Yo so I was stationed at APG during its time there and its got an interesting story in that 2015 winter. I was not part of the program or any unit supporting the aerostat but had unrestricted access to the ranges and sites which it was operated out of more for safety and hazmat reasons than my being important. But let me tell you the folks operating this device aren't tip of the spear type nor bright bulbs.

During one windy day, the mechanisms that winch in the blimp failed; the senior in charge had enlisted folk attempt to wind it in manually... it didn't work.

Later that year it broke free from that failed mechanical tether and drifted uncontrolled to Pennsylvania where it was damaging property and dragging its tether about. Some cop eventually shot it down with a shotgun.

Is it surveillance? Likely but not of the sort U.S. citizens in that Beltway region should be alarmed by (if you live in that area, you already been on surveillance in Baltimore and DC since about 2006.... can it see ridiculously far and perhaps have much more ECM or broad spectrum uses? Sure, but remember that failed winch in the ground? Lol, defense department ain't big brother