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.
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.
Airplanes have ADS-B, which is quite similar to the maritime AIS location broadcasting. The only significant difference is that satellite AIS coverage is high and ships don't go fast, so having no signal for a few hours is not as big a problem for ships.
ADS-B satellite coverage is currently provided by (at least) the iridium constellation, but that only came into effect in 2016.
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).
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 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.
ADS-B has the same problem -- it's hard to collect it over the oceans.
Satellites do pick up the signal, but the detection area is pretty wide, so sometimes it's just too many signals coming in all at once, overwhelming the satellite. ADS-B is also pretty chatty, so the data sizes are significant (compared, to, say AIS, which is a similar system for marine vessels).
It's gradually becoming better, satellites having more focused antennas able to gather signals only from unpopulated areas, and more computing power to filter noise out.
Iridiums is rolling out new satellites that have ADS-B receivers on board (for open ocean data collection), and will be providing this data to the FAA for a fee. Its a solved problem, but will take time to roll out.
They have a GPS beacon. The ADS-B system is exactly that. It just stopped transmitting. Apparently it can be manually turned off from the cockpit. Or it malfunctioned.
Out of curiosity, how is reception different? Basically, I'm wondering if it would be worth adding an AIS receiver to the ADS-B that I'm feeding to a couple sites already.
E.g., do you need line of sight? I'm a couple km from water, not quite 100m elevation.
Automatic dependent surveillance – broadcast (ADS–B) is a cooperative surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked.
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