likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. (C) 2013 Elsevier Inc. All rights reserved.
ISSN: 0034-4257

hal-01032407
https://hal.archives-ouvertes.fr/hal-01032407
DOI : 10.1016/j.rse.2013.01.010

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L'administration et les dépenses des colonies : réponse à M. Leroy-Beaulieu
Auteur(s) : Clavius-Marius, J. ( Conseiller Général )
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Ground-based network of NDVI measurements for tracking temporal dynamics of canopy structure and vegetation phenology in different biomes
Auteur(s) : Soudani, Kamel Hmimina, G. Delpierre, Nicolas Pontailler, J.-Y. Aubinet, Marc Bonal, Damien Caquet, B. De Grandcourt, A.
Auteurs secondaires : Ecologie Systématique et Evolution (ESE) ; Université Paris-Sud - Paris 11 (UP11) - AgroParisTech - Centre National de la Recherche Scientifique (CNRS) Agro-Bio Tech ; Université de Liège Ecologie et Ecophysiologie Forestières (EEF) ; Institut National de la Recherche Agronomique (INRA) - Université de Lorraine (UL) CRDPI ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement Ecologie des forêts de Guyane (ECOFOG) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) - Institut National de la Recherche Agronomique (INRA) - Université des Antilles et de la Guyane (UAG) - AgroParisTech - Centre National de la Recherche Scientifique (CNRS) Sol Agro et hydrosystème Spatialisation (SAS) ; Institut National de la Recherche Agronomique (INRA) - AGROCAMPUS OUEST Écologie fonctionnelle et physique de l'environnement (EPHYSE - UR1263) ; Institut National de la Recherche Agronomique (INRA) Centre d’Ecologie Fonctionnelle et Evolutive (CEFE) ; Institut de Recherche pour le Développement (IRD [France-Sud]) - Centre National de la Recherche Scientifique (CNRS) - Université de Montpellier (UM) - Institut national de la recherche agronomique [Montpellier] (INRA Montpellier) - École pratique des hautes études (EPHE) - Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro) - Université Paul-Valéry - Montpellier 3 (UM3) - Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)

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Voyage au Brésil : et contenant une carte et 16 gravures sur bois
Auteur(s) : Agassiz, Elizabeth Cabot Cary (1822-1907) Agassiz, Louis (1807-1873)
Auteurs secondaires : Belin de Launay, Jules (1814-1883) Vogeli, Félix
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Etudes et mémoires
Auteur(s) : Bassières, Gustave Eugène (1871-1931) Luc, M. Eberhardt, Philippe (1874-1942) Pobéguin, Henri (1856-1951) Henry, Yves Dubard, Marcel (1873-1914) Bonhoure, A. Noter, Raphaël de (1857-1936)
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La rivière et les forêts Guyanaises
Auteur(s) : Perret, Jacques
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L'Eldorado de Guyane réclame des chercheurs d'or mécanisés
Auteur(s) : Quris, Bernard
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Le calvaire d'un innocent ; n° 130
Auteur(s) : D' Arzac, Jules
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