Remote sounding of cirrus mean effective particle size from AVHRR radiances

For the present investigation a new method for the calculation of the single scattering and absorption properties of hexagonal ice crystals called the Discretized Mie Formalism (DMF) is used together with a radiative transfer model in order to determine the influence of particle size and shape on the brightness temperature difference (BTD) between the two NOAA AVHRR infrared window channels 4 and 5. Comparing the results to those of optically equivalent spheres it is shown that particle shape has an influence on the observed BTD which is decreasing with increasing particle size.