Surface roughness of ice crystals is a morphological parameter important to the scattering characteristics of these particles. The intent of this study is to quantify the effect of surface roughness on the retrieval of the optical and microphysical properties of cirrus clouds from satellite observations. We present two ray-tracing algorithms, a rigorous algorithm and an approximate algorithm with a simplified treatment of surface roughness, for calculating the single-scattering properties of randomly oriented hexagonal ice crystals with size parameters in the geometric optics regime. It is shown that the simplified scheme can account for most the effects of surface roughness on particle single-scattering properties without incurring substantial demand on computational resources, and thus provides an efficient way to compute the single-scattering properties of roughened particles. The simplified ray-tracing technique is employed to compute the single-scattering properties of hexagonal columns at wavelengths 0.86 and 2.13 ?m. Look-up tables built for the correlation between the bi-directional reflectances at wavelengths 0.86 and 2.13 ?m with different roughness conditions are used to retrieve ice cloud optical thickness and effective particle size over oceans. In general, the dominant effect of surface roughness on cloud property retrievals is to decrease the retrieved optical thickness and to increase the retrieved effective particle size in comparison with their counterparts in the case of smooth ice particles.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0319 Cloud optics;
- 0321 Cloud/radiation interaction;
- 0360 Radiation: transmission and scattering