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What is the Automatic Identification System (AIS)?
Picture a shipboard display system (e.g. radar, ECDIS, chart plotter, etc.) with overlaid electronic chart data that includes a mark for every significant ship within radio range; each as desired with a velocity vector (indicating speed and heading). Each ship "mark" could reflect the actual size of the ship, with position to GPS or differential GPS accuracy.
By "clicking" on a ship mark, you could learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information. Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, could also be available. Display information previously available only to modern Vessel Traffic Service operations centers could now be available to every AIS-equipped ship.
With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you could dial it up directly using GMDSS equipment. Or you could send to the ship, or receive from it, short safety-related email messages.
The AIS [47 CFR 80.5, AIS Definition] is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. Shipboard AIS devices use either Self-Organizing Time Division Multiple Access (SOTDMA) or Carrier-Sense Time Division Multiple Access (CSTDMA) technology.
WHAT AIS BROADCASTS
A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor. It will continue transmitting even if position information is lost. The information broadcast includes