Automatic Identification System (AIS)
Automatic Identification System (AIS) is a system that ships use to automatically transmit their identity, position, course, speed and destination to each other and to coast stations. This information can be used by other ships to take account of their movements and by coast stations for coastal surveillance and vessel traffic management. Special software can make this information available on a screen or radar plot. AIS is part of the global maritime safety system (GMDSS). As of 31 December 2004, all ships over 300 tons must carry an AIS system which broadcasts information about the ship to any suitably equipped receiver.
The messages that are broadcasted by AIS contain the following information:
Messages containing static information are broadcasted every 6 min or, when data has been amended. Messages containing dynamic information are broadcasted in an interval between 2 s and 3 minutes depending on the speed of the ship and if the course is changing or not.
There are also beacons and light ships equipped with AIS to assist navigation, especially at sea.
AIS uses very short bursts of high speed data on two VHF channels in the maritime band. The two frequencies used are 161.975 (Maritime radio channel 87H) and 162.025 (channel 88H) MHz. The transmision power is 12.5 W. Transmissions can be received up to a distance of about 30 - 40 km.