|What Is COSPAS-SARSAT?|
A COSPAS-SARSAT System Overview
(The graphic below and portions of the text on this page courtesy of NASA and NOAA)
COSPAS-SARSAT is an international, humanitarian satellite-based search and rescue system that has helped save over 20,000 lives worldwide since its inception in 1982 (total as of June 2005).
SARSAT is an acronym for Search and Rescue Satellite-Aided Tracking. COSPAS is an acronym for the Russian words "Cosmicheskaya Sistyema Poiska Avariynich Sudov," which mean "Space System for the Search of Vessels in Distress," indicative of the maritime origins of this distress alerting system.
The system, which operates 24 hours a day, 365 days a year, detects and locates transmissions from emergency beacons carried by ships, aircraft, and individuals. Use of the COSPAS-SARSAT system is FREE to the beacon operator.
Sponsored by Canada, France, Russia, and the United States, the system aims to reduce the time required to alert rescue authorities whenever a distress situation occurs. The rapid detection and location of a downed aircraft, a ship, or an individual in distress are of paramount importance to survivors and to rescue personnel.
The COSPAS-SARSAT system consists of emergency radio beacons (distress beacons), equipment on satellites in low-Earth polar or in geosynchronous orbits, ground receiving stations also called Local User Terminals (LUTs), Mission Control Centers (MCCs), and Rescue Coordination Centers (RCCs).
There are three types of emergency beacons: 1) Emergency Position Indicating Radio Beacons (EPIRBs) for maritime applications, 2) Emergency Locator Transmitters (ELTs) for aviation applications, and 3) Personal Locator Beacons (PLBs) for individuals in distress. Emergency beacons may transmit on 121.5, 243.0 (military) and 406 MHz. Satellite notification of 121.5 MHz alerts are being phased out in the near future 406 MHz has become the international standard providing far better accuracy and fewer false alert search initiations.
Beacons that transmit on 406 MHz send digitally encoded information which includes a beacon I.D. for accessing a user registration database. This database can supply the beacon type, its country of origin, and the registration number of the maritime vessel or aircraft and can also include location data derived from the Global Positioning System (GPS). Encoded location is of great value when using a geostationary (GEO) satellite for relaying beacon signals because a GEO satellite provides immediate alerting.
Emergency contacts provided in the registration allow the RCC to confirm the validity of the alert and may also improive emergency forces response.
The system uses two different types of satellites: polar-orbiting satellites in low-Earth orbit (LEO) and satellites in geosynchronous orbit. Russia and the United States provide the LEO satellite platforms. Canada, France, Russia, and the United States contribute components. The Russian NADEZHDA navigation satellites carry the COSPAS repeater packages, and NOAA weather satellites carry Sarsat packages. The NOAA LEO satellites orbit the Earth every 100 minutes. COSPAS satellites complete an orbit every 105 minutes.
GEO satellites continually view large areas of the Earth from approximately 70 degrees North to 70 degrees South latitudes and can provide immediate alerting and identification of 406 MHz beacons. GEO satellites are operated by the United States, India and the European Union
Even though GEO satellites cannot determine a beacon's location using Doppler processing, the near instantaneous alerting (3 - 5 minutes) with the user I.D., and detective work by the RCC often yield the location of the distress call. Based on this information alone, search planning can begin. Ideally, a SARSAT or COSPAS LEO satellite will overfly the beacon within the next hour and confim with a Doppler-determined location.
Doppler via the LEO satellites provides a location within 2 miles. If the beacon is equipped with GPS or receives a location from onboard navigation equipment, this encoded location is tranmitted to the GEO satellite, providing immediate location information accurate to within 100 meters.
The COSPAS-SARSAT LEO system uses two modes of operation. In the Bent-Pipe or repeater mode, the Search and Rescue Repeater, or SARR, immediately retransmits received beacon signals to any LUT in the satellite's footprint. This mode is possible when the spacecraft is visible to both the beacon and the ground station simultaneously, an area approximately 2,500 miles (4,000 km) in diameter. In the store and forward mode, the on-board processor, or SARP, receives and records search and rescue beacon transmissions and repeatedly retransmits them to LUTs as the satellite orbits the Earth. This mode is possible only with 406 MHz beacons. It provides true global coverage.
The signals received by LEO satellites are relayed to a network of LUTs that locate the beacon by measuring the Doppler shift caused by the motion of the satellite with respect to the beacon. This process can locate beacons within an accuracy of approximately 12.4 miles (20 km) for 121.5 MHz beacons and of approximately 3 miles (5 km) for 406 MHz beacons. (A low-power 121.5 MHz homing signal included in all U.S. 406 MHz beacons helps rescuers determine the final location as they approach, when necessary.)
The location data is then relayed to an MCC that alerts the appropriate RCC or an MCC in another country. If the alert is in an area covered by a foreign MCC, that MCC is alerted, and in turn, notifies its own RCC. The RCC then begins the actual search and rescue operation.
NOAA, the U.S. Coast Guard, and the U.S. Air Force operate the COSPAS-SARSAT system in the United States. NASA provides technical support by investigating system problems and developing technological improvements.More information may be found at: http://www.sarsat.noaa.gov/ and http://poes.gsfc.nasa.gov/sar/sar.htm.
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