Contribution of low resolution data to African savannas characterization

- In the context of international programs to understand the atmosphere-biosphere interface to model climatic changes. - Needs at a global level of information about surface parameters as surface roughtness, land cover, water availbalility, phenology, etc. - The objectives of this study is focus on: - the land cover characterization; - the spatial distribution of ecosystems. - The focus is done on the savannas and specially the west african savannas. - The study is done with low resolution remotely sensed data. (Résumé d'auteur

Contribution of NOAA- AVHRR data to African savan nahs Characterization

The Advanced Very High Resolution Radiometer (AVHRR) is currently used for vegetation monitoring. Information on the state and evolution of the vegetation cover on continental areas is routinely obtained from Global Vegetation Index data (GVI). In this paper some aspects of continental level, biome features were interpreted from a global scale GVI time series acquired with the NOAA/AVHRR between 1986 and 1990. A biome classification scheme for Africa is proposed. NOAA/AVHRR data were submitted to a cloud filtering algorithm, subsequently calibrated and corrected for atmospheric perturbations. Typical behaviour of Normalised Difference Vegetation Index (NDVI) temporal evolution derived from the AVHRR are classified, colour coded, and mapped to be compared with classical biome cartographic information. Analysis of the temporal GVI shows, that the spatial organisation of natural biomes in Africa changes within a single growing season. Transition zones between major ecological zones can clearly be identified. Furthermore, closer examination of GVI temporal variations, reveals year to year differences assumed to be the result of changes in landscape structure. Results illustrate that this approach is appropriate to describe vegetation temporal dynamics. The approach shows potential to describe climatic and human interactions with African biomes. In this paper results are presented and limitations will be discussed. (Résumé d'auteur

Mesurer l'état des forêts tropicales : observation par satellite [fiches de compétences forêts SIA 2011]

Un des outils utilisés au Cirad pour caractériser la forêt est la télédétection. A partir d'images satellite, l'activité photosynthétique est mesurée continuellement. De nombreuses informations peuvent être déduites de l'analyse de cette activité. Ici, ce sont les caractéristiques spatiales et temporelles des paysages forestiers qui sont cartographiées. En parallèle, les impacts humains sur la forêt sont mesurés afin d'évaluer les dégâts occasionnés lors des travaux miniers ou forestiers. (Résumé d'auteur

Forest degradation estimation using remote sensing: a case study on Central African Republic

Human activities within tropical rain forests provoke perturbations and degradation. The capacity to measure the extent of these damages is essential for calculating carbon emissions under the REDD+ process. Remote sensing is a powerful tool to provide such information (logging, mining, infrastructure building). Various techniques to identify and quantify forest degradation have been used so far. One step further is to link in-time degradation and past-time degradation to document the recovery of ecosystems after logging. For this, we propose a processing chain adapted to Landsat and Spot imageries. Post-processing is devoted to extract degradation information using specific algorithms. A spatial index, sized to low resolution radiometer, is implemented to render the actual and past degree of degradation. It is then related to continental land cover maps to get insight in the actual state of particular forest categories. This tool is developed in the framework of the CoForChange program (http://www.coforchange.eu/project) which general objective is to predict changes in forest and tree species distribution in the Congo Basin due to global change and to elaborate decision-making tools. The presentation is focused on an example in real time and in real size. It covers all the moist forest of Central African Republic at a yearly time-scale during ten years of Landsat images archive. (Résumé d'auteur

Monitoring a pioneer front using SPOT-VEGETATION time series

Since the 1960s, the Amazonian forest has been shrinking with the advance of primarily commercial cultivated areas. The pattern is being strengthened by high population growth and the migration of populations towards these newly deforested pioneer fronts. These trends are causing space to be appropriated to the detriment of forested areas. It has become essential to be able to locate areas on the pioneer front quickly and systematically in order to characterize new phases in advancing deforestation as they occur. However, satellite tools with high spatial resolution are not suited to monitoring of this type, as their temporal resolution is too broad and data processing is characteristically complex. Although low–resolution satellite images therefore seem more appropriate to these analyses, they can raise major problems when the target areas are very specific. In order to use imagery with low spatial resolution, such as SPOT-VEGETATION images, this study proposes a monitoring methodology based on a deforestation front of very small size. The method could be extrapolated to other deforestation fronts to investigate new areas to be monitored and thus establish diagnoses of the temporal dynamics of landscape transformation. (Résumé d'auteur

Sensoriamento remoto e gestão do teritorio : Localisação et indentificaçãi dos sitios de garimpo ilegais na Guiana Francesa

In the amazonian basin, the tropical humid forest covers the majority of the territory and has few infrastructure of access. In the context, many activities are made without being perceived by the coastal population. Thus, some of these activities are practiced totally out law. It is the case for the illegal gold mining which damages the environment and leads to a strong pollution of the rivers, with the use of bad technics and the eagerness caracteristic of the illegal exploitations. At the moment, the increase of the outlaw exploitations and the conflicts it generates with oficial exploitation's owners requires operational means of surveillance. In this article, it is proposed a tecnic based on satellital imagery with the creation of a detection filter. Strong and reliable, it remains with the problem of the clouds, important in tropical regions. Nervertheless, the possibility of obtaining regular informations could become a substancial oportunity for the management of the territory in French Guiana as in the others countries which encounter the same problem with gold mining. (Résumé d'auteur

Uso do sensoriamento remoto otico para a compreenção da dinâmica dos manguezais no contexto amazônico

The mangroves represent an important source of goods and services for many communites living on the intertropical coastal regions. The study of such an ecosystem is thus essential. But this vegetation grows in hard conditions with periodical tidal inundations. Moreover, from the Amapá to the Venezuela, the littoral suffers the "amazonian muds' dispersion system" which leads to rapid and dramatic changes of the coast. So, monitoring the amazonian mangrove requires frequent datas. The remote sensing becomes then essential to save human and material resources. It is presented here some applications of the remote sensing to the study of amazonian mangroves. Temporal analysis allows the reconstitution of the coastal history and the understanding of its evolution. It is also used to realize an original datation of the mangroves. Correlations between population's parameters as LAI and sprectral properties of SPOT images are made in order to couple a model of reflectance with a model of development. A filter for the detection of the regeneration zones in the gap is also presented. (Résumé d'auteur

FORESEEN : a forest and remote sensing exchanges network

The Guiana Shield in South America is one of the largest wild areas in the world. However, this area is currently facing unsustainable logging, poor and often illegal mining practices and agricultural activities. This paper presents a project aiming at: promoting capacity building and training of people from this area in remote sensing; preparing a vegetation map using low resolution data; and develop tools to estimate the impact of human activities on the forest using high resolution satellite imagery. The building of a network of trained experts in remote sensing is devoted to complete these objectives. (Résumé d'auteur