An Integrated Atmospheric Analysis Observing System in Support of Free Space Optical Communications

Free Space Optical Communication (FSOC) increases bandwidth by an order of magnitude over traditional Radio Frequency (RF) transmission. As near-Earth, deep-space satellites and aerospace applications support advanced technology instrumentation, the requirement to communicate large volumes of data makes FSOC an attractive alternative to RF. However, despite its considerable attributes, FSOC has tremendous sensitivity to atmospheric conditions, notably clouds, aerosols, and optical turbulence. Most clouds, even optically thin cirrus routinely cause atmospheric attenuation of several decibels making it nearly impossible to close an optical link. Having the ability to accurately describe the characteristics of the atmosphere in the line of sight (LOS) is therefore critical.

The installation of an optical ground station to test geostationary to ground communications is underway at the 3000 meter summit of Haleakala, Hawaii. To compliment the ground station, an integrated, atmospheric observing system is being built. The identification of a cloudy or clear LOS must first be evaluated along with its associated cloud top height (CTH). The detection of clouds in the sky-dome around the site is accomplished by the Cloud Mask Generator (CMG) which produces a high-resolution, two dimensional cloud/no-cloud decision based on the multi-spectral GOES satellite data in real-time at 15-minute, 1km (visible), 4km (infrared) resolution. Determining the height of the clouds detected at the site is essential as many clouds around the site do not exceed the summit height of 3052 meters and therefore would not impact FSOC. The Cloud Top Height product (CTH) is based on a combination of infrared temperatures from GOES, an atmospheric sounding from Hilo, HI and the Real Time Mesoscale Analysis of the surface temperature. Because of the limited horizontal and temporal resolution of the current GOES satellite the observing system will be augmented with in situ measurements. A calibrated, infrared, Whole Sky Imager (WSI) and a lidar will be deployed to provide day/night LOS characteristics of clouds and information on cloud attenuation. This integrated and enhanced observing system will be valuable in assessing the characteristics of the LOS and provide communication engineers the necessary data to define link performance characteristics.

This paper and presentation will show the status of this unique integrated observing system with high resolution visualization animations from the Whole Sky Imager as well as LOS characteristics.