Rob wrote:

For some time now I have been looking for a correct definition on how
to compute global radiation. I have a number of parameters, which
could be used such as downward and upward short & long flux. However I
have not been able to find any helpful information. Would anybody be
able to help me with either a mathematical equation and or some other
definition in order to calculate global radiation derived from other
parameters??

Thanks a million

Which other parameters ? This can be an easy or very difficult problem
depending on the accuracy desired and which part of the spectrum considered.
The clear sky problem is generally rather accurate, but clouds greatly
complicate the matter. Obstructions to the horizon also may be a
consideration.