Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
BACKGROUND: Sampling design is a key issue when establishing species inventories and characterizing habitats within highly heterogeneous landscapes. Sampling efforts in such environments may be constrained and many field studies only rely on subjective and/or qualitative approaches to design collection strategy. The region of Cacao, in French Guiana, provides an excellent study site to understand the presence and abundance of Anopheles mosquitoes, their species dynamics and the transmission risk of malaria across various environments. We propose an objective methodology to define a stratified sampling design. Following thorough environmental characterization, a factorial analysis of mixed groups allows the data to be reduced and non-collinear principal components to be identified while balancing the influences of the different environmental factors. Such components defined new variables which could then be used in a robust k-means clustering procedure. Then, we identified five clusters that corresponded to our sampling strata and selected sampling sites in each stratum. RESULTS: We validated our method by comparing the species overlap of entomological collections from selected sites and the environmental similarities of the same sites. The Morisita index was significantly correlated (Pearson linear correlation) with environmental similarity based on i) the balanced environmental variable groups considered jointly (p = 0.001) and ii) land cover/use (p-value<0.001). The Jaccard index was significantly correlated with land cover/use-based environmental similarity (p-value = 0.001). CONCLUSIONS: The results validate our sampling approach. Land cover/use maps (based on high spatial resolution satellite images) were shown to be particularly useful when studying the presence, density and diversity of Anopheles mosquitoes at local scales and in very heterogeneous landscapes.
BMC Ecology

pasteur-00914104
https://hal-riip.archives-ouvertes.fr/pasteur-00914104
https://hal-riip.archives-ouvertes.fr/pasteur-00914104/document
DOI : 10.1186/1472-6785-13-45
PUBMED : 24289184

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
ABSTRACT: BACKGROUND: Climate change poses unprecedented challenges, ranging from global and local policy challenges to personal and social action. Heat-related deaths are largely preventable, but interventions for the most vulnerable populations need improvement. Therefore, the prior identification of high risk areas at the community level is required to better inform planning and prevention. We aimed to demonstrate a simple and flexible conceptual framework relying upon satellite thermal data and other digital data with the goal of easily reproducing this framework in a variety of urban configurations. RESULTS: The study area encompasses Rennes, a medium-sized French city. A Landsat ETM + image (60 m resolution) acquired during a localized heatwave (June 2001) was used to estimate land surface temperature (LST) and derive a hazard index. A land-use regression model was performed to predict the LST. Vulnerability was assessed through census data describing four dimensions (socio-economic status, extreme age, population density and building obsolescence). Then, hazard and vulnerability indices were combined to deliver a heatwave health risk index. The LST patterns were quite heterogeneous, reflecting the land cover mosaic inside the city boundary, with hotspots of elevated temperature mainly observed in the city center. A spatial error regression model was highly predictive of the spatial variation in the LST (R2 = 0.87) and was parsimonious. Three land cover descriptors (NDVI, vegetation and water fractions) were negatively linked with the LST. A sensitivity analysis (based on an image acquired on July 2000) yielded similar results. Southern areas exhibited the most vulnerability, although some pockets of higher vulnerability were observed northeast and west of the city. The heatwave health risk map showed evidence of infra-city spatial clustering, with the highest risks observed in a north--south central band. Another sensitivity analysis gave a very high correlation between 2000 and 2001 risk indices (r = 0.98, p < 10-12). CONCLUSIONS: Building on previous work, we developed a reproducible method that can provide guidance for local planners in developing more efficient climate impact adaptations. We recommend, however, using the health risk index together with hazard and vulnerability indices to implement tailored programs because exposure to heat and vulnerability do not require the same prevention strategies.
ISSN: 1476-072X

inserm-00762303
http://www.hal.inserm.fr/inserm-00762303
http://www.hal.inserm.fr/inserm-00762303/document
http://www.hal.inserm.fr/inserm-00762303/file/1476-072X-11-38.pdf
DOI : 10.1186/1476-072X-11-38

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

Éditeur(s) : Université de Bretagne Occidentale
Résumé : Several small pelagic fish species contribute remarkably to world catch. Their populations are, however, characterized by large biomass fluctuations strongly affecting fisheries. The fishing gears and methods used to capture small pelagics have evolved to exploit the highly developed shoaling behavior of these species. Hence, faced to modern fishing this gregarious behavior becomes a disadvantage for fish. Fish behavior may be affected by environmental conditions and by fishing, at the same time that behavior impacts fishing. In this study, we seek to characterize the aggregative systems of small pelagic fishes inhabiting the Bay of Biscay by analyzing "acoustic images", defined as the group of echoes (planktonic layers, shoals, isolated targets) detected on a transect section of a given length. We analyzed the species composition, the spatial distribution and the evolution over time of acoustic images. We also studied the hydrological conditions of the bay, as well as the small pelagics French fishery in order to look for correlations between hydrology, commercial catch and fish aggregation patterns observed by acoustics. We observed the same species or group of species forming different types of aggregation according to habitat. Conversely, the same type of aggregation, associated with a particular habitat, can be produced by different species. The most notorious change observed during the studied period relates to small clupeoids aggregations in the vicinity of the Gironde estuary, whose structure evolved toward a greater fragmentation of shoals (a large number of small size detections) since 2000. Concerning commercial catches, pelagic trawlers fishing in pairs mainly seek for anchovy in the coastal areas, single pelagic trawlers capture mackerel and horse mackerel in deeper waters while purse seiners target mostly sardine near their fishing ports. Because of the coarse spatial resolution of commercial fishing data and the effect of the application of an international fisheries agreement limiting the fishing activity of French pelagic trawlers during spring, only small correlations between captures and types of aggregation were observed.
La participation des petits poissons pélagiques dans les captures est remarquable. Leurs populations sont cependant caractérisées par des importantes fluctuations de biomasse, impactant fortement les pêcheries. Les méthodes et appareils de pêche utilisés pour capturer ces espèces ont évolué dans le sens d'exploiter le comportement grégaire très développé des petits pélagiques. Cette tendance à former de bancs devient alors désavantageuse pour le poisson face à la pêche moderne. Les conditions environnementales et la pêche peuvent affecter le comportement du poisson, en même temps que ce dernier est susceptible d'affecter l'activité halieutique. Le but de cette étude est de caractériser les systèmes agrégatifs des petits poissons pélagiques dans le golfe de Gascogne en étudiant des « images acoustiques », définies comme l'ensemble des échos (couches planctoniques, bancs, cibles isolées) détectés sur une section de radiale de longueur donnée. Nous analysons leur composition en espèces ainsi que leur distribution spatiale et leur évolution au cours du temps. Nous étudions aussi les conditions hydrologiques du golfe, ainsi que la pêcherie française de ces espèces afin de chercher des corrélations entre l'hydrologie, la capture commerciale et les types d'agrégations observés par acoustique. Nous avons observé qu'une espèce est capable de former des agrégations différentes en fonction de l'habitat, et inversement, le même type d'agrégation, associé à un habitat particulier, peut être produit par des espèces différentes. Le changement observé le plus évident concerne les agrégations de petits clupéiformes, dont la structure a évolué vers une plus grande fragmentation des détections (des petits bancs plus nombreux) depuis 2000. Par rapport à la pêche des professionnels, les chalutiers pélagiques en boeufs recherchent en priorité l'anchois dans la zone côtière, les pélagiques simples capturent le chinchard et le maquereau au large et les senneurs recherchent principalement la sardine à proximité des ports de pêche. À cause de la résolution spatiale trop sommaire des données de pêche et l'effet de l'application des accords internationaux limitant l'activité des chalutiers pélagiques au printemps, nous n'avons observé que peu des corrélations entre les captures et les types d'agrégation établis à partir de données issues des campagnes scientifiques.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2008/these-6083.pdf
http://archimer.ifremer.fr/doc/00000/6083/

Éditeur(s) : HAL CCSD
Résumé : International audience
In this paper, we use a multifractal approach based on the computation of two spectrums for image analysis and texture segmentation problems. The two spectrums are the Legendre Spectrum, determined by classical methods, and the Large Deviation Spectrum, determined by kernel density estimation. We propose a way for the fusion of these two spectrums to improve textured image segmentation results. An unsupervised k-means is used as clustering approach for the texture classification. The algorithm is applied on mosaic image built using IKONOS images and various natural textures from the Brodatz album. The segmentation obtained with our approach gives better results than the application of each spectrum separately.
CIARP Proceedings
Cancun, Mexico

hal-00602268
https://hal.archives-ouvertes.fr/hal-00602268

Éditeur(s) : HAL CCSD
Résumé : International audience
The « METYSS » cruise was carried out in June 2009 onboard the R/V « Téthys II » along the eastern Sardinian and south-eastern Corsican margins, western Tyrrhenian Sea, in order to better constrain the potential links between deformation related to either crustal tectonics or salt tectonics and sediment accumulation, especially during the Messinian and Plio-Quaternary times. We acquired 15 high-resolution seismic reflection profiles (about 1200 km in cumulative length) along the south-eastern Corsican margin, immediately north of the Bonifacio Strait and along the upper and middle parts of the eastern Sardinian margin, from the continental slope to the Cornaglia Terrace. The Tyrrhenian Sea is considered as a Neogene back-arc basin that opened during continental rifting and oceanic spreading related to the eastward migration of the Apennine subduction system from Tortonian to Pliocene times (Jolivet et al., 2006). Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times and therefore the series of that age should be considered as syn-rift sediments (Sartori et al., 2004). The « METYSS » seismic profiles clearly illustrate that this part of the Tyrrhenian was highly segmented during the rifting stage by N-S trending normal faults delineating ridges (e.g., Baronie Ridge) and basins (e.g., Sardinian Basin and Cornaglia Terrace), as previously described for example by Thommeret (1999) and Sartori et al. (2004). The Messinian sedimentary units and especially the « Upper Unit » (UU, Lofi et al., this congress, corresponding to the « Upper Evaporites » in the previous literature) are, without any doubt, of syn-rift age, as they display a fan-shaped stratal geometry. The Mobile Unit (MU, Lofi et al., this congress), i.e. the Messinian halite, is clearly imaged in the study area and its spatial repartition can be outlined. The highly-variable thickness of the confined salt basins could be due to the initial basin geometry (i.e. before the Messinian salinity Crisis) or to the syn-rift character of the deposition. Southeastward of the study area, in the vicinity of the Cornaglia Seamount, salt tectonics appears surprisingly vigorous. More surprisingly, several normal faults seem to have remained active in recent times, if not even at present time. Fault slip has been recorded by bathymetric scarps and associated footwall debris flows interfingered within the Plio-Quaternary sequence, even though the eastern Sardinian margin is usually considered to be passive now. Moreover, some amount of tectonic inversion is visible on some normal faults that show contractional or transpressional components of late slip. In addition, this “post-rift” deformation can be illustrated within the Plio-Quaternary sequence by a regional unconformity. Consequently, numerous mass-transport deposits and channel-levees systems observed in the Plio-Quaternary cover could be partly controlled by tectonic activity. These very preliminary results require further investigations in order to better decipher the role of crustal tectonics and salt tectonics, salt-related structures being very efficient markers to discriminate between the respective contribution of gravity-driven, salt tectonics and deep-seated, crustal tectonics (Gaullier et al., 2010). Finally, we aim to precisely determine the relative vertical movements (tilting, subsidence, magmatism. . . ) and geodynamical history of the different segments of the area since 6 Ma.
Geophysical Research Abstracts
Vienne, Austria

hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828
https://hal-brgm.archives-ouvertes.fr/hal-00537828/document
https://hal-brgm.archives-ouvertes.fr/hal-00537828/file/EGU2010-15469_ref6821.pdf