Link Availability Model for Optical Communication through Clouds

摘要

The effects of clouds on optical down-links (satellite to ground) have been recognized by a variety of authors. However, the typical approach has been simply to explore the probability of a "cloud-free line of sight." This somewhat ambiguous criterion does not acknowledge that a communication link, albeit at a degraded data rate, could still be established in the presence of clouds of certain optical thicknesses. Moreover, it's not obvious what "cloud-free" means. Is there some implied threshold below which the path is considered to be free of clouds? To realistically model the effects of clouds on the performance of an optical communication system, we make use of existing databases that contain cloud statistics parameterized on optical density. In conjunction with these statistics, we use a radiation transport model parameterized on optical thickness that describes the spatio-temporal spreading effects of multiple scatter. Scatter characteristics (scatter and extinction cross-sections, asymmetry parameters) used in this model are determined from particle size distributions by Mie theory. Together, these databases and this model allow derivation of link availability probabilities. Results are presented in terms of geographic probability maps of communication at or above prescribed bandwidths.