193 research outputs found

    Spatial uncertainty effects on a species-landscape relationship model in ecology

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    In this study, we explore the effects of geometrical uncertainty in an existing species-landscape relationship model in the hoverfly communities. We also investigate how geometrical uncertainties affect a more complex model including both current forest patch features and past forest features. Because of a possible time-lag in biological responses to forest changes such as fragmentation, the historical dimension is added to the first model. The proposed approach relies on three spatial sources enabling to get forest fragments at different times: historical map (~1850), aerial black and white photographs (1954) and orthorectified photographs (2010). Firstly, we analyze the effect of the spatial data production method (manual versus automatic) on models using current forest patches only. Then, we build a more complex model including past changes in forest size. As previously, the effect of production-based uncertainty was assessed by comparing the models based on forests extracted manually and automatically. We address finally the impact of positional accuracy on the historical map by using a Monte Carlo simulation approach. Global results show that responses of the statistical models are strongly affected by spatial uncertainty in inputs

    Estimating taxonomic diversity and functional types of perennial forage grasses in mountain meadows: potentialities of Pléiades imagery

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    Estimating taxonomic diversity and functional types of perennial forage grasses in mountain meadows: potentialities of Pléiades imagery

    Discriminating small wooded elements in rural landscape from aerial photography: a hybrid pixel/object-based analysis approach

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    While small, fragmented wooded elements do not represent a large surface area in agricultural landscape, their role in the sustainability of ecological processes is recognized widely. Unfortunately, landscape ecology studies suffer from the lack of methods for automatic detection of these elements. We propose a hybrid approach using both aerial photographs and ancillary data of coarser resolution to automatically discriminate small wooded elements. First, a spectral and textural analysis is performed to identify all the planted-tree areas in the digital photograph. Secondly, an object-orientated spatial analysis using the two data sources and including a multi-resolution segmentation is applied to distinguish between large and small woods, copses, hedgerows and scattered trees. The results show the usefulness of the hybrid approach and the prospects for future ecological applications

    PrĂ©diction des services Ă©cosystĂ©miques dans les bois agricoles Ă  partir d’images hyperspectrales

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    Les services Ă©cosystĂ©miques sont devenus un enjeu social, Ă©cologique et Ă©conomique majeur dans le monde. Les forĂȘts des paysages agricoles offrent des services prĂ©cieux bien qu'ils soient souvent sous-estimĂ©s et mal utilisĂ©s. Cependant, une cartographie prĂ©cise de ces services Ă  grande Ă©chelle reste difficile. Des donnĂ©es de tĂ©lĂ©dĂ©tection permettent aujourd’hui d’envisager cette cartographie. Nous avons Ă©valuĂ© la contribution des indices de vĂ©gĂ©tation calculĂ©s Ă  partir d'images hyperspectrales Ă  haute rĂ©solution spatiale pour la prĂ©vision de services Ă©cosystĂ©miques par rapport aux rĂ©sultats fondĂ©es sur la couverture terrestre. 28 parcelles forestiĂšres ont Ă©tĂ© Ă©chantillonnĂ©es et des images hyperspectrales aĂ©roportĂ©es ont Ă©tĂ© acquises pour la zone d'Ă©tude, Ă  une rĂ©solution de 2 m. Habituellement, les indices de vĂ©gĂ©tation dĂ©rivĂ©s de l'hyperspectral Ă  l’échelle du paysage (buffer spatial autour de l’objet considĂ©rĂ©) sont rĂ©duits en utilisant des statistiques descriptives (moyenne, Ă©cart-type, valeurs minimales et maximales). Cependant, cette approche peut perdre beaucoup d'informations, en particulier Ă  l'Ă©chelle des paysages, oĂč plusieurs objets avec diffĂ©rentes signatures spectrales sont prĂ©sents. Nous proposons une description du paysage hyperspectral basĂ©e sur la rĂ©partition complĂšte des indices de vĂ©gĂ©tation Ă  travers les paysages. Nous avons utilisĂ© les modĂšles de mĂ©lange gaussien (GMM) pour modĂ©liser la distribution des pixels dans chaque paysage et introduit une distance L2 entre ces mĂ©langes. Cette distance est utilisĂ©e dans l’algorithme des plus proches voisins pour prĂ©dire les niveaux de services. La qualitĂ© des prĂ©dictions a Ă©tĂ© comparĂ©e entre trois reprĂ©sentations de paysage: occupation des sols, statistiques descriptives de donnĂ©es hyperspectrales et description de donnĂ©es hyperspectrales basĂ©es sur GMM

    Object-based classification of grasslands from high resolution satellite image time series using gaussian mean map kernels

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    This paper deals with the classification of grasslands using high resolution satellite image time series. Grasslands considered in this work are semi-natural elements in fragmented landscapes, i.e., they are heterogeneous and small elements. The first contribution of this study is to account for grassland heterogeneity while working at the object level by modeling its pixels distributions by a Gaussian distribution. To measure the similarity between two grasslands, a new kernel is proposed as a second contribution: the a-Gaussian mean kernel. It allows one to weight the influence of the covariance matrix when comparing two Gaussian distributions. This kernel is introduced in support vector machines for the supervised classification of grasslands from southwest France. A dense intra-annual multispectral time series of the Formosat-2 satellite is used for the classification of grasslands’ management practices, while an inter-annual NDVI time series of Formosat-2 is used for old and young grasslands’ discrimination. Results are compared to other existing pixel- and object-based approaches in terms of classification accuracy and processing time. The proposed method is shown to be a good compromise between processing speed and classification accuracy. It can adapt to the classification constraints, and it encompasses several similarity measures known in the literature. It is appropriate for the classification of small and heterogeneous objects such as grasslands

    The influence of spatial and temporal discontinuities of forest habitats on the current presence of flightless saproxylic beetles

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    Flightless saproxylic beetles were selected in order to study the impact of temporal and spatial discontinuity of forests. They were chosen because: (1) they are unable to fly, making them dispersal-limited species, (2) they have a saproxylic diet, which means they are closely linked to the forest, and (3), they have rarely been studied. Forest temporal continuity was expected to be the main factor explaining the presence of these species, modulated by the past and present amount of forest in the surrounding landscape. Twenty-seven forests, distributed into three zones, were sampled in southwestern France. Flightless saproxylic beetles were surveyed using a Winkler extractor and a Berlese funnel. Their presence/absence were modelled using generalised linear mixed models, with zone variable as random effect. Two species showed significant zone effect and were only or more present in the zone with the highest present forest amount in a 0.5 km radius. In the model that converged, the only selected variable was the past amount of forest in the landscape. The size of the forest, the presence of dead wood and the forest temporal continuity were not included in this model. The importance of the amount of forest in the landscape supports the hypothesis that dispersal-limited species are affected by landscape characteristics. This study demonstrates an important link between the presence of Dienerella clathrata and the amount of forest in the past, which led to an indicator species analysis being performed

    Utilisation des sĂ©ries temporelles d’images Sentinel-2 pour la cartographie de l’occupation du sol dans un contexte de modĂ©lisation de la biodiversitĂ©

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    La connaissance de l’occupation du sol actualisĂ©e est une donnĂ©e essentielle pour de nombreuses applications scientifiques et opĂ©rationnelles. À ce titre, il s’agit d’une donnĂ©e permettant de dĂ©river plusieurs variables essentielles de biodiversitĂ©, telles que l’étendue et la fragmentation des Ă©cosystĂšmes ainsi que la structure paysagĂšre, variables fortement reliĂ©es au potentiel de biodiversitĂ© d’un paysage (Skidmore et al., 2015). Elle reprĂ©sente une donnĂ©e d’entrĂ©e essentielle des modĂšles prĂ©dictifs ou de simulation paysagĂšre dĂ©veloppĂ©es en recherche en Ă©cologie du paysage. À l’heure actuelle, il existe plusieurs jeux de donnĂ©es d’occupation du sol de rĂ©fĂ©rence, comme Corine Land Cover (CLC) Ă  l’échelle europĂ©enne ou la BD TOPOÂź de l’IGN Ă  l’échelle nationale française. Ces deux jeux de donnĂ©es permettent de dĂ©crire l’occupation du sol de maniĂšre exhaustive et harmonisĂ©e sur de larges Ă©tendues gĂ©ographiques. Cependant, la faiblesse de CLC rĂ©side dans sa fraĂźcheur temporelle, Ă  savoir que sa diffusion intervient tardivement par rapport Ă  la pĂ©riode temporelle qu’elle dĂ©crit. Si CLC dispose d’une typologie trĂšs dĂ©taillĂ©e, intĂ©grant des notions d’usage du sol, la BD TOPOÂź, si elle dĂ©crit prĂ©cisĂ©ment les Ă©lĂ©ments permanents du paysage, n’identifie pas diffĂ©rentes classes annuelles du paysage telles que les cultures. L’avĂšnement rĂ©cent de la mission spatiale Sentinelle-2 qui fournit de sĂ©ries temporelles d’images satellites, Ă  forte capacitĂ© de revisite (5 jours) et une rĂ©solution spatiale dĂ©camĂ©trique sur l’ensemble de la surface terrestre, ouvre ainsi de nouvelles opportunitĂ©s dans la cartographie de l’occupation du sol actualisĂ©e Ă  grande Ă©chelle. Dans ce sens, le CESBIO avec des contributions de l’UMR Dynafor, dans le cadre du centre d’expertise scientifique « Occupation du Sol » (CES OSO) du PĂŽle ThĂ©matique Surfaces Continentales THEIA a dĂ©veloppĂ© une chaĂźne opĂ©rationnelle de classification supervisĂ©e automatique d’images Sentinelle-2 et Landsat-8 (iota2) produisant une cartographie de l’occupation du sol actualisĂ©e. L’occupation du sol est dĂ©crite grĂące Ă  17 classes, couvrant les grands ensembles paysagers (urbain, agricole et semi-naturel), Ă  une rĂ©solution spatiale de 10 m et une unitĂ© minimale de collecte de 0.01 ha (UMC). La prĂ©cision globale proche de 90% permet son utilisation tant dans des contextes opĂ©rationnels et scientifique d’aide Ă  la dĂ©cision (Inglada et al., 2017). Cette prĂ©sentation dĂ©crira, dans une premiĂšre partie, les caractĂ©ristiques de ce produit cartographique, de sa mĂ©thode de production et de sa qualitĂ© statistique. Dans une seconde partie, la question de l’incertitude spatiale de cette carte d’occupation du sol sera abordĂ©e. Une comparaison avec un jeu de donnĂ©es d’occupation du sol digitalisĂ© manuellement sera prĂ©sentĂ©e au travers d’une modĂ©lisation spatialisĂ©e espĂšce-habitat fondĂ©e sur la surface, l’hĂ©tĂ©rogĂ©nĂ©itĂ© et la connectivitĂ© forestiĂšre d’un paysage agricole pour expliquer la richesse spĂ©cifique de syrphes (ordre des mouches) (Herrault et al., 2016). Les rĂ©sultats tendent Ă  montrer un effet nĂ©gligeable de l’incertitude spatiale sur les performances du modĂšle alors qu’en parallĂšle le recours Ă  la cartographie par tĂ©lĂ©dĂ©tection de l’occupation du sol permet d’envisager une analyse plus systĂ©matique de l’effet de la matrice paysagĂšre dans son ensemble sur la biodiversitĂ©

    Étude du potentiel des donnĂ©es hyperspectrales en vue de dĂ©velopper une mĂ©thode de cartographie automatique du patrimoine arborĂ© en milieu urbain

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    Étude du potentiel des donnĂ©es hyperspectrales en vue de dĂ©velopper une mĂ©thode de cartographie automatique du patrimoine arborĂ© en milieu urbain

    Assessing land cover changes in the French Pyrenees since the 1940s A semi‐automatic GEOBIA approach using aerial photographs

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    International audienceAgro-pastoral landscapes of the Pyrenees are subject to fast spontaneous reforestation. The objective of this work is to assess the spatial patterns of land cover changes during the last 70 years in three study sites of the Pyrenees, and to compare the local dynamics in order to observe and to explain similarities and disparities
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