Determination of ice cloud models using MISR measurements

A number of ice cloud models are examined using multiangle measurements of reflectance obtained from the Multi-angle Imaging SpectroRadiometer (MISR) instrument. The single-scattering properties of ice crystals are computed by an Improved Geometric Optics Method (IGOM) based on retracing technique. Ice crystal habits, including surface smooth and rough, homogeneous and inhomogeneous ice crystals and aggregates of hexagonal ice crystals are considered in light scattering computations. Our preliminary results show that ice crystal surface roughness and inhomogeneity have a smoothing effect to the single-scattering phase functions. The bulk optical properties are obtained from averaging the single-scattering properties of ice crystals over several particle size and habit distributions. Spherical albedos and optical thicknesses of ice clouds are derived at nine different viewing directions and as functions of scattering angles. They are used to test the validity of ice cloud models associated with morphological parameters of ice crystals and particle size and habit distributions. The best ice cloud model has the minimum differences between spherical albedos from different viewing angles. This ice cloud model is used to retrieve ice cloud microphysical and optical properties using MODIS-Terra measurements. The results are compared with the operational MODIS retrievals. Moreover, the error of ice cloud optical thickness retrievals from using MISR measurements at different viewing angles is studied.