ADS-B signals (from my limited knowledge) are transmitted by aircraft showing some basic data like location, altitude, speed, callsign, aircraft model and a few other things. They only have a range of a few hundred kilometers so a website that does flight tracking using a global network of (volunteer) receivers, it's a step in their coverage to be picking up signals over the oceans.
Aircraft broadcast ADS-B signals which contain tracking information, which is used by live flight trackers to map out each flight in real-time. The problem is that there are large blind spots when aircraft go over oceans due to the lack of receivers, so this is intended to increase coverage.
ADS-B is an automatic broadcast of an airplane's position and velocity, intended for making management of the airspace easer, among other things. It is not encrypted, and you can set up the hardware to receive the signal with a modest amount of effort. There is apparently a website somewhere where these hobbyists are aggregating this data.
How do it get ADS-B data from over the oceans? I guess it isn't satellite (which I now is used for actual tracking) since there is obviously a lot less lines over the oceans (but lines nonetheless).
Sorry I'm not sure what you mean, as I understand it, the ADS-B signals are just being acquired with a receiver on the 'boat' and then relayed via satellite.
We are now doing that. Planes with ADS-B send out their position, altitude, direction and speed every eight seconds. That's how flightradar24 tracks most airplanes. ADS-B has been introduced sometime in the mid-2000s, and became mandatory in many countries in 2020. It originally depended on ground receivers or other aircraft picking up the transmission though, which is an issue if a plane goes missing in the middle of an ocean. This seems to be mostly solved now by satellites equiped with receivers.
Oh that's interesting, thanks. So I guess it's similar to ADS-B exchange[1] and the like but for ships.
Have you operated an antenna, by chance? I've considered building an ADS-B receiver to satisfy my curiosity about the planes I see out my window all day.
ADS-B is essentially mandatory nowadays, but it's just a radio that transmits location to others in the same local area. Get enough volunteers with receivers spread throughout the world and you do get real time location tracking of every aircraft. See https://www.adsbexchange.com/
That's a lot of data to transmit via satellite and satellite bandwidth is expensive. Most planes don't crash into the middle of the ocean with all of the transponders turned off so it's an expensive solution for a very rare problem. Satellite-based ADS-B seems to be the future going forward. Everyone can see a plane out in the middle of the ocean and can immediately know where to look if it happens to go down.
I track several of these aircraft a week, and they usually don't have ADS-B. I track them via multilateration, combining my receiver's data with data from several other receivers (as part of the Flightaware network: http://flightaware.com/adsb/)
In what is probably the biggest case, FlightAware, a lot of the data comes from a fleet of users running ADS-B[1] receivers feeding data into their system. ADS-B data is what Air Traffic Control uses to track planes, and it's receivable using using a cheap TV tuner and a raspberry pi[2]. It ends up being probably the best way to track planes very precisely, as long as you can get enough coverage, which flightaware manages to do pretty well [3]. They then package this data and sell it via an API/tools for Fixed Base Operators or apps like Just Landed.
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.
I think the author is a bit confused by how this technology works. My understanding is that an aircraft can also have an ADS-B receiver onboard, which allows the pilot to identify other traffic in the local area - it doesn't rebroadcast the signals as in a mesh network (I don't think there is any encryption in these signals either, so that's probably a good thing).
ADS-B is only really used currently as a secondary resource for identifying aircraft rather than seeing where aircraft are. The primary way is by using a radar return, and matching this up with the aircraft transponder which reports the aircraft ID and altitude.
At the moment I don't think there are any hard requirements on having ADS-B transmission equipment on aircraft, although most commercial airliners already have it (which is what FlightAware and such usually use - at least outside the US). It will become a requirement over the next few years however for most civilian aircraft.
there is a 250-400 km range for FlightRadar, it does not cover oceans very well.
http://www.flightradar24.com/how-it-works
"Flightradar24 has a network of more than 3,000 ADS-B receivers around the world that receives plane and flight information from aircraft with ADS-B transponders and sends this information to our servers. Due to the high frequency used (1090 MHz) the coverage from each receiver is limited to about 250-400 km (150-250 miles) in all directions depending on location. The farther away from the receiver an aircraft is flying, the higher it must fly to be covered by the receiver. The distance limit makes it very hard to get ADS-B coverage over oceans."
Sometimes it leaves ADS-B enabled to send a message. During the evacuation of Afghanistan there were B-52s over Kabul that could be tracked on Flightradar24.
Flightradar24 works on the premise of volunteers providing ground stations to decode ADS-B transmissions from the aircraft.
Two variables here:
1) ADS-B Transmissions are line of sight, so once you are far enough off shore there are no ground stations to receive the data
2) Ground stations are provided by volunteers, so there isn't a critical mass of volunteers that provides 100% coverage over even ground locations
Also it's just cool.
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