automatic identification system

A U.S. Coast Guard Operations Specialist using AIS and radar to manage vessel traffic. An AIS-equipped system on board a ship presents the bearing and distance of nearby vessels in a radar-like display format. A graphical display of AIS data on board a ship.

The automatic identification system (AIS) is an automatic tracking system that uses transponders on ships and is used by vessel traffic services (VTS). Originally designed as a terrestrial communication system (ship to ship; ship to shore), satellites are now also used to passively capture the signal traffic. With a few exceptions, AIS traffic is in the form of continual status announcements of a sender to all interested parties in its proximity. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport, since AIS requires relies on accuracy of information transmitted by other vessels, whereas radar independently detect objects. Although technically and operationally distinct, AIS is analogous to the ADS-B system which performs a similar function for aircraft.