Mentioned earlier the relative importance of rain vs. cloud depending on the availability sought for the system. Point of difficulty for development of prediction methods – to know where the cross-over point lies in terms of %age availability, or %age time, at which rain will dominate over cloud, or vice versa. How are both allowed for at the cross-over?
Correlation of rain in two different locations; rain can be confined to a particular area so that two microwave links, or two satellite links, with different azimuthal directions and/or elevation angles may not be equally affected by a rain event. This is principle of diversity. But need to know what correlation exists between rain events on two paths:
to optimise a diversity system, e.g. spacing of terminals
in interference assessment - if a wanted signal received at a terrestrial station is attenuated by rain, will an interfering signal on a different path, e.g. a satellite path, be equally affected?
If events are highly correlated, then there will be no increase in interference potential; if poorly correlated, interference potential may rise.
