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International audience; Because radiation from flames is often the dominant mechanism for wildfire spread, detailed information on flame properties is required. The proposed procedure combines a spectrally resolved radiation model for simulating the line-of-sight infrared emission intensity and spectroscopy data and uses a genetic algorithm (GA) to determine a set of flame properties, allowing optimal agreement between model and outdoor experiments. GA calibration and sensitivity analysis were conducted using well-defined reference flames. The combined GA/radiation model was used with emission data to estimate the effective properties of flames from the combustion of woody fuel beds from 0.5 to 4 m in thickness. Experimental results show that the contribution of soot particles to flame emission increases with flame thickness. The GA was found to be robust and efficient in providing relevant flame properties from line-of-sight intensities on the infrared spectrum of radiation.

This paper presents the latest developments and validation results of a hybrid model which combines a broad-scale stochastic small-world network model with a macroscopic deterministic approach, to simulate the effects of large fires burning in heterogeneous landscapes. In the extended version of the model, vegetation is depicted as an amorphous network of combustible cells, and both radiation and convection from the flaming zone are considered in the preheating process of unburned cells. Examples are given to illustrate small-world effects and fire behavior near the percolation threshold. The model is applied to a Mediterranean fire that occurred in Corsica in 2009 showing a good agreement in terms of rate of spread, and area and shape of the burn. A study, based on a fractional factorial plan, is conducted to evaluate the influence of variations of model parameters on fire propagation.

International audience; As an alternative to the classical deterministic methods, a Monte Carlo method is proposed for the estimation of the radiant heat flux from wildland fires, and thus of fire-safe distances. The solid flame model is used, in which the flame is regarded as a uniformly-radiating surface with a simple geometry. Case studies are presented, ranging from the relatively simple case of planar or cylindrical flames to the case of the more complex geometries of irregular flame fronts where the strategy consists in approximating the front as a collection of individual solid flames. Model results are in good agreement with available data. An attempt is made to estimate the radiant heat flux ahead of a fire front spreading on a heterogeneous landscape. Finally the model is applied to determine the defensible space around a structure in which combustible vegetation has been totally cleared in the aim of reducing the wildfire threat to homes. (C) 2010 Elsevier Masson SAS. All rights reserved.

International audience; A series of outdoor experiments were conducted in a fire tunnel to measure the emission of infrared radiation from wildland flames, using a FTIR spectrometer combined with a multispectral camera. Flames of different sizes were produced by the combustion of vegetation sets close to wildland fuel beds, using wood shavings and kermes oak shrubs as fuels. The nongray radiation of the gas-soot mixture was clearly observed from the infrared emitted intensities. It was found that the flame resulting from the combustion of the 0.50 m long fuel bed, with a near-zero soot emission, may be considered as optically thin and that the increase in bed length, from 1 to 4 m, led to an increase in flame thickness, and therefore, in flame emission with contributions from both soot and gases. A further analysis of the emission was conducted in order to evaluate effective flame properties (i.e., emissivity, extinction coefficient, and temperature). The observation of emission spectra suggests thermal nonequilibrium between soot particles and gas species that can be attributed to the presence of relatively cold soot and hot gases within the flame.

This paper presents the development and validation results of a weighted small-world network model designed to simulate fire patterns in real heterogeneous landscapes. Fire spread is simulated on a gridded landscape, a mosaic in which each cell represents an area of the land surface. In this model, the interaction between burning and non-burning cells (here, due to flame radiation) may extend well beyond nearest neighbors, and depends on local conditions of wind, topography, and vegetation. An approach based on the coupling of the solid flame model with the Monte Carlo method is used to predict the radiative heat flux from the flame generated by the burning of each combustible cell to its neighbors. The weighting procedure takes into account latency (a combustible cell will only ignite when it has accumulated enough energy along time) and flaming persistence of burning cells. The model is applied to very different fire scenarios: a historical Mediterranean fire that occurred in southeastern France in 2005 and experimental fires conducted in arid savanna fuels in South Africa in 1992. Model results are found to be in agreement with real fire patterns, in terms both of rate of spread, and of the area and shape of the burn. This work also shows that the fractal properties of fire patterns predicted by the model are similar to those observed from satellite images of three other Mediterranean fire scars.

International audience; Excavated from 2003 to 2011, the site of Beg ar Loued in the southern part of Molène Island has yielded the remains of two dry stone houses superimposed and occupied between 2150 and 1750 cal BC. At this time, the Molène Archipelago was in a similar form as today, except the foreshores, which were much larger. The site was then a hundred meters from the shoreline. The study of the site allows a more comprehensive understanding of the way of life of this island society. They used to farm and breed livestock, supplemented by fishing on the foreshore, collecting limpets and to a lesser extent hunting migratory birds. The material culture shows that this group used local resources: clay, sea pebbles and outcrops. This picture of a self-sufficient society must be qualified. Indeed, the architecture of buildings, the ceramic forms, the lithic technology and the metalworking are evidence that this society was linked with what was happening on the mainland. That raises question of seafaring and the nature of the links between this island society and the continent.; Fouillé de 2003 à 2011, le site de Beg ar Loued au sud de l’île de Molène a livré les vestiges de deux maisons en pierres sèches superposées et occupées de 2150 à 1750 cal. BC. À cette période, le plateau Molénais, déjà insulaire depuis le Néolithique ancien, se présentait dans une forme assez proche de l’actuel, exception faite des estrans qui étaient beaucoup plus vastes. Le site se trouvait alors à une centaine de mètres du trait de côte. L’étude du site a permis de mieux comprendre le mode de vie de cette com-munauté insulaire. Celle-ci pratiquait l’agriculture et l’élevage, complétés par la pêche sur estran, la collecte des patelles et, dans une moindre mesure, la chasse aux oiseaux migrateurs. La culture matérielle montre que ce groupe exploitait les ressources locales : argile, cordons de galets et affleurements rocheux. Ce tableau d’une société autarcique se doit pourtant d’être nuancé, car l’architecture des bâtiments, les formes céramiques, la technologie lithique et la métallurgie sont autant d’indices montrant que cette société n’était pas à l’écart des circuits d’échange et qu’elle était en phase avec les changements et les innovations culturels identifiés sur le proche conti-nent. Dès lors, se pose la question de la navigation et de la nature des liens qu’entretenait cette communauté insulaire avec le continent.