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Theses

Caractérisation de la neige, du névé et de la glace par traitement d'images.

Abstract : It is now recognized that human activities , by the extent they have achieved since the industrial era, are likely to alter the Earth's climate (IPCC, 1996). Paleo climate and the climate change models show that the polar caps are particularly sensitive to global climate change. They are more likely to play an important role but unknown on the sea level. The positive term of mass balance of polar ice sheets is the accumulation of snow, whereas the negative term is formed by the flow of ice into the oceans . The size of the polar ice caps and their hostile environment limit the amount of available field data . Only satellite remote sensing is able to provide information on geographical scales as large as Antarctica or the Arctic and allows regular monitoring over time. But to be easily interpreted, in order to deduce the snowpack characteristics observed from space (size, shape of grains, surface roughness ... ), satellite data should be validated and inverted using simplified parameters . Prior to the establishment of these relations, it is necessary to develop a snow reflectance model ( thesis C. Leroux 1996) taking into account the physical and optical characteristics of the snow, and a microwave emissivity model (thesis Surdyck S. 1993) that provide volume information on the morphology of the snowpack. The snowpack is characterized by several physical parameters that depend on the depth: temperature, density , size and shape of grains mainly . It is therefore essential to establish a robust and simple parameterization of the size and shape of snow grains from their observation. Image processing allows to establish these relationships and allows automatic processing of a large number of data independent of the observer. Another glaciological problem of firn is the interpretation of data obtained from the analysis of trapped air bubbles in the gas . This study implies, in particular , the dating of the ice in the firn at the close off, is necessary to determine the age of gas with respect to the ice age. Dating gases contained in the bubbles ice cores is done from the ice age , therefore , it requires knowledge of the age difference between the gas and ice during the close off. During the close off, the calculation of the ice age requires a densification model and the age of the gas requires a transport model(thesis Amand L. 1997). Both models will be fully exploited only if the density at the close off is known with precision, we develop a third physical model of the close off in polar firn . The cores made in the central regions of Antarctica and Greenland allows to obtain experimental data essential to characterize the polar firn . Only the automatic image processing from these data is able to provide the structure parameters introduced in the models of densification, of close off, and of gas diffusion . Another aspect studied at the Laboratory of Glaciology is the increase in the average size of ice crystals ( or grains) with depth or ice age. The crystal growth was described in the glaciological literature ( Gow 1969, 1971 and 1975, Narita et al 1978 . Duval and Lorius 1980 A11ey et al 1982 . Duval 1985 Alley and Bentley 1988). Manual analysis of thin sections of ice to determine these coarsening laws will now be performed automatically by 2D image processing. The increase in the average size is only one parameter changes of the ice microstructure related to the normal grain growth . The use of image processing applied to the study of such microstructures will allow the observation and analysis of these microstructures in terms of evolution and size distributions and in terms of changes in the topology of the grains.
Mots-clés : Image Neige Névé Glace
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Submitted on : Tuesday, January 14, 2014 - 1:27:15 PM
Last modification on : Tuesday, March 17, 2020 - 2:50:40 AM
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Michel Gay. Caractérisation de la neige, du névé et de la glace par traitement d'images.. Géophysique [physics.geo-ph]. Université de Grenoble, 1999. Français. ⟨tel-00930144⟩

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