Sovereign airspace seems to me should be a bit like 12 mile limit for oceans or 200 mile economic zones for oceans.
So how far up? 12 miles? If it is a segment the shape of the continent + 12 mile ocean limit, does it reach out into space? Once the air becomes thin (and cold) enough to not support life is that the limit?
Apparently you can have balloons in the stratosphere, is that sovereign airspace?
These signals a balloon can pick up it they are important surely they will be encrypted.
I seem to remember in the sixties or seventies there was a picture of a Russian reading a newspaper in red square and you could read the newsprint.
If satellite technology hasn't improved in the 50 years since, I would suggest that neither has balloon spying.
How many mega pixels is your phone?
It's the ability to pretty much hover for a while that makes it different. Considering how fast recon satellites fly past overhead (literally a single blink to cross your entire field of view), according to those green laser videos that have been showing up lately), they can capture a lot more targeted info with a balloon, and quite cheaply for that matter.
