The Search and Rescue instruments are part of the international Cospas-Sarsat system designed to detect and locate Emergency Locator Transmitters (ELTs), Emergency Position-Indicating Radio Beacons (EPIRBs), and Personal Locator Beacons (PLBs) operating at 121.5, 243, and 406.05 MHz. The NOAA spacecraft carries two instruments to detect these emergency beacons: the Search and Rescue Repeater (SARR) provided by Canada and the Search and Rescue Processor (SARP-2) provided by France. Similar instruments are carried by the Russian COSPAS polar-orbiting satellites.
The SARR transponds the signals of 121.5, 243, and 406.05-MHz emergency beacons. However, these beacon signals are detected on the ground only when the satellite is in view of a ground station known as a Local User Terminal (LUT). The SARP detects the signal only from 406.05-MHz beacons but stores the information for subsequent downlink to a LUT. Thus, global detection of 406.05-MHz emergency beacons is provided. This processor consists of a receiver power unit (rpu) and signal processing unit (spu).
The U.S. fishing fleet is required to carry 406.05-MHz emergency beacons. The 406.05-MHz beacons are also carried on most large international ships, some aircraft, and pleasure vessels, as well as on terrestrial carriers. The 121.5-MHz and 243-MHz beacons are required on many small aircraft with a smaller number carried on maritime vessels.