seaarea

Sea area is a classification used in maritime radio communications to indicate the type of radio coverage available for distress and safety communications under the Global Maritime Distress and Safety System (GMDSS). The system defines four sea areas—A1, A2, A3, and A4—based on the reach of radio networks from shore stations and satellites. These categories help determine the equipment and procedures ships must use for transmitting distress signals and safety information.

Sea Area A1 covers regions where ships can communicate with nearby coast-based VHF stations, typically within line-of-sight. In A1, distress and safety messages are handled through VHF channels with continuous watch by coastal facilities. Sea Area A2 extends beyond the VHF range but remains within the reach of MF/HF coast stations, enabling longer-distance communications as part of the GMDSS. Sea Area A3 includes most of the world’s oceans where no coast stations are reachable and relies primarily on satellite communication networks (such as INMARSAT) to deliver distress and safety messages. Sea Area A4 comprises polar regions and other areas not covered by A1–A3, where satellite coverage may be limited or unavailable and alternative procedures apply.

These sea-area definitions influence the required equipment on ships, including VHF and MF/HF radios, satellite communication terminals, distress alert systems, and related safety services such as NAVTEX and satellite weather data. The sea-area framework is part of SOLAS regulations and ITU guidelines, guiding search-and-rescue coordination, message handling, and general mariner safety practices.