71 research outputs found

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    Ecological studies need accurate environmental data such as vegetation characterization, landscape structure and organization, to predict and explain the spatial distribution of biodiversity. Few ecological studies use remote sensing data to assess the biophysical or structural properties of vegetation to understand species distribution. To date, synthetic aperture radar (SAR) data have seldom been used for ecological applications. However, these sensors provide data allowing access to the inner structure of vegetation which is a key information in ecology. The objective of this article is to compare the predictive power of ecological habitat structure variables derived from a TerraSAR-X image, an aerial photograph and a SPOT-5 image for species distribution. The test was run with a hedgerow network in Brittany and assessed the spatial distribution of the forest ground carabid beetles which inhabit these hedgerows. The results confirmed that radar and optical images can be indifferently used to extract hedgerow network and derived landscape metrics (hedgerow density, network grain) useful to explain the spatial distribution of forest carabid beetles. In comparison with passive optical remotely sensed data, VHSR SAR images provide new data to characterize vegetation structure and more particularly hedgerow canopy cover, a variable known to explain the spatial distribution of carabid beetles in an agricultural landscape, but not yet quantified at a fine scale. The hedgerow canopy cover derived from the SAR image is a strong predictor of the abundance of forest carabid beetles at two scales i.e., a local scale and a landscape scale

    Evaluation des donnĂ©es de tĂ©lĂ©dĂ©tection pour l’identification et la caractĂ©risation des continuitĂ©s Ă©cologiques

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    Habitat fragmentation is now considered as one of the most serious threats to biodiversity, and a major cause of the current crisis of species extinction. In fragmented landscapes, movement is a key process for the survival of flora and fauna species. Movement is facilitated by a significant connectivity between landscape elements. Among elements that contribute to increase landscape connectivity, ecological corridors are particularly useful and effective. The main objective of this pHD is to evaluate the interest of the VHSR images to identify and characterize potential agricultural landscape elements of the ecological networks. We evaluated the potential of SAR images and the combined use of VHSR optical and radar data to characterize ecological continuities at a fine scale, both structural and functional points of view. Results show that radar images and especially a polarimetric indicator, the Shannon entropy, allow quantifying the canopy cover of hedges. This indicator was assessed from an ecologically point of view. In addition, we highlight the indicators, classification methods and key dates to map wetland vegetation types. An evaluation of the synergy of radar and optical images shows the usefulness of radar data for crops mapping. We also showed the contribution of radar time series for improving biological models that explain the biodiversity distribution in agricultural landscapes. Finally, we developed new connectivity metrics, which relevant from an ecological point of view, by integrating information derived from remote sensing dataLa fragmentation des habitats est aujourd’hui considĂ©rĂ©e comme l’une des plus sĂ©rieuses menaces sur la biodiversitĂ©, et une des causes majeures de la crise actuelle d’extinction des espĂšces. Dans les paysages fragmentĂ©s, le mouvement est un processus clĂ© pour la survie des espĂšces faunistiques et floristiques, celui-ci Ă©tant facilitĂ© par une connectivitĂ© importante entre les Ă©lĂ©ments du paysage. Parmi les Ă©lĂ©ments qui concourent Ă  augmenter la connectivitĂ© du paysage, les corridors Ă©cologiques sont particuliĂšrement intĂ©ressants et efficaces. Le principal objectif de cette thĂšse est d’évaluer l’intĂ©rĂȘt des images THRS pour identifier et caractĂ©riser les Ă©lĂ©ments du paysage agricole potentiellement constitutifs des corridors Ă©cologiques. Pour cela, nous avons Ă©valuĂ© le potentiel des images RSO et de l’utilisation combinĂ©e des donnĂ©es optiques et radar THRS pour caractĂ©riser des continuitĂ©s Ă©cologiques Ă  Ă©chelle fine, tant d’un point de vue structurel que fonctionnel. Les rĂ©sultats montrent que les images radar et plus particuliĂšrement un indicateur polarimĂ©trique qui en est dĂ©rivĂ©, l’entropie de Shannon, permettent de quantifier le degrĂ© d’ouverture de la canopĂ©e des haies, indicateur qui a pu ĂȘtre Ă©valuĂ© d’un point de vue Ă©cologique. De plus, ils ont permis de mettre en Ă©vidence les indicateurs, les mĂ©thodes de classification et les dates clefs pour la cartographie des zones humides. Une Ă©valuation de la synergie d’images optiques et radar Ă  permis de montrer que les donnĂ©es radar permettent de cartographie des cultures. Nous avons Ă©galement montrĂ© l’apport des sĂ©ries temporelles d’images radar pour l’amĂ©lioration de modĂšles biologiques visant Ă  expliquer la distribution de la biodiversitĂ© dans les paysages agricoles. Enfin, nous avons pu dĂ©velopper de nouvelles mĂ©triques de connectivitĂ© en intĂ©grant des informations dĂ©rivĂ©es de donnĂ©es de tĂ©lĂ©dĂ©tection qui se sont avĂ©rĂ©es pertinentes d’un point de vue Ă©cologique

    Evaluation of remote sensing data for identification and characterization of ecological continuities

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    La fragmentation des habitats est aujourd’hui considĂ©rĂ©e comme l’une des plus sĂ©rieuses menaces sur la biodiversitĂ©, et une des causes majeures de la crise actuelle d’extinction des espĂšces. Dans les paysages fragmentĂ©s, le mouvement est un processus clĂ© pour la survie des espĂšces faunistiques et floristiques, celui-ci Ă©tant facilitĂ© par une connectivitĂ© importante entre les Ă©lĂ©ments du paysage. Parmi les Ă©lĂ©ments qui concourent Ă  augmenter la connectivitĂ© du paysage, les corridors Ă©cologiques sont particuliĂšrement intĂ©ressants et efficaces. Le principal objectif de cette thĂšse est d’évaluer l’intĂ©rĂȘt des images THRS pour identifier et caractĂ©riser les Ă©lĂ©ments du paysage agricole potentiellement constitutifs des corridors Ă©cologiques. Pour cela, nous avons Ă©valuĂ© le potentiel des images RSO et de l’utilisation combinĂ©e des donnĂ©es optiques et radar THRS pour caractĂ©riser des continuitĂ©s Ă©cologiques Ă  Ă©chelle fine, tant d’un point de vue structurel que fonctionnel. Les rĂ©sultats montrent que les images radar et plus particuliĂšrement un indicateur polarimĂ©trique qui en est dĂ©rivĂ©, l’entropie de Shannon, permettent de quantifier le degrĂ© d’ouverture de la canopĂ©e des haies, indicateur qui a pu ĂȘtre Ă©valuĂ© d’un point de vue Ă©cologique. De plus, ils ont permis de mettre en Ă©vidence les indicateurs, les mĂ©thodes de classification et les dates clefs pour la cartographie des zones humides. Une Ă©valuation de la synergie d’images optiques et radar Ă  permis de montrer que les donnĂ©es radar permettent de cartographie des cultures. Nous avons Ă©galement montrĂ© l’apport des sĂ©ries temporelles d’images radar pour l’amĂ©lioration de modĂšles biologiques visant Ă  expliquer la distribution de la biodiversitĂ© dans les paysages agricoles. Enfin, nous avons pu dĂ©velopper de nouvelles mĂ©triques de connectivitĂ© en intĂ©grant des informations dĂ©rivĂ©es de donnĂ©es de tĂ©lĂ©dĂ©tection qui se sont avĂ©rĂ©es pertinentes d’un point de vue Ă©cologique.Habitat fragmentation is now considered as one of the most serious threats to biodiversity, and a major cause of the current crisis of species extinction. In fragmented landscapes, movement is a key process for the survival of flora and fauna species. Movement is facilitated by a significant connectivity between landscape elements. Among elements that contribute to increase landscape connectivity, ecological corridors are particularly useful and effective. The main objective of this pHD is to evaluate the interest of the VHSR images to identify and characterize potential agricultural landscape elements of the ecological networks. We evaluated the potential of SAR images and the combined use of VHSR optical and radar data to characterize ecological continuities at a fine scale, both structural and functional points of view. Results show that radar images and especially a polarimetric indicator, the Shannon entropy, allow quantifying the canopy cover of hedges. This indicator was assessed from an ecologically point of view. In addition, we highlight the indicators, classification methods and key dates to map wetland vegetation types. An evaluation of the synergy of radar and optical images shows the usefulness of radar data for crops mapping. We also showed the contribution of radar time series for improving biological models that explain the biodiversity distribution in agricultural landscapes. Finally, we developed new connectivity metrics, which relevant from an ecological point of view, by integrating information derived from remote sensing dat
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