Tropical forest phenology in French Guiana from MODIS time-series

ACL-11-12International audienceDespite a growing need for knowledge on how terrestrial ecosystems function, phenological studies are rather rare. This study characterizes the temporal evolution of forest covers in French Guiana using variations in the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite signal and vegetation indices, such as the Shortwave Infrared Water Stress Index and the Enhanced Vegetation Index. The principle consists of reconstructing a temporal cycle mosaiced from a 9-year database. Rather than extract the phenological information from each pixel, dynamics were extracted from homogeneous groups of forest pixels enabling the identification of different phenological phases in forest ecosystems. A north-south gradient of chlorophyll activity emerged. The further we moved to the south, the more forest groups consist of fast-growing and drought-tolerant species, whereas a north-south shift appeared at the start dates of phenological cycles. This is a promising approach that paves the way for a much deeper understanding of the mechanisms governing the rainforest in French Guiana, as well as the responses of the Amazon forest to climate change and drought in the long term

Validation of Copernicus High Resolution Layer on Imperviousness degree for 2006, 2009 and 2012

Pan-European High Resolution Layers (HRL) provide information on specific land cover characteristics, and are complementary to land cover / land use mapping such as in the CORINE land cover (CLC) datasets as part of the Land Monitoring Service (land.copernicus.eu) of the Copernicus programme, managed by the EC. The HRLs are produced from 20 m resolution satellite imagery through a combination of automatic processing and interactive rule-based classification. 5 themes have been identified so far, corresponding with the main themes from CLC, i.e. imperviousness, (the level of sealed soil), tree cover density and forest type, permanent grasslands, wetlands and water bodies. Pixels of 20 by 20 m are aggregated into 100 by 100 m grid cells for final products. The imperviousness layer was the first to be produced during 2006-2008 from multi-sensor, bi-temporal and ortho-rectified satellite imagery, the same as used for the CORINE Land Cover 2006 update. The production of IMD2006 covered 38 European countries (32 EEA Member States and 6 West-Balkan countries). Since the 2006 production, a time series of imperviousness has been produced for reference years 2009 and recently 2012 over the whole area covered by the 39 member and cooperating countries of the European Environment Agency (EEA) representing a total of 6 million km². For each year it is available as a raster layer with 20 m resolution. At the time of undertaking this study, the area delivered for the year 2012 was around 90% of the total area and the study is based on this areaJRC.D.5-Food Securit

Vegetation structure and greenness in Central Africa from Modis multi-temporal data.

8 pagesInternational audienceAfrican forests within the Congo Basin are generally mapped at a regional scale as broad-leaved evergreen forests, with the main distinction being between terra-firme and swamp forest types. At the same time, commercial forest inventories, as well as national maps, have highlighted a strong spatial heterogeneity of forest types. A detailed vegetation map generated using consistent methods is needed to inform decision makers about spatial forest organization and their relationships with environmental drivers in the context of global change. We propose a multi-temporal remotely sensed data approach to characterize vegetation types using vegetation index annual profiles. The classifications identified 22 vegetation types (six savannas, two swamp forests, 14 forest types) improving existing vegetation maps. Among forest types, we showed strong variations in stand structure and deciduousness, identifying (i) two blocks of dense evergreen forests located in the western part of the study area and in the central part on sandy soils; (ii) semi-deciduous forests are located in the Sangha River interval which has experienced past fragmentation and human activities. For all vegetation types enhanced vegetation index profiles were highly seasonal and strongly correlated to rainfall and to a lesser extent, to light regimes. These results are of importance to predict spatial variations of carbon stocks and fluxes, because evergreen/deciduous forests (i) have contrasted annual dynamics of photosynthetic activity and foliar water content and (ii) differ in community dynamics and ecosystem processes

Réalisation d'une chaîne de transmission numérique sous la plate forme ADS-Agilent

International audienceUne chaîne de transmission radionumérique WLAN complète est modélisée dans l'environnement de simulation ADS. L'exploitation pédagogique du modèle complet est particulièrement mise en évidence dans un contexte de formation supérieure à l'ingénierie des systèmes radiofréquences

Réalisation d'une chaîne de transmission numérique sous la plate forme ADS-Agilent

International audienceUne chaîne de transmission radionumérique WLAN complète est modélisée dans l'environnement de simulation ADS. L'exploitation pédagogique du modèle complet est particulièrement mise en évidence dans un contexte de formation supérieure à l'ingénierie des systèmes radiofréquences