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Y1-03-0222 Rev. C
SECTION 1 - WHAT IS AIS?
1. Overview
AIS is an acronym for Automatic Identification System. AIS increases navigational safety and collision
avoidance by transmitting vessel identification, helping to reduce the difficulty of identifying ships when not in
sight (e.g. at night, in radar blind arcs or shadows or at distance) by broadcasting navigational intentions to other
vessels by providing ID, position, course, speed and other ship data with all other nearby ships and land based
stations.
According to International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA)
regulations, AIS is defined as follows:
AIS is a broadcast transponder system, operating in the VHF maritime mobile band. It is capable of sending ship
information such as identification, position course, speed and more, to other ships and to shore. It can handle
multiple reports at rapid update rates and uses Carrier Sense Time Division Multiple Access (CSTDMA)
technology to meet these high broadcast rates and ensure reliable and robust ship to ship operation.
The International Maritime Organization (IMO) defines the performance standards as follows:
Ship to ship working, ship to shore working, including long range application, automatic and continuous
operation, provision of information messaging via PC and utilization of maritime VHF channels
The Modules: GPS system, AIS Transponder, VHF Antenna, and the Data Power Cable (appropriate application
software connects the individual modules).
AIS are required to function flawlessly in a variety of modes. The regulations require that the system be capable
of:
An "autonomous and continuous" mode for operation in all areas. This mode shall be capable of
being switched to/from one of the following alternate modes by a competent authority;
An "assigned" mode for operation in an area subject to a competent authority responsible for traffic
monitoring such that the data transmission interval and/or time slots may be set remotely by that
authority;
A "polling or controlled" mode, where the data transfer occurs in response to interrogation from a ship
or competent authority.
This illustration depicts a typical AIS System, where two or more AIS equipped vessels (and shore based
systems) are automatically communicating with each other.