Acting ahead of an International Marine Organization
(IMO) -mandated Automatic
Identification System (AIS), the harbormasters of Cork and
Shannon, Ireland, have implemented Thales Navigation
systems within their STN Atlas VTS installations. By equipping
key harbor craft with Thales Navigation TDMA (Time Division
Multiple Access) transponders, the ports have overcome the
geographical limitations of radar and achieved a dramatic advance
in the efficiency and safety of their operations.
Thales Navigation transponders are similar to AIS, but the Thales
Navigation system includes the major advantage of giving the port
operator complete control over it. AIS transponders are required
to function independently of any control center so that two
ships meeting in mid-ocean can exchange and display information
automatically. The ship's master decides the content of the
display, and no port controller can change it or choose not to
receive its messages. The Thales Navigation TDMA system operates
within a designated area for which there is a central control.
All transponder messages lead to the port controller who has
options unavailable on the AIS system.
With TDMA the port controllers have the freedom to control the
reporting intervals and content of the transponder signals. They
can also set up guard zones that can trigger alarms if a harbor
vessel crosses a demarcation line, and they can remove a target
from the display if crowding makes it desirable.
For ports such as Shannon and Waterford, where the VTS radar
sites are far apart; the TDMA transponder network can transmit
the radar track table data back to the port control. This
eliminates the need for costly tied telephone lines or microwave
data links between each station and the control headquarters.
Because this data is also transmitted to all other TDMA unit
the region, the same complete VTS radar image can be seen by
the Coast Guard, on pilot vessels or wherever a radar display is
linked to a TDMA receiver. The transmission costs of the system
are zero, so the system can also be used to distribute tide gauge
and wind speed data around the network as an additional aid to
pilots and harbor craft. The system automatically transmits
precise differential GPS corrections to all vessels equipped with
a TDMA unit operating within the area.