Unlike AIS, the Thales transponders also give the port operators complete control over the system. They can vary the reporting intervals and content of their transponder signals or remove a target from a crowded display if necessary. They can also set up guard zones to trigger alarms if a harbour vessel crosses a designated line.

The transponder networks at Shannon and Waterford are also used to transmit the track table data from distant radar stations back to the VTS without cost, eliminating the need for expensive telephone or microwave links between each radar station and the control headquarters. Radar data is also transmitted to all other TDMA units in the region so the full VTS image can be seen wherever a radar display is linked to a TDMA receiver.

The system can also be used to distribute differential GPS corrections, tide gauge and wind speed data around the network.

Because strong currents at the entrance to the Shannon can occasionally move buoys, TDMA transponders aboard the pilot launches have also proved a reliable and convenient way of checking their position with survey grade DGPS accuracy.

Two ferries that cross the River Shannon between Tarbert and Killimer have also been fitted with TDMA transponders. They work around a blind headland that makes them invisible to radar but it has no effect upon TDMA communications. They remain visible to port controllers who can provide guidance to approaching shipping while benefiting from a major advance in operational safety and efficiency.

MJ Information No: 18048