Modeling of light scattering in cirrus clouds with inhomogeneous hexagonalmonocrystals. Comparison with in-situ nd ADEOS-POLDER measurements

An Inhhomogeneous Hexagonal Monocrystal (IHM) model is used to simulate lig ht scattering by randomly oriented hexagonal ice crystals containing air bu bbles. This model based on a combination of ray-tracing, Mie theory and Mon te-Carlo techniques, allows to retrieve the scattering-phase function. In-s itu measurements of the light scattering:diagram in natural cirrus clouds w ith an airborne nephelometer have been performed. The results given by the IHM model have been favorably adjusted with these measurements.: This agree ment provides an opportunity to use this model in order to analyze ADEOS-PO LDER reflectance measurements over cirrus clouds. POLDER uses an original c oncept to measure, for a given scene, total and polarized reflectances unde r several viewing directions. A first analysis of cirrus cloud spherical al bedoes for the 10th November 1996 shows a rather good agreement between mea surements and calculations.