The shipborne Automatic Identification System (AIS) as specified by IMO, is a ship and shore based broadcast system, operating in the VHF maritime band. It is capable of sending and receiving ship information such as identity, position, course, speed, ship particulars and cargo information to and from other ships, suitably equipped aircraft and shore. It can handle over 2,000 reports per minute and updates information as often as every two seconds. It uses Self- Organising Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure stable and reliable ship-to-ship and ship-to-shore operation.

When used with an appropriate graphical display, shipboard AIS enables the provision of fast, automatic and accurate information regarding risk of collision by calculating Closest Point of Approach (CPA) and Time to Closest Point of Approach (TCPA) from the positional information transmitted by target vessels.

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