I've been working on mapping GPS jamming using ADS-B data for a couple
years, and I'll try to address questions and points brought up here
based on what I know.

Relevant previous posts on HN:

2022: https://news.ycombinator.com/item?id=32245346

2023: https://news.ycombinator.com/item?id=37868106

(From my comment on that 2023 post: "Why haven't FlightRadar24,
FlightAware, or any of the other flight trackers done this?")

"A single observer can't really say for certain that jamming is
happening; you need a distributed sample from multiple different
sensors over a period of time to have reasonably high confidence."

There are heuristics you can use that allow you to make a pretty good
guess about whether jamming is happening based on signals from just
one or two aircraft, and have worked well on GPSJAM for the past
couple years.

With regard to localization of GPS jammers, yes you can do direction
finding of the emitted signal directly, but that's easy mode. For a
fun challenge, do it based just on observations of the ADS-B data from
affected (and unaffected aircraft). Here's one approach from
researchers at the GPS laboratory at Stanford, "GNSS Interference
Source Localization Using ADS-B data":
https://web.stanford.edu/group/scpnt/gpslab/pubs/papers/Liu_...

I have some other ideas about how to do that localization.

https://twitter.com/lemonodor/status/1764054377982308484

"Do aircraft systems really only use GPS and not the full
constellation of navigational satellite systems?"

ADS-B doesn't tell you what navigation system is, but my understanding
is that most aircraft are still using GPS. Maybe someone who works on
aircraft avionics will chime in. A few years ago I did see data that
distinguished between different GNSS, and GPS was experiencing more
jamming than the others. I assume as multi-network systems become more
and more common jammers will just target all of them, if they're not
already.

"There looks like a big hole of no data over Ukraine, where I'd most
expect GPS jamming, but I suppose there are no civilian flights
either. Maybe they could setup an GPS observation station on the
ground at a surveyed point to get data there."

That's right, no (or few) flights over Ukraine with ADS-B transponders
means no data. I actually first started mapping GPS jamming on
Feb. 14, 2022
(https://gpsjam.org/?lat=45.00000&lon=35.00000&z=3.0&date=202...),
because I thought it might give me an early warning of the expected
Russian invasion of Ukraine. It didn't work out that way--there was no
indication of interference right up until Feb 24., and then all civil
aviation stopped and there was no more data for that region
(https://gpsjam.org/?lat=49.18928&lon=33.51687&z=3.9&date=202...).

As some of you have noticed, GPS jamming is highly correlated with
conflict zones. Some conflicts are higher intensity than others--for
example, I think the airspace around Cyprus has been jammed for years
(since 2018 maybe?), and I get the feeling it's more harrassment than
anything else (maybe someone more geopolitically savvy than me knows
more).

"I see 2 red cells on the US/Mexico border right about Texas/Coahuila
region". Someone always says it's cartels, and the evidence is that
it's much more likely to be U.S. military testing and training. First,
the interference is always in the Laughlin and Randolph military
operating areas (MOAs) (https://imgur.com/vieGhgN). Second, the
interference usually runs during the week and takes weekends
off--which I doubt cartels do, but that's the typical pattern seen for
military exercises.

"am I missing any other GPS jamming mapping or data collection projects?"

From 2/24/2022 until 3/19/2024, gpsjam.org was the only site with
regularly updated GPS jamming maps. On Twitter, @auonsson
(https://twitter.com/auonsson) and @rundradion
(https://twitter.com/rundradion) have been posting geospatial and
other analysis of similar data for the past several months at least,
and @x00live (https://twitter.com/x00live) has looked at ADS-B and GPS
interference for a while too. (I'm not even going to try to catalog
academic or government efforts, though I will mention HawkEye 360's
satellite based GPS interference mapping:
https://spacenews.com/hawkeye-360-gps-ukr/)

"If line of sight to the jamming antenna is required to be jammed, why
do aircraft not have a downwards shield so that they only receive GPS
signal from the sky (satellites) and not from jammers (coming from the
bottom hemisphere)? Or is the jamming signal so many orders of
magnitudes stronger than the satellites that there's always going to
be some gain no matter how good the shield is?"

Yes, GPS signals are so weak (below the noise floor!) that it's just
super easy to overpower them with terrestrial (or airborne)
jammers. But there are special antennas and other techniques for
building jam-resistant systems, e.g. "controlled reception pattern
antennas" (CRPA):
https://www.gpsworld.com/anti-jam-technology-demystifying-th...
But I think the main reason most civilian aircraft systems aren't jam
resistant is because they didn't need to be--For the past several
decades GPS jamming has been a much smaller issue than it is now, and
I don't think there was sufficient reason to spend time and money on
what would have been an over-engineered, mostly unnecessary
system. But the situation is changing, and I expect anti-jamming to
become a more significant concern by equipment manufacturers and
aviation authorities.

[Edited to add:]

"I'm in the middle of one of the red blobs on the map and just used my
phone with google maps to drive around. It worked fine."

From the GPSJAM FAQ: ""I live in one of the red zones and my GPS was
fine?""
(https://gpsjam.org/faq/#i-live-in-one-of-the-red-zones). Yeah, the
answer is, as you mentioned, aircraft fly at higher altitudes, so they
get much longer line of sight to the jammer.

On the general idea of using ADS-B to map GPS interference, when I
thought of this idea I was pretty excited. I realized that if you had
access to worldwide ADS-B data, which ADS-B Exchange graciously gave
me as part of my Advisory Circular project
(https://news.ycombinator.com/item?id=24188661), you could also make a
worldwide map of GPS jamming, and I hadn't seen anyone do that before
(later I found some researchers who realized you could get GPS jamming
information from ADS-B, but they only looked at a couple
aircraft).

I just think it's pretty neat that even though there were multiple
companies devoted to processing, analyzing, and selling ADS-B data,
and ADS-B data is not all that complicated, none of those companies
had realized this new way of using it. Sometimes there's gold left
even in data that you think must have been completely mined out.

Even specifically looking at ADS-B data as it relates to GPS
interference, there's still lots to be done! FR24 is mapping jamming,
but I don't think anyone else has made worldwide maps of spoofing
(yet!): https://twitter.com/lemonodor/status/1770515361739493488

[Edited to add more:]

With respect to safety issues, yes, aircraft have redundant navigation
systems. But GPS is one of the important layers that add safety to
aviation, and it is not at all normal for entire countries or even
larger regions to lsoe GPS while still maintaining passenger
flights. This Eurocontrol presentation, "GNSS Interference and Civil
Aviation", has lots of details:
https://rntfnd.org/wp-content/uploads/Aviation-GNSS-interfer...

From the presentation:

Aviation Safety is built on two main principles:
• Trust your instruments
• Follow standard operating procedure
GNSS RFI causes pilots to have to question both principles!

There have been close calls due to lack of GPS. It increases workload
for both pilots and controllers, which is a safety issue by
itself. Despite a lot of airlines and government aviation agencies
saying everything is fine, they're not really prepared for a world
with frequent GPS denial, and everything is not fine. Industry and
government are organizing emergency meetings about how to handle this
in a less ad hoc way than they have been so far (commercial aviation
is kind of the opposite of ad hoc).