14 st / March 2017 www.sea-technology.com
major ports and harbors. These linked up to the internet,
encouraging the development of third-party vessel tracking
platforms that allowed anyone with a Web browser to view
all commercial vessels within range. The big breakthrough
around 15 years ago was the unexpected discovery that AIS
signals could be picked up by low-orbit satellites at ranges
10 times greater than at sea level. This marked the dawn of
near-global AIS coverage. As satellite operators continued
to add compact AIS packages to their platforms it became
easier to track vessels even in midocean, and so AIS came of
age as a vessel tracking system whose basic service could be
adapted for a wide range of purposes and users.
Of course, AIS is not the only, or indeed rst, satellite
tracking system. A wide range of maritime satellite-based
A
IS has come a long way in the two decades since it be-
came an indispensable feature of maritime life. Its origi-
nal purpose, which is still an important part of its functional-
ity today, was as a ship-to-ship collision avoidance system.
This it achieves by using VHF signals to continuously transmit
a ship's GPS position, which can then be received by other
vessels within range using AIS transponders and displayed
on electronic charting systems. Associated software can then
analyze the distance, course and speed to ascertain if there is
any risk. Additional information regarding each vessel's iden-
tity, speci cations, cargo and routing can also be packaged
within the VHF signal.
Over time, a network of shore stations, both profession-
al and amateur, developed around the world, starting with
AIS Essential for
Fleet Management, Security
Satellite Tracking Goes Well Beyond Collision Avoidance
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