Introduction to AIS
98-135323-H Chapter 1: Introduction 3
If a vessel operating in a mandatory ship reporting system does switch off its
AIS, this should be reported to the relevant authority. Note that some data is
entered or updated manually, meaning that there is potential for false entry and
for the entered data to become out of date. This includes data related to static
information (e.g. ship identity, dimension) and voyage related data (e.g.
navigational status).
AIS and radar
A difference between AIS and radar is that AIS uses an absolute referencing
system to determine the position, whereas radar determines the position by
relative measurements from the vessel or shore base to observed targets. AIS
may be used together with radar information to provide:
• Vessel identification, heading, course over ground (COG) and speed over
ground (SOG)
• Improved vessel tracking (no target swap)
• Wider geographical coverage
• Greater positional accuracy, dependent on the position input sensor
• Information in radar shadow area ('sees' around bends and behind islands)
• Maneuver data in nearly real time
• No loss of targets in sea, rain and snow clutter
AIS classes
AIS is not only used on board ships. It can be grouped by 'class' (shipborne) and
function. A Ship borne AIS device which contributes by most of the flow of AIS
information, is classified as either Class A, B or Inland AIS. The AIS Class A
stations are ship borne units which meet IMO performance standards and are
required on most commercial ships by the International Maritime organization
(IMO). The SAILOR 6282 AIS Transponder is a combined Class A and Inland AIS
station.
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