Scattering matrices of ice crystals

The present report describes the results of an eight months working visit of M.H. at KNMI. The goal of this visit was the implementation of cirrus clouds in the DAK radiative transfer model (De Haan et al., 1987; Stammes, 1994)). With this addition the DAK model can be used for the interpretation of satellite measurements of cirrus clouds.
The DAK radiative transfer model requires scattering matrices of atmospheric constituents which influence the radiation field in the atmosphere. The scattering matrices of ice crystals are calculated with help of a raytracing code using the georetric optics approximation, which is valid for particles considerably larger than the wavelength of the scattered radiation. An existing raytracing code for hexagonal columnar and platelike ice crystals (Hess and Wigner, 1994) is extended to calculate the complete 4 x 4 scattering matrix containing the full polarisation information. It is also extended to allow calculations for spherical particles and for non-ideal hexagonal crystals. Scattering by non-ideal ice crystals is modelled by means of statistical variation of ray paths during the raytracing in regular hexagonal particles. A first application to radiative transfer calculations of cirrus clouds is shown.