AIS target more than 2000km away

[MarkJ68]

There are many military platforms that relay AIS tracks via onboard systems. That is likely what you saw.

[GrowleyMonster]

Tropospheric ducting.

[StuM]

Originally Posted by Nicholson58

>...... or a repeater installed by the Coast Guard or an passionate amateur .... ?


I go with this option. Check another day and also contact the CG and relate your observations.

A repeater reporting targets 2000km away across open ocean? Where did the repeater get the data from?

[MarkJ68]

That's exactly what it is. I used to fly P3's. On board AIS relay systems input tracks and rebroadcast, thus widening the AIS footprint. We also have high altitude drones (60+k feet) that do the same thing.

[PiAn]

There is a spot south of Sardinia, where, year after year, I see boats up to Gibraltar - 350Nm away (and south of France, and Lybia - hundreds of targets). Sailing 10 Nm to the north, all disappears and only 20+ closeby targets remain.
Always funny.

[bikesherpa]

In Italy, the Coast Guard operates a single network of 63 land AIS stations. Some of these stations have the "repeater" function enabled. It is therefore common in some areas to receive targets 1000km away.
If you read Italian, you can find more info here
https://www.guardiacostiera.gov.it/m...rkshop-p-m-i-s

[StuM]

Originally Posted by bikesherpa

In Italy, the Coast Guard operates a single network of 63 land AIS stations. Some of these stations have the "repeater" function enabled. It is therefore common in some areas to receive targets 1000km away.
If you read Italian, you can find more info here
https://www.guardiacostiera.gov.it/m...rkshop-p-m-i-s

How far apart are these repeaters? Note that the AIS standard limits the number of repeats to three, so unless they are somehow talking to each other over 300km distances, you won't see a vessel from 1000km away.


From your link, there is nothing there about that network repeating and re-broadcasting AIS signals to ships from long distances. It's a network to collect and centralise the AIS signals in a national HQ.


In fact the highlight below shows that it only repeats local traffic to ships in some areas.



"Directive 2002/59 / CE of 27 June 2002 of the European Parliament and of the Council, concerning the establishment of a community vessel traffic monitoring and information system, the General Command as " National Competent Auth Ority ", provided for the creation of a complex" national network "for receiving the AIS ( Automatic Identification System ) information transmitted by the ships. The network consists of 63 base stations ( base stations ) installed in such a position as to guarantee the complete radioelectric coverage of the national coastal profile with a depth that extends, where possible, to the entire Search and Rescue (SAR) area of ​​Italian competence .
The information acquired is centralized at the General Command and made available by it, through appropriate machine-machine interfaces to other services of responsibility of the General Command and to other State Administrations, thus allowing them to avoid having similar equipment for their own purposes institutional.
In this perspective, the Italian Vessel Traffic Service centers do not have their own AIS stations, but make use of the services guaranteed by the " national AIS network " with significant savings in economic terms.
The national AIS network, in addition to receiving the information transmitted by the ships, also provides for the transmission:

• of messages relating to the main Aids to Navigation - AtoN (nominal range> 15 nautical miles). The list of AtoNs reported by the national AIS network is reported in the publication "Radioservizi per la Navigazione" published by the Hydrographic Institute of the Navy as well as on the AtoN page of this site;
• of messages regarding safety of navigation ( safety );
• base station report messages through which naval units can synchronize their AIS transmissions;
• in certain geographical areas, in repeater mode, the AIS information received in the same area.

[bikesherpa]

I do not know which base stations are inter-connected, but while sailing in the northern Adriatic near Venice I can frequently see ships (class A transmitters) down in the Otranto channel which is 500nm away.