AIS is an English abbreviation for automatic identification system. The AIS is a digital communications system that allows ships, shore and other stations to exchange position and other information automatically. There are two categories of AIS: class A and class B. SOLAS vessels are obliged to carry a class A device, while class B is usually used on boats or yachts.
The AIS is designed to enhance the safe navigation of vessels and to provide safety and security information to relevant authorities. It allows vessel identification, assists in target tracking and simplifies information exchange. It is sometimes found aboard non-SOLAS craft, and can be used by shore stations (such as VTS centers), aircraft and aids to navigation.
The AIS is basically a VHF radio communication system operating on marine-band frequencies. Its range is similar to that of VHF radios. A vessel's dynamic data (position, speed over ground and course over ground) is taken from the GPS. The AIS class B operates at 2 watts and may offer less range than class A devices. The majority of class B AIS devices are expected to use a basic transmission mode (TDMA).
Class B AIS is less expensive than class A; they operate at a lower power level, limited to less than 2 watts, compared to the 12.5 watts of class A. Class B devices have a slow, twice-per-minute update rate, given the maneuverability and speed of small craft and the update rates of radar. Class A AIS units update more rapidly. The location of the AIS antenna can affect range.
