The mitigation of Atmospheric Impacts on Free Space Optical Communications

Clouds are key driver in the performance of free space optical communication (FSOC) systems. Clouds are composed of liquid water and/or ice crystals and depending on the physical thickness can produce atmospheric fades easily exceeding 10 dB. In these more common cases, impacts on FSOC systems may be severe. On the other hand, there are times when cloud fades may be as low as 1 or 2 dB as a result of thin, ice crystal based cirrus clouds. In these cases, the impacts on FSOC communication collectors may be limited. The ability to characterize the distribution and frequency of clouds are critical in order to understand and predict atmospheric impacts. A cloud detection system has been developed and applied to produce high resolution climatologies in order to investigate these impacts. The cloud detection system uses geostationary, multi-spectral satellite imagery at horizontal resolutions up to one kilometer and temporal resolutions up to fifteen minutes. Multi-spectral imagery from the visible wavelengths through the longwave infrared is used to produce individual cloud tests, which are combined to produce a composite cloud analysis. The result represents a high spatial and temporal resolution climatology that can be used to derive accurate Cloud Free Line of Sight (CFLOS) statistics in order to quantify atmospheric effects on optical communication systems. The Lasercom Network Optimization Tool (LNOT) is used along with a mission CONOPS and the cloud database to find configuration of geographically diverse ground sites which provide a high availability system.