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1st3001001 EN 1_14.docx
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1
WHAT IS AIS?
AIS stands 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 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 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 relevant regulations
requirements:
The system shall 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.
