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 About UAIS (AIS)
About the UAIS (AIS) standard
Universal Automatic Identification System
The UAIS (Universal Automatic Identification System), colloquially known as AIS, is a civilian automatic information system which makes possible the exchange of data between ships and between ships and land based stations.
 A ship equipped with AIS continuously transmits information on e.g. the ships’ name, position, course, speed, draught, type of vessel along with data on the ships' cargo etc. The information is transmitted via radio communication to other ships equipped with AIS as well as to land based AIS-stations.
Land based AIS-stations can send short messages to AIS-equipped ships in a given area, thus providing shipping traffic with important data on the area concerned. AIS data is presented to the user by means of electronic communication systems that support further data processing, for instance by filtering out unwanted information and so on.
The AIS system is based on the following main principles:
- Sending out information on your own vessel to other ships and coastal stations
- Receiving information from other ships and coastal stations
- The use of an independent organizational method of transmission
- A new concept (cellular concept) for efficient utilization of frequencies
- SOTDMA – Self Organized Time Division Multiple Access
It is assessed that AIS can contribute significantly in identifying and positioning shipping traffic, thus playing an important role in outlining the maritime situation as a basis for traffic and marine environment surveillance. Furthermore, the accurate navigational statistics provided by AIS facilitate identifying potential danger areas, areas in which navigational regulation such as traffic separation schemes or compulsory pilotage can be applied.
 In narrow waters, where there is a bend, it may be difficult for two ships to 'see' each other - visually or by radar, and even in rare cases with AIS - due to the shadowing effects of the surrounding terrain on radio signals. If such waters are trafficked by large vessels, this problem can be solved by setting up a repeater station at a suitable position to repeat the ships’ AIS transmissions.
With the AIS system it is possible - if necessary by the means of a repeater station - to enable ships in a narrow passage to 'see' each other, even though surrounding terrain blocks the view - visually or by radar.
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