I retired from the USAF in 1979. For twenty years I worked with some rather varied projects.
1) Microwave "bombardment" (if we wish to call it that) is well known. Thirty, forty years ago, maybe longer, bugs were used which were difficult to detect because they were not active unless a specific microwave signal was aimed at the location of the bug (obviously from outside the building).
That signal activated the pickup (bug) only so long as the signal was active - letting the surveillance effort (in effect) turn the bug on and off. There's more, but believe me this is decades-old technology.
2) For decades, the U.S. Navy has used VLF frequencies to communicate around the world to fulfill specific tasking unique to the Navy. Such antenna fields require many acres of land and put out heavy wattage fields. There was debate about the affect of such VLF high-wattage antenna fields on people and animals in the 1960s.
3) OTH (Over The Horizon) radars have been used for decades. You would not believe the distance and resolution such radars provided twenty years ago. They've improved.
4) I've never worked with the weather radars on TV. But I've noticed when our boy wants to show exactly where the storms are, he can expand the desired area to show objects less than a city block. Weather radar. Can you imagine what our military/intelligence efforts can do?
5) Check out Microsoft's Terraserver for some interesting flicks:
http://terraserver.microsoft.com/default.asp
Look at the dates on some of the overhead photography. This was NOT the best photography available in the 1960s and 1970s.
I worked for the Census Bureau in 1990. You would not believe the information I had, as a field interviewer. They knew where every building was - including outhouses! Honest! Imagine what can be done now.
6) Big Brother is big. He doesn't need to track gun owners - most are irrelevant to his interests. But from time to time in the news we hear that certain groups have been infiltrated by operatives of our government. Which groups, how many groups, and other such questions are answered only on a "Need to Know" basis.
If you'll remember, the federales had a complete topographic model (in living color) of Ruby Ridge (with cute little buildings, roads, trees, etc.) before they invaded.
7) Question for you. When there is a DEcrease in the number and or importance of foreign surveillance targets, do you think the shops cut back, phase out workers, or "economize"?
Right! New threats, foreign and/or domestic, magically appear and "require" investigation and monitoring. (Simple facts supporting career progression.)
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Big Brother has the ABILITY to watch any of us in ways we would never even detect. But why would he do it? Remember, these feather merchants must justify the huge expenditures of resources involved with such studies and surveillance.
Unless and until owning guns becomes illegal, we probably don't have much to worry about. However, if valid intelligence targets become few, and we (as gun owners) attract the interest of Big Brother, then it could be a much different story.
RKBA!