Tracking from Above It's difficult to use radar in urban environments because of all the structures that get in the way. But by bouncing highly sensitive radar off of buildings' facades, DARPA hopes to lock onto individual vehicles from UAVs and track them through urban streets even when buildings block line of sight. Zemlinki From Popular Science:
Radar is great for tracking objects in the wide-open sky or even at sea, but when you try to take it to street level you run into some obstacles -- literally. Radar requires a good line of sight, and obstructions like buildings or terrain features can render radar useless. But now, using a handful of unmanned aircraft and technology that allows them to intelligently reflect radar off buildings, DARPA is developing a system that should be able to track individual vehicles even as they dart between skyscrapers and other structures.
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My Comment: You can run .... but you cannot hide.