It's not at all comparable. ADS-B is opt-in: you place an ADS-B out transmitter in your plane and turn it on to transmit your position [1]. You're perfectly free to turn your ADS-B off if you like. It's not even required for most of the US, so some planes may not have it installed (ADS-B out is only required within 30 nautical miles of a Class B airport [big airport], inside Class C airspace [medium-size airport], or in Class A airspace [18,000 ft above sea level]).

Military aircraft don't use ADS-B out a lot of the time. Spy planes are obviously not going to transmit their locations. A civilian plane with an electrical failure might stop transmitting ADS-B out. Being able to identify planes via satellite is a whole separate capability.

[1] In all the planes I've flown, ADS-B is configured to transmit whenever the master electrical switch is turned on, but it can be configured to be turned on and off at will. See this video on a mid-air collision involving an eccentric character who liked to fly with ADS-B out turned off: https://youtu.be/G5y3JiOEnVs?si=rs5gNMurZ9ssUloS. If I recall correctly, he had his ADS-B wired to his nav lights so he could turn it on and off at will.

From my experience in general aviation, I've never met anyone who intentionally turned off their ADSB. It is generally wired into the transponder, and the bulk of air traffic worldwide happens where a transponder is practically required. Yes, it is technically not needed but you can't get help from ATC, can't fly instruments in the clouds, and you can't fly high.

Sure, it can happen but these are edge cases. Space-based ADSB solves this problem with a fraction of the effort and much better data. Spooks might need this for military stuff, but for the bulk of planes, it doesn't make sense.

You are NOT at all (legally) free to arbitrarily turn off your ADSB on an aircraft equipped with it. 91.225(f) [1].

> Except as prohibited in [unmanned aircraft section], each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times unless [authorized by FAA or ATC].

A common way to add ADSB to an aircraft not originally equipped is replacing one of the lights with a uAvionics skyBeacon[2], which has a LED light + ADSB-out transmitter. So the nav light switch would control it, but you'd also now be required to have them on at all times.

[1]: https://www.ecfr.gov/current/title-14/part-91/section-91.225...

[2]: https://uavionix.com/products/skybeacon/

There's a whole world outside the USA which does not follow FAA regulations. I, flying an unpowered glider, turn mine on only when I need a clearance.

That's nice, but the parent explicitly cited part of US regulations where it's required, while ignoring that it's always required if equipped.

Can’t see past the wall?

ADS-B is mandatory in many jurisdictions and for all commercial flights basically everywhere. Obviously like any transponder, you can pull the breaker, but turning it off is likely to beer the end of you're commercial piloting career.

That video is great, thanks. Though the ML solution doesn't seem to claim to be able to identify individual aircraft, just do daily counts of aircraft at specific airfields. Which I guess works for military aircraft, but I guess if you're a nation state actor you've already got this sort of technology/intelligence?

Nation states are always interested in paying less to get this sort of intelligence though.

Authentication? ADSB isn’t authenticated. Anyone can emit, anyone can spoof, and I probably shouldn’t say that over the wire. The FAA said in 2012, when the conf at Defcon was made, that it had its own secret mitigation.

Getting the Doppler shift right against multiple receivers would be physically impossible

(If you’re not travelling at the right speed of course)

Agree on ADSB, but couldnt you spoof this using paint or 1:1 scale cardboard aircraft?

I was wondering about that too. They can only detect aircraft with wingspans over 25 m, so most fighter jets (and also GA aircraft) are too small. Large commercial aircraft can be much better located (and identified!) via ADS-B. So that doesn't leave a lot of aircraft (bombers, tankers, AWACS and other larger military aircraft) for which this is useful.

Mentioning the military might give you a hint...

I mean, commercial services do filter out mil adsb, but they are out there and available. So the use case is tracking movements of military aircraft?

Not all military planes are going to actually have ADSB, obviously. Also even the unfiltered stream requires an ADSB receiver somewhere.

Yes, that's true, but I'm still struggling to understand the market fit for "where are the military aircraft". You would presume the people who need to know this information (ie those people for whom this is actionable data) already know this to a sufficient degree?

They do. Until people who have this information decide to stop sharing it with you.

In my experience, military aircrafts are visible in flightradar most of the time. However, if they are flying in a group (e.g. choppers), usually only one of them is visible.

It's not true that commercial services filter out military aircraft with ADS-B. In fact, FlightRadar24 even lets you filter to only show military aircraft. I see over a dozen flying near San Diego right now.