Actually, let's think about this. It does not extend to the surface, so whatever aircraft it's protecting has to be able to make it there without the security cordon. That means it's not VIP transport, which would be inverted from that. Also means that it's not for anything tethered, like a balloon. Or anything originating from the ground, like rocket or artillery fire. Whatever it is, it's landing and taking off somewhere else.
The 3500' seems suspiciously like it's putting 500' + rounding over the highest obstacle, at 2875'. That suggests the aircraft is maneuvering. So does the large swath of selected air, all the way up to 18,000. If the aircraft can climb to 18,000 and do so inside that small space, it's probably a turbine, probably a fixed-wing, and probably fairly high performance.
Given that you're allowed to enter with a code means whatever it is can be engaged by ATC in some fashion. Also suggests that it will not be a live-fire exercise of any variety, as less than five miles is not enough to contain that.
I would assume it's military or police. Could be piloted, could be a drone. I'd probably put my money on a drone test of some sort. DHS, maybe?