This is an idea I've been playing with for a while. It's still under development, but the basic technique is similar to the one snipers use to search and detect targets.
One of the skills we learned at the scout/sniper school was the detection of targets. We would lay on our bellies and try to find hidden objects that the instructors placed in the field via the use of scopes. We also needed to detect an instructor acting like a sniper.
All the objects (or potential threats) were hidden in a large piece of land, some close and some far. It would have been almost impossible to randomly start scanning for the targets in such a large area, so a simple technique was used: begin scanning with the naked eye for objects near and from left to right, then move a bit farther from right to left, etc. Once you get to a point where the naked eye is not good anymore, use a scope.
Essentially you create a grid on the area where you move from close to far and from left to right and scan each sector for a potential threat, then you log everything you see.