Hi people,

I apologise if this is not the right forum for this. This is the closest I can find on the Internet!
I am trying to figure out how the world of AIS tracking actually works.
This is my current understanding -- did I get anything very wrong? Or maybe very right?
To get positioning info, there are several sources:

* LLOYDS. They are pricey; they have an extensive network of AIS receivers, and have very accurate positions. They are meant to be the most accurate

* AISHUB. They seem to be the "open source" equivalent of AIS data: to get the data, you must join the network and share your feed. This way, the network grows and everybody wins.

* Marinetraffic.com. It seems to be the same as AISHUB, but run by a company with their own network of receivers. (Is this correct...? Or do they piggyback from AISHUB...?)

* Vesselfinder.com. They admit they use AISHUB (www.vesselfinder.com/faq)

I assume a LOT Of other sites are the same as vesselfinder.com -- they all use AISHUB (I assume they put up a station, and get access to the feed!)

Is this a semi-comprehensive view of how where AIS data comes from? Are there more sources?

Merc.

Hey Trek, so as I understand the system, it's taking a vessels position, course, speed etc using gps onboard, but it's relaying that data (along with static info like the vessel name, size, etc) entirely via VHF, either to any vessel within VHF range and any shore based VHF stations within VHF range. No other satellite communication is used beyond the onboard gps positioning going on, that is to say the AIS data from individual vessels isn't uploaded to a sattelite. It's the shore based VHF stations that relay the data to various organizations web servers for display on the likes of Marine Traffice etc. Is that correct? Or do the class A transponders on commercial vessels upload directly to satellite as well?

There are satellite receivers, but mostly it is shore and vessel based.
For a detailed explanation see here.
en.wikipedia.org/wiki/Automatic_identification_system