Mitigating the impact of clouds on Optical Communications

NASA Jet Propulsion Laboratory (JPL) is interested in adding optical communications to its deep space communications network. Clouds adversely affect the transmission of optical communications; in order to mitigate the effects of clouds and achieve reliable communications, a geographically diverse set of ground receiver stations is needed. To study cloud effects on optical communications we have developed a high-resolution cloud climatology based on NOAA Geostationary Environmental Operational Satellite (GOES) imager data. The GOES imager includes multi-spectral channels, one visible and four infrared, at 4-km spatial resolution and 15-minute time resolution. Cloud detection is accomplished by modeling the radiance of the ground in the absence of clouds and comparing the actual radiance values from the imagery. A composite cloud decision is formed by objectively combining the results of the tests from the individual channels. Ground site selection studies are accomplished using the Lasercom Network Optimization Tool (LNOT). LNOT applies a discrete optimization algorithm to the cloud climatology dataset to .nd the optimal number and locations of ground stations for a given concept of operations. Applying LNOT to the JPL problem we find that 90% ailability could be achieved with 4–5 ground stations in the continental US and Hawaii. We also present the results of a pilot study that includes 6 months of cloud data over South America.