What is AIS and how does it work?

AIS (Automatic Identification System) is a tracking system used for collision avoidance on sea and monitoring of maritime traffic. Vessels transmit their unique identification, position and voyage information multiple time per minute using AIS transponders on board. These AIS reports can be captured by nearby ships, satellites and by AIS receiver stations (terrestrial) mounted on shore. 

The IMO (International Maritime Organization) decided that all passengers' vessels and all commercial vessels over 299 GT traveling internationally must carry a Class A AIS transponder on board. Smaller vessels can carry a Class B AIS transponder. This standard is binding since December 2004 for all merchant vessels longer than 20 m or with more than 50 passengers on board. Since 2008 for all vessels with more than 500 BRZ. 

A GPS receiver (Global Positioning System) which is included in the AIS transponder on board collects the vessel’s position and movement information. This dynamic information combined with the static information provided by the vessel’s crew are automatically broadcasted via VHF. They send on two frequencies: 

• Class A: 161,975 MHz (AIS1 87B) for merchant ships and all binding vessels.
• Class B: 162,025 MHz (AIS2 88B) for all other vessels like fishing vessels and pleasure crafts.

The AIS data can be received by nearby vessels or AIS receiver stations if they are within reach. Underuse of special software the data can be processed and displayed on chart plotters or computers (e.g. on the FleetMon Explorer). In the case the AIS-data is received by satellites, the terms Sat-AIS, Satellite AIS or S-AIS are used.

Meanwhile the use of AIS information has various purposes and does help people in different work areas, for example: vessel owners/managers/builders, port authorities and harbor masters, ship agents/brokers/charterers, researchers and data analysts, search and rescue teams, coast guard and border patrol, vessels' crew and their families, maritime enthusiasts, ...