38 research outputs found
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A change detection approach to flood mapping in urban areas using TerraSAR-X
Very high-resolution Synthetic Aperture Radar sensors represent an alternative to aerial photography for delineating floods in built-up environments where flood risk is highest. However, even with currently available SAR image resolutions of 3 m and higher, signal returns from man-made structures hamper the accurate mapping of flooded areas. Enhanced image processing algorithms and a better exploitation of image archives are required to facilitate the use of microwave remote sensing data for monitoring flood dynamics in urban areas. In this study a hybrid methodology combining radiometric thresholding, region growing and change detection is introduced as an approach enabling the automated, objective and reliable flood extent extraction from very high-resolution urban SAR images. The method is based on the calibration of a statistical distribution of “open water” backscatter values inferred from SAR images of floods. SAR images acquired during dry conditions enable the identification of areas i) that are not “visible” to the sensor (i.e. regions affected by ‘layover’ and ‘shadow’) and ii) that systematically behave as specular reflectors (e.g. smooth tarmac, permanent water bodies). Change detection with respect to a pre- or post flood reference image thereby reduces over-detection of inundated areas. A case study of the July 2007 Severn River flood (UK) observed by the very high-resolution SAR sensor on board TerraSAR-X as well as airborne photography highlights advantages and limitations of the proposed method. We conclude that even though the fully automated SAR-based flood mapping technique overcomes some limitations of previous methods, further technological and methodological improvements are necessary for SAR-based flood detection in urban areas to match the flood mapping capability of high quality aerial photography
SA 06. Integrated control of Strongylosis of small ruminants in the humid tropics: a component of animal production system that required a pluridiciplinary approach
Internal parasitosis, mainly due to nematodes is well known to induce important economic losses in small ruminant production in tropical areas. Strongyloses are the more frequent diseases and became one of the main constraints in small ruminant production in the Caribbean. Research works are generally conducted with a disciplinary approach in Latin America: veterinarians focus on parasitology whereas animal production scientists focus on breeding systems. However, there are now sufficient data that emphasized the need for a global approach to set up efficient plans of integrated control for animal production in sustainable systems. This paper reviews the main research results obtained in the F.W.I. on these parasitizes and describes the pluridiciplinary research that is developed locally in the Animal Production Research Unit (APRU) to improved small ruminant grazing systems taking into account the inevitable gastrointestinal (GI) nematodes, as a component of the production systems
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Assimilation of probabilistic flood maps from SAR data into a coupled hydrologic–hydraulic forecasting model: a proof of concept
Coupled hydrologic and hydraulic models represent
powerful tools for simulating streamflow and water levels
along the riverbed and in the floodplain. However, input
data, model parameters, initial conditions, and model structure
represent sources of uncertainty that affect the reliability
and accuracy of flood forecasts. Assimilation of satellitebased
synthetic aperture radar (SAR) observations into a
flood forecasting model is generally used to reduce such uncertainties.
In this context, we have evaluated how sequential
assimilation of flood extent derived from SAR data can help
improve flood forecasts. In particular, we carried out twin
experiments based on a synthetically generated dataset with
controlled uncertainty. To this end, two assimilation methods
are explored and compared: the sequential importance sampling
method (standard method) and its enhanced method
where a tempering coefficient is used to inflate the posterior
probability (adapted method) and reduce degeneracy. The experimental
results show that the assimilation of SAR probabilistic
flood maps significantly improves the predictions of
streamflow and water elevation, thereby confirming the effectiveness
of the data assimilation framework. In addition,
the assimilation method significantly reduces the spatially
averaged root mean square error of water levels with respect
to the case without assimilation. The critical success index of
predicted flood extent maps is significantly increased by the
assimilation. While the standard method proves to be more
accurate in estimating the water levels and streamflow at the
assimilation time step, the adapted method enables a more
persistent improvement of the forecasts. However, although
the use of a tempering coefficient reduces the degeneracy
problem, the accuracy of model simulation is lower than that
of the standard method at the assimilation time step
A global network for operational flood risk reduction
Every year riverine flooding affects millions of people in developing countries, due to the large population exposure in the floodplains and the lack of adequate flood protection measures. Preparedness and monitoring are effective ways to reduce flood risk. State-of-the-art technologies relying on satellite remote sensing as well as numerical hydrological and weather predictions can detect and monitor severe flood events at a global scale. This paper describes the emerging role of the Global Flood Partnership (GFP), a global network of scientists, users, private and public organizations active in global flood risk management. Currently, a number of GFP member institutes regularly share results from their experimental products, developed to predict and monitor where and when flooding is taking place in near real-time. GFP flood products have already been used on several occasions by national environmental agencies and humanitarian organizations to support emergency operations and to reduce the overall socio-economic impacts of disasters. This paper describes a range of global flood products developed by GFP partners, and how these provide complementary information to support and improve current global flood risk management for large scale catastrophes. We also discuss existing challenges and ways forward to turn current experimental products into an integrated flood risk management platform to improve rapid access to flood information and increase resilience to flood events at global scale
A Review of Flood-Related Storage and Remobilization of Heavy Metal Pollutants in River Systems
L'élevage en Guyane. Bilan des travaux réalisés sur les espèces domestiques et sur deux espèces sauvages autochtones
International audienc
Reproductive biology of the neotropical armoured catfish Hoplosternum littorale (Siluriformes, Callichthyidae) : a synthesis stressing the role of the floating bubble nest (tropical swamps, hypoxic environment, foam nest, multiple spawning, parental care)
Simulation du comportement thermique en régime permanent d'un moteur asynchrone à refroidissement extérieur. Etude par éléments finis
The steady state thermal modelling of an 4 kW asynchronous motor is realized. A design has been made thanks to the Flux2D finite element magnetic calculus software converted into a resolution tool of the heat equation. This last is used to simulate the heat flux in fluid and solid areas. A 3D study is effected thanks to two 2D studies. The first concerns a radial view (perpendicular to the mechanical axis) whereas the second is effected for an axial view (parallel to the mechanical axis). Thermal conductivities of the materials and thermal contact resistances of the motor are determined through two different tests creating different overheatings. The first is made with a sinewave supply and pre-determine the thermophysical parameters. The second effected with direct current supplies at the rotor and the stator is used to validate these last parameters.
On réalise l'étude du comportement thermique en régime permanent d'un moteur asynchrone de 4 kW. Le logiciel de calculs magnétiques par éléments finis flux2D est converti en un outil de résolution de l'équation de la chaleur. Cette dernière équation sert à simuler les transferts thermiques tant dans les domaines fluides que solides. Une pseudo-étude tridimensionnelle est réalisée par le biais de deux études bidimensionnelles : la première effectuée suivant un plan radial (plan perpendiculaire à l'axe du moteur) et la seconde suivant un plan axial (plan parallèle à l'axe). Les conductivités des matériaux et des résistances thermiques de contact composant le moteur sont déterminées à l'aide de deux types d'essais qui induisent des échauffements différents. Le premier est réalisé avec une alimentation sinusoïdale et sert à prédéterminer les paramètres thermophysiques. Le second est effectué avec des alimentations à courant continu tant au stator qu'au rotor et a pour rôle la validation de ces paramètres
From isolates to a synthetic laboratory population : maintenance of variability in the nematode Haemonchus contortus
Haemonchus contortus isolates were collected from goats of five locations with different climatic characteristics in Guadeloupe archipelago. They were investigated for morphology, morphometrics and allozyme diversity after passage in immunosuppressed lambs using long acting corticoids. The basic aim of the work was to construct a synthetic strain in laboratory conditions which was representative of the isolates. The isolates were only slightly different although climatic conditions were very different. The resemblance of isolates might be due to the practice of goat exchanges between farms or to their insular origin. However the isolate from a smaller island (Les Saintes) was different (mostly on morphometrics) from all the others originating from Guadeloupe main island. The first assemblage in laboratory resulting from the installation from a mixture of the five isolates was not very representative, whereas the next generation (synthetic strain) resembled all the isolates as shown from allozyme study. Female fecundity and length in established synthetic strain were lower than that recorded in isolates, indicating a decrease in fitness, possibly due to the stability of experimental environment. The representativity of the synthetic strain was good but the strain could still evoluate on further passages and should be evaluated on a large number of generations maintained in laboratory
From isolates to a synthetic laboratory population : maintenance of variability in the nematode
Haemonchus contortus isolates were collected from goats of five locations with different climatic characteristics in Guadeloupe archipelago. They were investigated for morphology, morphometrics and allozyme diversity after passage in immunosuppressed lambs using long acting corticoids. The basic aim of the work was to construct a synthetic strain in laboratory conditions which was representative of the isolates. The isolates were only slightly different although climatic conditions were very different. The resemblance of isolates might be due to the practice of goat exchanges between farms or to their insular origin. However the isolate from a smaller island (Les Saintes) was different (mostly on morphometrics) from all the others originating from Guadeloupe main island. The first assemblage in laboratory resulting from the installation from a mixture of the five isolates was not very representative, whereas the next generation (synthetic strain) resembled all the isolates as shown from allozyme study. Female fecundity and length in established synthetic strain were lower than that recorded in isolates, indicating a decrease in fitness, possibly due to the stability of experimental environment. The representativity of the synthetic strain was good but the strain could still evoluate on further passages and should be evaluated on a large number of generations maintained in laboratory