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Operational Sea Areas
The GMDSS is based on the concept of using four sea areas
to determine the operational, maintenance and personnel requirements
for maritime radiocommunications, viz:
| Sea Area A1 |
A coastal area within radiotelephone coverage of at least
one VHF coast station in which continuous DSC alerting
is available. Such an area could extend typically 30-50
nautical miles from the coast station. |
| Sea Area A2 |
An area, excluding sea area A1, within the radiotelephone
coverage of at least one MF coast station in which continuous
DSC alerting is available. This area typically extends
to up to 50-150 nautical miles offshore. |
| Sea Area A3 |
An area, excluding sea areas A1 and A2, within the coverage
of an Inmarsat geostationary satellite in which continuous
alerting is available. This area lies between about latitudes
70º North and South. |
| Sea Area A4 |
An area outside sea areas A1, A2 and A3. This is essentially the polar regions, north and south of the 70º of latitude. |
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Operational Details
The worldwide communication coverage of the GMDSS is
achieved by a combination of satellite (Inmarsat) and terrestrial
systems. Based on the range limitations of each system the
four areas have been defined accordingly to the coverage
of VHF,MF,HF Coast Radio Services and Inmarsat services.
The type of radio equipment required to be carried by a
vessel is therefore determined by its area of operations.
Area Description |
Distance |
Radio |
Frequencies |
EPIRBs |
Survival Craft |
| A1 |
Within range of shore-based VHF stations |
Depends on antenna height at shore-based VHF station, about 30-50 n miles |
VHF |
156.525 MHz (Ch 70) for DSC or156.8 MHz (Ch 16) RT |
Either L-Band (1.6 GHz) or 406 MHz COSPAS-SARSAT or VHF EPIRB (after Feb 1999) |
9 GHz radar transponder (SART); VHF portable radio (Ch 16 and one other frequency) |
| A2 |
Within range of shore-based MF stations |
about 50-150 n miles |
MF
VHF |
as above, plus2187.5 kHz DCS,2182 kHz RT,2174.5 kHz NBDP,518 kHz Navtex |
L-Band (1.6 GHz) or 406 MHz COSPAS-SARSAT |
as above |
| A3 |
Within geo-stationary satellite range (i.e. Inmarsat) |
70°N - 70°S |
HF or Satellite MF VHF |
as above, plus 1.5-1.6 GHz alerting or as A1 and A2 plus
all HF frequencies |
L-Band (1.6 GHz) or 406 MHz COSPAS-SARSAT |
as above |
| A4 |
Other areas (i.e. beyond Inmarsat range) |
North of 70°N or South of 70°S |
HF
MF
VHF |
. |
406 MHz COSPAS-SARSAT |
as above |
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