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. Mitigating the effects of clouds to achieve reliable communications requires a geographically diverse set of ground receiver stations. 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 temporal resolution. Cloud detection is accomplished by modeling the radiance of the ground in the absence of clouds and comparing these to 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 find the optimal number and locations of ground stations for a given concept of operations. Applying LNOT to the JPL problem, we find that 90% availability could be achieved with 4-5 ground stations in the continental US (CONUS) and Hawaii. We also present the results of a pilot study that includes 6 months of cloud data over South America. We are continuing to expand our study by developing a global cloud analysis database, which will be used to identify the number and locations of global optical ground stations needed to achieve 90-97% availability. Currently, we are developing cloud detection capability over regions of interest in Europe, Africa, the Middle East, Asia and Australia based on the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) satellites: Meteosat-5, -7, -8 and NOAA GOES-9 imagery currently being operated by the Japanese Meteorological Agency (JMA)