Which method of communication is primarily used for distress alerts in GMDSS?

The method of communication primarily used for distress alerts in the Global Maritime Distress and Safety System (GMDSS) is Digital Selective Calling (DSC). DSC is an advanced communication technique that automatically sends distress alerts to all ships in the vicinity and relevant shore stations, providing a quick and reliable way to communicate emergencies on the sea.

When a vessel is in distress, using DSC allows the operator to send a distress message at the push of a button, which includes important information like the vessel's identity, its position, and the nature of the distress. This greatly enhances the chances of a swift response and increases safety at sea.

DSC is designed to work over VHF, HF, and MF radio frequencies, providing wide coverage and ensuring that distress messages can be sent even in challenging conditions. While VHF radio can be utilized for distress communication, it does not have the same level of automation and efficiency as DSC, making it less effective for rapidly alerting others in an emergency. Visual signals and satellite phones also serve important roles in maritime communication but are not the primary means specified for distress alerts within the GMDSS framework.