A Monte Carlo code based on the geometric optics approach which applies to spheroids and polyhedral particles composed of one or more materials has been developed. The phase functions of hexagonal solid columns have been integrated with a log-normal particle size distribution and used as an input to the radiation transfer program based on the discrete ordinates method ('rstar' program of Center for Climate System Research, University of Tokyo) to calculate expected measured radiances from space. It was found that a difference of calculated reflected radiances with a case of spherical particles is large. This result indicates that one can not apply the Mie theory, which is valid for retrievals only in the case of spherical particles, to calculate radiative properties of cirrus clouds.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.