Statistics of Link Blockage due to Cloud Cover for Free-space Optical Communications using NCDC Surface Weather Observation Data

摘要

Cloud opacity is one of the main atmospheric physical phenomena that can jeopardize the successful completion of an optical link between a spacecraft and a ground station. Hence, the site location chosen for a telescope used for optical communications must rely on knowledge of weather and cloud cover statistics for the geographical area where the telescope itself is located. In this work, the effects of cloud cover on an optical link are statistically described, considering ten observation sites at locations in the southwestern United States, from California to Texas. The data used for the preparation of this work are surface observation data provided by the National Climatic Data Center (NCDC). NCDC provides hourly information on the cloud coverage of an observation site. Using proper algorithms, these data give a statistical description of link blockage over the ten selected observation sites. Statistics averaged over a number of years for each observation site are presented. Cloud coverage statistics for two and three site diversity are also given for a ground network of optical telescopes. Finally, it is shown quantitatively how the use of two or three telescopes can improve the probability of completion of an optical link and how to select the right locations for a ground network of telescopes in the southwestern United States.