Larry, true, this is one method of transmitting AIS data for floating objects. As far as buoys are concerned, AIS provides the possibility to allow them to transmit themselves or remotely from a basestation. Self-transmitting is normally used when environmental data is also transmitted.

I quote from the AIS specifications:
"There are three categories of Aids to Navigation in the AIS system:

Real AtoN: The AtoN is equipped with an AIS Station designed to generate
the appropriate AIS messages using local data from the aid and transmitting it via VHF.

Synthetic AtoN: The AIS message for the AtoN is transmitted from another
location (normally a base station) and the AtoN is physically located at the position given in the
AIS message.

Virtual AtoN:The AIS message is an aids to navigation message but no real aid exists at
the location indicated in the AIS message.


Holger