Coverage areas

GMDSS uses 4 coverage areas: A1, A2, A3 and A4.
These areas together cover the sea areas of the world. Sea Area A1 is an area within Very High Frequency (VHF) range of a coast station fitted with Digital Selective Calling (DSC).
This range is about 30 to 40 miles.
Sea Area A2 is an area with Medium Frequency (MF) range of a coast station fitted with DSC. This range is about 150 miles.
Sea Area A3 is an area covered by the Inmarsat Satellite System, excluding Sea Areas A1 and A2.
Sea Area A4 is basically the polar regions that are not covered by the other Sea Areas.