Hi, I did this. The link that was posted doesn't include presenter notes by default, which is leading to some confusion. Check out https://docs.google.com/presentation/d/1sowJrQQfgxnLCErb-CvU... instead.

IIRC the term the FBI used to describe these activities was "confidential", which is why they registered the planes to front companies they made up. Congress wanted to know more, so the FBI gave them a confidential briefing (https://apnews.com/article/1240a8a42edf4a86aff72a0246525a95):

    The FBI assured Congress in an unusual, confidential briefing that
    its plane surveillance program is a by-the-books operation short
    on high-definition cameras — with some planes equipped with
    binoculars — and said only five times in five years has it tracked
    cellphones from the sky.

    The FBI would not openly answer some questions about its planes,
    which routinely orbit major U.S. cities and rural areas. Although
    the FBI has described the program as unclassified and not secret,
    it declined to disclose during an unclassified portion of a
    Capitol Hill briefing any details about how many planes it flies
    or how much the program costs. In a 2009 budget document, the FBI
    said it had 115 planes in its fleet.

In case you missed it, pretty much the first place I posted about what I'd found was here at HN (https://news.ycombinator.com/item?id=9508812).

Since then, I've done some other stuff in a similar vein.

I created the Advisory Circular network of twitter bots that post, in real-time, whenever they see aircraft circling (https://twitter.com/lemonodor/status/1294002338215034880). The code is all open source. The bots have helped me (and hopefully other people) discover all sorts of interesting things that aircraft are doing, often right over our heads: power line inspections, dropping sterile fruit flies, tests of new military technologies over the Mojave desert, retired attack helicopters fighting fires, and more.

ADS-B data includes information about navigation accuracy, and it turns out it's pretty easy to see when an aircraft is experiencing GPS/GNSS interference, and even map it. I created GPSJam (https://gpsjam.org) to make that data accessible to the public (instead of, say, paying tens of thousands of dollars to geospatial intelligence companies). On that map you can see things like conflict zones, U.S. military tests and training in the Southwest, and Russia's concern over increased risk of drone strikes deep into their territory.

The coolest thing about all this stuff is that it's not really very hard to do. It turns out as soon as you start paying attention to aircraft over the course of days, and weeks, you immediately find mysteries to solve.