The COSPAS/SARSAT satellite system is a joint programme, co-ordinated by the USA, Canada, France and Russia, using polar orbiting USA and Russian satellites. Many countries participate with ground facilities known as Local User Terminals (LUTs) to provide a global search and rescue service. Previously, EPIRB detection depended on overflying aircraft which listen on the international aviation and military distress frequencies, to report any signals they heard. Today, an EPIRB can be detected and located within a few hours of activation, even in an area remote from air routes.

An activated EPIRB is located using an effect known as Doppler shift. Due to the relative motion between the satellite and the EPIRB, the EPIRB's transmitter frequency appears to change (much like the pitch of the whistle on an approaching train changes) . The signal variations are re-transmitted to an LUT and then to a Marine Rescue Co-ordination Center (MRCC), where computers automatically analyse the Doppler shifts and calculate the EPIRB's location by relating it to the satellites precisely know position in orbit. The EPIRB's position can generally be calculated to within 20 kms. From there, rescue vessels or aircraft are despatched with tracking equipment to quickly home in on the beacons signal.

Local User terminals (LUTs) are now located stategically throughout most of the world. In Oceania, LUTs are operational in Bundaberg (Queensland), Albany (Western Australia), Wellington (New Zealand), Indonesia and Singapore.

The diagram depicts the typical coverage area and average time to detection of a 121.5 MHz EPIRB by the Australian and New Zealand LUTs using the COSPAS / SARSAT system.

COSPAS-SARSAT CHANGES

COSPAS-SARSAT is the international organisation that operates a series of satellites in low altitude and geostationary orbits for search and rescue. The Council of COSPAS-SARSAT announced in 2000 that it would be phasing out satellite processing of emergency beacons operating in the 121.5/243 MHz range and encouraging users to adopt 406 MHz beacons.

Why the change?

Older 121.5 MHz system required that a satellite be in view of both the beacon AND the land based LUT (Local User Terminal) before activation could be reported (the satellite acted as a relay for the beacon's signal). This limited the useful detection range to areas immediately surrounding countries which supported LUT's, leaving more isolated areas (such as the antarctic) unprotected.

406 MHz beacons transmit a digital message which can be stored on the satellite, then re-transmitted to the next LUT that comes into view. This provides true global coverage. In addition, the digital message is able to provide encoded information about the vessel and its owner. The use of 406 MHz distress beacons will therefore minimise the problems with false alerts being received by rescue coordination centres around the world.

A CAUTIONARY NOTE

The satellite compatible EPIRB is the most significant advance in search and rescue technology for many years. It is not of course, a substitute for a marine radio. Mariners should not be over-reliant on any single system. Wise and safe mariners plan carefully, ensure that shore contacts know their sail plan, carry a marine radio and the correct range of other safety equipment and operate their craft sensibly to suit conditions at sea.

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The satellite compatible EPIRB is the most significant advance in search and rescue technology for many years. It is not of course, a substitute for a marine radio. Mariners should not be over-reliant on any single system. Wise and safe mariners plan carefully, ensure that shore contacts know their sail plan, carry a marine radio and the correct range of other safety equipment and operate their craft sensibly to suit conditions at sea.