That is Eagle Pass, TX. The infamous, massive border crossing area where suspected criminal border crossers are corraled under the bridge, where Elon visited, etc.
The jamming is done to make crossing the border without going through the checkpoint more difficult
TL;DR: It's weak signal, not jamming. The weak signal reports come from military training aircraft carrying out maneuvers that cause temporary signal loss.
So I'm a little skeptical on that front because military aircraft are still not that often broadcasting ADSB even during routine flights, at least in my (also close to the border) region. In theory the Air Force was supposed to have completed ADSB installation on their fleet last year but they blew the deadline pretty bad on even installing transponders, and of course they still reserve the right to disable them during military operations.
Maybe with the data we can figure out what portion of military flights are included?
For the helicopter training flights that I notice most often, it's still rare to see one that broadcasts ADSB, probably <10%. C-130s usually don't either here but it's more often, maybe more like 25%. Perhaps for other categories of aircraft they've installed more transponders. But in the city where I live, even passive mode-C MLAT is probably around 50% success on tracking military flights for ADSB Exchange. FlightAware might have better coverage for mode-C. mode-C can't contribute to this GPS reliability data anyway but it illustrates that even C-130 pattern practice is sometimes "stealth" from a radio perspective due to the low installation rates for ADSB and difficulty of good mode-C coverage.
The paper linked elsewhere (https://web.stanford.edu/group/scpnt/gpslab/pubs/papers/Liu_...) mentioned issues with military training flights resulting in spurious low-NIC cases but unfortunately doesn't quantify it. With the way the AF rollout has gone it probably depends on the specific installation, command, and aircraft type.
In the border region specifically we would tend to expect the majority of non-military flights to be civilian CBP aircraft that aren't performing unusual maneuvers. CBP has a somewhat complicated and limited authority to disable ADS-B that I don't know the contours of, I'm not sure how often they do so on their larger (non-sUAS) aircraft. Involvement of the Air National Guard in the Texas area might complicate the analysis though.
ATC is used to working with military aircraft without ADSB since it's been the status quo (and keep in mind that ADSB is not required on aircraft in general, although the set of airspace situations in which it's required has been expanded over the years to become a de facto near universal mandate). But the FAA doesn't like it, which is why they set the deadline for the Air Force to install ADSB, which the Air Force missed.
Military aircraft on military maneuvers don't deal with FAA ATC, the military has its own controllers. It's mostly an issue when they're operating near civilian airports (or the many, many military facilities that share an airfield with an airport). There are still adverse safety impacts to the lack of ADSB on many military aircraft, in that it defeats things like TCAS.
Actually this topic is slightly complex and I think a lot of people have misconceptions, so let's lay it out. These rules have gotten stricter and stricter in recent years.
1. ADSB is not required. Meaning, there is no universal requirement that aircraft be equipped with ADSB, and plenty of aircraft still legally operate without.
2. ADSB is required in class A, B, C, in many cases in class E, and within the "Mode-C veil" surrounding major airports.
3. ADSB is required in any case where a transponder is required, for those edge cases that are not included in the above.
4. The result is that the areas in which you can legally operate without ADS-B are mostly limited to low altitudes in rural areas. Of course, this encompasses a large portion of hobby aviation especially, but not very much commercial flight.
I can say that in San Antonio where I live and also operate a ADSB receiver the dedicated air force flight trainers (T38 Talons and T6 Texans) routinely fly with ADSB on. The C5 cargo plans also fly with ADSB on when doing training but I've seen non-training flights fly overhead with ADSB off.
I can actually receive high flighting planes over Del Rio so it would be interesting to see if they are reporting bad NIC values.
I thought Mode C was just barometric pressure data measured by the aircraft. It's related to altitude, not position, so there's no such thing as Mode C "coverage".
e; oh wait you said passive MLAT off Mode C, that makes more sense then
Yep, this map doesn't show jamming. It shows weak signals, of which jamming is one potential cause. An airplane pointing their GPS receiver at the ground will also cause a weak signal.
How does an airplane "point their GPS receiver at the ground" (for an extended period of time since a combined GNSS/INS positioning solution, which is what all airliners use at this point as far as I know, will need an extended signal loss to report decreased accuracy)?
From the FAQ, it sounds like they simply presume that anywhere with multiple low NIC values is indicative of interference.
> The GPS interference data is derived from NIC (navigation integrity category) values that we receive as part of the ADS-B protocol. We mark regions as affected if a significant number of flights in that area report lowered NIC values.
Unfortunately some of the data that's most directly applicable to determining aircraft attitude, like roll, is optional and rarely sent by aircraft, but yes I'm sure you could do a decent job of inferring maneuvering from change in heading and vertical rate (especially if you're looking at ADS-B data with high temporal resolution vs., say, every 10-60 seconds.)
on a pure radar scan, what would return of formation flying like this look like to a radar operator? is it just one large dot, or can they distinguish the number of planes in the formation?
That's a good link (that I should have posted). I suspect that some of the yellow (maybe even red) hexes in the U.S., and maybe some in Europe too, are due to that effect.
For people doubting that aircraft maneuvering can affect navigation accuracy as reported by ADS-B, I found a fun example. Around 1300 UTC today (0800 Texas time), 4 T-38s took off from Laughlin AFB for what looks like training, with lots of maneuvering. This link shows what it looks like when mapped in 2D: https://globe.adsbexchange.com/?icao=adffc3,adfff9,adffd2,ae...
If you click on the track, you can inspect the ADS-B data at that point in time in the sidebar on the left. If you scroll to the bottom of that sidebar, there's an "ACCURACY" section, that shows the Estimated Position Uncertainty (EPU). You can see it change from better than < 30 meter uncertainty to > 18.5 km(!) uncertainty as it performs the maneuver.
I made a video that shows how to see those values, and also shows the maneuver in a 3D viewer so you can see how steep the dive is (it's steep!): https://www.youtube.com/watch?v=jfHlpnEdHxw
(The viewer uses a generic aircraft model, FYI, don't be distracted by that.)
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