Etude des propriétés optiques et radiatives des cirrus par télédetection active : apport des observations polarisées

Abstract : Clouds remain a major source of uncertainty when studying the Earth climate. Among them, cirrus clouds are crucial due to their high greenhouse and albedo effect. Unfortunately, their study is difficult due their high altitude and complex composition. During the last twenty years, several field campaigns have shown the high variability of their microphysical properties : the size, shape and orientation of crystals inside the cloud. This lack of knowledge leads to arbitrary assumptions in their modelisation, meaning incoherent results in large-scale climatic simulations. New techniques must be developed, benefiting from the unique capabilities of remote sensing instruments. This thesis studies the potential contribution of spatial measurements for the characterization of ice clouds properties, in order to prepare the Aqua-Train mission, a satellite constellation dedicated to atmospheric studies. Scattering phenomenon in ice crystals have been modelled, taking into account several of their properties and leading to the retrieval of cirrus microphysical parameters through the study of measured light polarization state. Both active and passive remote sensing measurements were used. These techniques have been actually applied to ground-based measurements, and their potential application to space measurements has been evaluated. Bind together into an homogenous framework, they led to the retrieval of all cirrus microphysical properties : crystal orientation and maximum deviation angle from polarized measurements (scanning lidar, radiometer) ; crystal shape ratio from polarization lidar ; crystal size from a multi-instruments algorithm. The retrieval of such parameters on a global scale should lead to a better understanding of cirrus radiative properties, and to a better evaluation of their importance in the context of the Earth radiation budget.
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Submitted on : Thursday, July 8, 2004 - 7:03:48 PM
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  • HAL Id : tel-00006430, version 1

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Vincent Noel. Etude des propriétés optiques et radiatives des cirrus par télédetection active : apport des observations polarisées. Océan, Atmosphère. Université Paris-Diderot - Paris VII, 2002. Français. 〈tel-00006430〉

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