User's Manual

Introduction
Page 9
2Introduction
2.1 About AIS
The marine Automatic Identification System (AIS) is a location and vessel information reporting system. It
allows vessels equipped with AIS to automatically and dynamically share and regularly update their position,
speed, course and other information such as vessel identity with similarly equipped vessels. Position is derived
from the Global Positioning System (GPS) and communication between vessels is by Very High Frequency
(VHF) digital transmissions.
There are a number of types of AIS device as follows:
● Class
A transceivers. The
se are designed to be fitted to commercial vessels such as cargo ships
and large passenger vessels. Class A transceivers transmit at a higher VHF signal power than class
B transceivers and therefore can be received by more distant vessels, and also transmit more
frequently. Class A transceivers are mandatory on all vessels over 300 gross tonnes on international
voyages and certain types of passenger vessels under the SOLAS mandate.
● Inland A
IS stations.
Similar to class A transceivers with additional features for use on Inland
waterways.
● Class B transceivers. Similar to Class A transceivers in man
y ways, but are normally lower cost due
to the less stringent performance requirements. Class B transceivers transmit at a lower power and at
a lower reporting rate than Class A transceivers.
● AIS base st
ations. AIS base stations are used by Vessel Traffic Systems to monitor and control the
transmissions of AIS transceivers.
● Aids to Navigation (AtoN) transceivers. AtoNs are tran
sceivers mounted on buoys or other
hazards to shipping which transmit details of their location to the surrounding vessels.
● AIS receivers. AIS receiver
s receive transmissions from Class A transceivers, Class B transceivers,
AtoNs and AIS base stations but do not transmit any information about the vessel on which they are
installed.
The AIS950 transceiver is a combined Class A transceiver.
Figure 1 The AIS network