Initial comparisons of forecast attenuation and beacon measurements at 20 and 40 GHz

The use of frequencies above 20 GHz for Earth-Space communication has many advantages, primarily substantially increased capacity. Unfortunately at these frequencies the attenuating effects of the troposphere become very large; clouds, rain and atmospheric gases all contribute significant attenuation. The Italsat propagation experiment demonstrated the large fade margins that would be required to achieve a high availability network. At the University of Bath we have developed a technique that is able to forecast link fades (in terms of cloud attenuation, rain attenuation and the attenuation from water vapor and gaseous oxygen and an estimate of the scintillation variance) a number of days into the future. This technique exploits concepts from numerical weather prediction (NWP) systems in order to characterize the meteorological environment. A propagation model is then applied to forecast the fade level.