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AIS is a system that ships use to communicate their positions to each other as part of the global maritime safety system. Since required in December 2004, all ships over 300 tons must carry an AIS system which broadcasts information about the ship to any suitably equipped receiver.

AIS uses very short bursts of high speed data on two VHF channels in the marine band. The two frequencies used are 161.975 (Marine ch 87) and 162.025 (ch 88) MHz. Ships broadcast their identity, position, course, speed and destination so that other ships can take account of their movements.