I can't remember details but I'm positive I've read about such a capability being developed in the 70s or 80s. I think it was an airborne radar system similar t

I can't remember details but I'm positive I've read about such a capability being developed in the 70s or 80s. I think it was an airborne radar system similar to AWACS except looking at the ground, combined with computer systems that would analyze the data to identify troop movements. With the military resources available today (drones, satellites, ...) and the massive increases in computing power it wouldn't surprise me if they track troop movements in near real-time.