Automatic Identification System

The Automatic Identification System (AIS) is a shipborne tracking and communication system that automatically exchanges a vessel's identity, position and movement data. It allows ships and shore authorities to see and track participating vessels, thereby improving navigation safety and broader maritime domain awareness.

How vessel tracking works

An AIS transponder uses VHF radio to exchange information with nearby equipped ships and shore stations. Satellite receivers can extend tracking beyond coastal reception.

• Static and voyage data identify the vessel, including its name, unique maritime identity, type and destination.
• Dynamic data from navigational sensors report position, course and speed at regular intervals.
• Received data can be displayed with electronic charts or radar information, creating a continuously updated local traffic picture.

How it improves maritime safety

By revealing a vessel's identity and movement, AIS strengthens situational awareness for both mariners and coastal authorities.

• Ships can identify approaching traffic and assess collision risk, especially at night, in congested waters or during poor visibility.
• Vessel Traffic Services can monitor traffic, manage port approaches and warn ships about developing hazards.
• Search and rescue agencies can use the transmitted identity and last reported movement to locate and assist vessels in distress.
• Aggregated tracking supports maritime domain awareness by revealing traffic patterns and unusual vessel behaviour.

International framework and limitations

Carriage requirements arise from SOLAS Chapter V, Regulation 19. They generally cover ships of 300 gross tonnage and above on international voyages, cargo ships of 500 gross tonnage and above on other voyages, and passenger ships irrespective of size.

• AIS supplements, but does not replace, radar, visual lookout, safe navigation practices or compliance with collision regulations.
• Coverage and reliability may be reduced when equipment is switched off, signals are obstructed, or incorrect or manipulated data are transmitted.
• These limitations make complementary radar, satellite and other data important for initiatives such as the Quad's Indo-Pacific Partnership for Maritime Domain Awareness.