Great stuff, very thought provoking, so very many thanks to all (and especially to Biggin and Smiler).
So surveillance is the broad activity of 'keeping tabs on the enemy' in an overview kind of way, and as such encompasses intelligence gathering, observation (which is focused on a specific defined geographical area or element), targeting and reconnaissance.
So what is intelligence gathering? What is reconnaissance?
I need a set of definitions that define and differentiate.