How does the COSPAS-SARSAT satellite system determine the position of a ship in distress?

The COSPAS-SARSAT satellite system determines the position of a ship in distress primarily by measuring the Doppler shift of the 406 MHz signal transmitted by the distress beacon. When the beacon transmits a signal, the satellite receives this signal and detects changes in the frequency caused by the relative motion between the satellite and the beacon due to the Doppler effect. By analyzing these frequency shifts, the system can calculate the velocity of the beacon and derive its position accurately.

This method is reliable and effective, as it allows for real-time tracking and position determination without needing direct visual contact or ground-based triangulation. The system can perform this processing quickly as it operates in low Earth orbit, providing timely information for search and rescue operations.

The other methods listed would not provide the same level of immediate response or accuracy. For instance, using GPS coordinates would rely on the ship having a functioning GPS receiver and being able to transmit that information, which may not always be feasible in a distress situation. Ground station triangulation typically requires multiple stations receiving signals concurrently, making it less effective than Doppler-based positioning in many scenarios. Finally, visual identification is not practical in maritime distress situations, where conditions can vary greatly and visibility may be limited.