AIS (Automatic Identification System) is a system that makes it possible for a vessel to identify and track the movements of other vessels. The system was developed and implemented to provide access to more information about vessels in the area than can be obtained via radar. For instance, AIS shows the identity and size of vessels – even those that are in radar shadow, behind islands, etc.
AIS uses two VHF radio channels. The information is transmitted in short “data packets” at clearly defined and synchronised intervals. The information consists of the vessel’s identity, position, course, speed, heading, etc., and is transmitted at intervals of 2-10 seconds, depending on the vessel’s speed and maneuvers. Information about the vessel’s size, type of cargo and destination is sent at longer intervals. Position, course and speed are retrieved from the same system used for vessel navigation, usually a GPS/DGPS receiver. All vessels within VHF range can receive information via their own AIS equipment. The information is also received on land through the Swedish Maritime Administration’s network of AIS base stations.
The information may be displayed in various ways. The minimum requirement onboard is a text display where information about the vessels nearest yours is presented with ID, distance and bearing. To get full use out of the information, a graphical display should be used where the AIS information is displayed either integrated with radar information or on an electronic chart display, preferably ECDIS.
AIS equipment onboard works continually and in normal operation autonomously, without requiring any action from the operator. The system is self-organising, that is, the vessel’s AIS equipment considers the information transmitted from surrounding vessels to select appropriate transmission times without any central control. As a result, no fixed infrastructure or command centre is required for the system to work and exchange information between vessels.
The Swedish Maritime Administration was involved in the development of AIS standards and promoted the mandatory use of AIS. The United Nations International Maritime Organization (IMO) resolved in 2001 that all vessels that comply with the SOLAS Convention and are larger than 300 tonnes shall have AIS onboard. The requirement took force on 1 July 2002 for new vessels and an implementation schedule applies to pre-existing vessels. All vessels in international traffic have been equipped with AIS since 31 December 2004 and vessels in national operation must be equipped with AIS by 1 July 2007. The requirement applies to all passenger ships, regardless of size.
The Swedish Maritime Administration has a network of land-based AIS base stations to receive AIS information from vessels and transmit safety-related information. AIS information is used for purposes including improving maritime safety information, maritime search and rescue missions and icebreaking operations.
The information is available in various departments of the Swedish Maritime Administration and to other government agencies through a computer network.
AIS data from all countries in the Baltic region is collected, aggregated and redistributed for surveillance purposes to different organizations in the HELCOM-countries. The data is also stored centally to facilitate production of reliable statistics of the ship traffic in the Baltic. AIS data is also exchanged with other EU member states, via the “Safe Sea Net” system.