> As part of the ADS-B messages we receive from each aircraft, the Navigation integrity category (NIC) encodes the quality and consistency of navigational data received by the aircraft. The NIC value informs how certain the aircraft is of its position by providing a radius of uncertainty.
> Poor NIC values alone might indicate a problem with an aircraft’s equipment or unfavorable positioning. However, when observed in multiple aircraft in close proximity during the same time frame, it suggests the presence of a radio signal interfering with normal GNSS operation.
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.
The GPS jamming map linked to in the article[1] discusses this somewhat, in the "About the data" box:
- ADS-B messages include position information from Global Navigation Satellite Systems (GNSS), like GPS, Galileo, GLONASS, BeiDou, etc.
- It is not possible to directly measure GNSS interference, but we do calculate the NIC (Navigation integrity category) for ADS-B messages.
- The NIC value encodes the quality and consistency of navigational data received by the aircraft.
- Poor NIC values alone might indicate a problem with an aircraft’s equipment or unfavorable positioning. However, when observed in multiple aircraft in close proximity during the same time frame, it suggests the presence of a radio signal interfering with normal GNSS operation.
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.
(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.
"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).
The ADS-B signals that many aircraft broadcast include not just the aircraft's GPS positions, but also a measure of GPS accuracy (strictly speaking, ADS-B doesn't talk about GPS specifically and can handle any sort of navigation technology; I'm sure there are some planes out there reporting positions based on inertial navigation systems, with correspondingly low accuracy, or GLONASS-derived positions, or whatever, but my understanding is that right now something on the order of 99% of aircraft with ADS-B are using good old GPS so I'll just keep using the term GPS in this description). If you go to https://globe.adsbexchange.com and click on just about any aircraft, you'll see an info sidebar on the left of the screen. Scroll down until you see the ACCURACY section, and you'll see values labeled NACp, SIL, NACv, NICbaro, and Rc. Those are all self-reported measures of the accuracy of the data being sent by the aircraft[1]. NACp is "Navigation Accuracy Category for position", and is a good measure of whether the aircraft's GPS is working well. (A somewhat obscure feature of ADS-B Exchange lets you see a map of all aircraft that are currently reporting poor navigation accuracy for their GPS: https://globe.adsbexchange.com/?badgps)
To make the maps, I process a day's worth of data from ADS-B Exchange to find all the aircraft reporting poor navigation accuracy and then I color map hexes (using H3 hexes) according to the proportion of aircraft passing through that hex that reported bad GPS accuracy. Specifically, I'm counting an aircraft as experiencing "interference" if it at some point reported good navigation accuracy and then reported low accuracy. Doing this helps filter out aircraft that just have an ongoing issue with their GPS equipment, or don't even have GPS.
When I do that, areas where there is systematic interference—almost always jamming by military systems—become obvious. There are a few conflict zones (Syria, Cyprus, Israel) that have been experiencing jamming for years, and the U.S. often has smaller scale military testing, especially in the West and Southwest. You can also see the jammers that are apparently setup around Moscow to prevent drones from flying near Oligarch dachas[2].
I started making these maps in February before Russia invaded Ukraine because I thought it might provide an early warning of an invasion. I didn't see that, and in fact this technique doesn't do a very good job of mapping GPS jamming around the actual war zones because civil aviation stopped over Ukraine, so there are zero or few aircraft with ADS-B reporting their GPS accuracy[3]. Without that data, I can't make a map.
Sometimes I do see changes, like when Russia suddenly started jamming around Kaliningrad in March 2022, causing interference in many Baltic states and leading to Finland to cancel some flights[4]. Then a few days later, they just stopped.
I don't think too many people have realized yet what an amazing source of GPS interference data is available using ADS-B! It's like having thousands of sensors roaming the planet, broadcasting GPS accuracy data every few seconds. I sometimes wonder if I would disrupt someone's nascent business model if I started publishing my maps regularly.
> Because airplanes broadcast their GPS position via ADS-B, you could also know that you'd succeeded.
If the GPS is integrated with inertial navigation systems, the effect of GPS spoofing on the computation of the position (that could be observed by ADS-B) might prove tricky to anticipate.
It only counts aircraft as experiencing interference if they have previously reported high navigation accuracy on their flight, and then begin reporting low accuracy. It's not going to just show places where INS drifts. However, it may show areas, typically military, where aerobatics or hard maneuvering are taking place, which can mask an aircraft's GPS antennae from the satellites.
Just a note from the sites FAQ: the data is actually showing places where airplanes report LOW NAVIGATION ACCURACY via their ADS-B transponders.
Since planes tend to default to INS navigation with use GPS, GLONASS, Galileo or other systems to supplement the drift, it may be subject to certain data skew (e.g. if there's an area on the world where most planes aren't equipped with GPS navigation system, have poor quality navigation tech or you might be seeing "jamming" where there might just be a common place on airline route where INS drifts).
So then if everything goes to ADS-B and GPS, doesn't that create a potential single-point-of-failure scenario, as isn't the data that ADS-B sends out itself derived from GPS? Having all navigation information come from a single source strikes me as about a good idea as the single AoA sensor on the 737MAX.
I'd like to be wrong about this, but I'm not sure how I am. How am I potentially wrong about this?
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.
It seems related to an upgrade on that Collins equipment, in the Receiver Autonomous Integrity Monitoring, and quality of nav data sent to ADS-B equipment, which is downlinked from the aircraft to air traffic control.
The Multi Mode Receivers aren't strictly GPS units - they also get nav signals from terrestrial VOR, DME, and ILS stations. DME - DME fixes are qite precise, but not as precise as GPS positioning.
There's also an altitude restriction on affected aircraft: they aren't permitted into airspace using Reduced Vertical Separation Minimums, where tighter navigation and monitoring restrictions apply.
A lot of comments seem to be about spoofing. Remember that there are multiple humans in the loop -- experienced pilots and experienced air traffic controllers -- and multiple levels of redundancy. Pilots have access to barometric altitude, radar altitude, traditional VHF navaids, TCAS-issued resolution advisories (based on directional antennas, not GPS)... in addition to GPS. Air traffic controllers have primary radar and secondary radar in addition to ADS-B information.
You could probably cause a lot more trouble by buying an aviation radio off the shelf and just chatting on the frequency or issuing fake clearances if you want to be a mass murderer.
Ultimately the system comes down to many systems working together, not one stream of commands between two computers.
Yeah, ADSB is a position reporting system that has to work between aircraft with no prearrangement. Such a thing is inherently insecure by the nature of what it is.
What I don't understand is how this is supposed to work when the point of using the more precise GPS-based ADS-B positional reporting is for controllers to be able to pack airplanes closer together. If they do this, there will literally not be space in the sky to spread out existing air traffic to radar-based separation requirements.
> Their calculation needs to know where the plane really is [...] but you don't know in the real world
ADS-B Out from the aircraft will give you a pretty good idea where the aircraft is. Whether it's accurate enough for this attack is hard to know without doing some research, but it does transmit position.
What is MLAT in this case? The planes transmit their location in the ADS-B message. They are filtering a lot of redundant message receptions from multiple receivers. I would assume the messages also include altitude and heading information, so locations can be predicted between message receptions.
> As part of the ADS-B messages we receive from each aircraft, the Navigation integrity category (NIC) encodes the quality and consistency of navigational data received by the aircraft. The NIC value informs how certain the aircraft is of its position by providing a radius of uncertainty.
> Poor NIC values alone might indicate a problem with an aircraft’s equipment or unfavorable positioning. However, when observed in multiple aircraft in close proximity during the same time frame, it suggests the presence of a radio signal interfering with normal GNSS operation.
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.
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