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SARSAT

SARSAT. COSPAS-SARSAT. Cospas COsmicheskaya Systyema Poiska Aariynyich Sudov which translates loosely into “Space System for the Search of Vessels in Distress” Sarsat Search and Rescue Satellite Aided Tracking

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SARSAT

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  1. SARSAT

  2. COSPAS-SARSAT Cospas COsmicheskaya Systyema Poiska Aariynyich Sudov which translates loosely into “Space System for the Search of Vessels in Distress” Sarsat Search and Rescue Satellite Aided Tracking Cospas-Sarsat provides, free-of-charge, distress alert and location information to search and rescue authorities anywhere in the world for maritime, aviation and land users in distress.

  3. SARSAT System Operation GEO Satellites LEO Satellites Local User Terminal Rescue Coordination Center Mission Control Center Emergency Beacons

  4. LEO and GEO Satellites Two types of satellites: Low-earth orbiting (LEO)/polar orbiting (LEOSAR); and Geosynchronous earth orbiting (GEO or GEOSAR) – 406 MHz only

  5. Local User Terminals 39 LEOLUT Sites

  6. Local User Terminals 6 GEOLUTs

  7. LEO and GEO SAR Satellites • Geosynchronous Earth Orbiting (406 MHz only) • Large ‘footprint’ – sees almost ½ of the Earth • Holds position over the equator at a fixed longitude • At about 23,000 miles altitude, its orbital speed exactly matches the speed of the Earth’s rotation • Low Earth Orbiting (121.5 MHz and 406 MHz) • Smaller ‘footprint’– sees smaller area • Lower than GEO – at about 530 miles altitude • Moves over surface of Earth • Orbital period about 100 minutes • Orbit traces a sine-wave over a map • Moves in a circle roughly crossing the North and South poles • The Earth rotates underneath, so it covers a different area on each orbit

  8. SARSAT: A Snapshot in Time

  9. SARSAT: A 3D Look

  10. LEO and GEO Satellites Typical Satellite Footprints GEO Footprint LEO Footprint

  11. Doppler Position From LEO Satellites121.5 MHz Local Coverage – 406 MHz Global Coverage Satellite 406 MHz beacon detections can be stored on board the satellite and re-broadcast later LUT 121.5/243 MHz Beacon Detection of a 121.5/243 MHz beacon requires mutual visibility between beacon, satellite and ground station (LUT) Satellite LUT 406 MHz Beacon

  12. Doppler Shift Position Solution • As a LEO satellite passes abeam the signal, the received radio frequency shifts • Analogous to sound frequency shift of passing train or car • Sharpness of frequency shift can be used to determine distance away from satellite’s ground track

  13. Satellite “footprint” Limit of satellite visibility (this pass) Observed frequency time Doppler Shift Position Solution

  14. Two equidistant candidate position solutions – these are called “elementals” Doppler Shift Position Solution • Doppler shift on 121.5 MHz provides two candidate positions • A second satellite pass is needed to determine which is the correct one Satellite Ground Track Satellite location at Doppler zero shift Perpendicular at Doppler zero shift

  15. Doppler Shift Position Solution • Doppler shift on 121.5 MHz provides two candidate positions • A second satellite pass is needed to determine which is the correct one 2nd Satellite location at Doppler zero shift Position that agrees with 1st satellite – this is called a “merge”

  16. Understanding “merges” • Each successive merge is cumulative (i.e. all elementals that appear to be the same target are averaged together)

  17. Doppler Shift Position Solution • On 406 MHz, the stronger, higher quality signal permits using the Doppler shift component of the Earth’s rotation to determine which side of the satellite the signal is on • Thus, 95% of the time, only one satellite pass is needed

  18. Variations and Capabilities • 121.5 MHz – Usual for ELTs and EPIRBs • Low power, continuous analog broadcast • Must be ‘heard’ by satellite for at least 4 minutes to generate a location solution • SARSAT Location is within 11NM (90% accuracy) • 48 Hour nominal battery life • 243 MHz – Used by Military • Characteristics similar to 121.5 ELTs • Received only by US satellites • Increases time between passes

  19. Variations and Capabilities • 406 MHz – New ELT frequency • Digital data burst with UIC – Unique Identification Code • Satellite must ‘hear’ 3 bursts (about 3 minutes) to generate a location solution • Most include a 121.5 transmitter to allow searchers to hear and locate the signal • Data burst information is stored on board satellites until it can be downloaded to a LUT; provides global coverage • Geosyncronous satellites also monitor for instantaneous alert • Optional GPS data • 5 Watts power

  20. Variations and Capabilities • 406 MHz – New ELT frequency (cont.) • Unique Identification Code • Requires owner registration • Database associates UIC with vessel or aircraft and its owner • Allows most false alarms to be resolved with a phone call • Eliminates non-beacon false alarms • Stronger, higher quality signal for satellite reception and position determination

  21. Problems with 121.5 MHz Alerting • Number of False Alerts • Timeliness • Accuracy • Identification • Reliability/Operation

  22. Problems with 121.5 MHz Alerting • Number of False Alerts • Approximately 120,000 alerts sent to United States RCCs annually • 75% of the alerts originate from non-beacon sources • Only a few hundred real distress alerts annually • False alert rate (for all alerts, beacon and non-beacon, sent to RCCs) over 99%

  23. Problems with 121.5 MHz Alerting • Timeliness • Due to the number of false alerts and the inability to resolve ambiguity on the first pass, RCCs usually have to wait for the second or third satellite pass before responding. • This delays search and rescue efforts by up to two hours or more • The response can be further delayed because the 121.5 MHz system requires mutual visibility

  24. Problems with 121.5 MHz Alerting Accuracy Generally between 7 - 12 miles. Corresponding search area approximately 450 square miles Identification Lack of beacon identification means that resources have to be expended in order to determine the source - real alert, false alert or interferer

  25. Problems with 121.5 MHz Alerting • Reliability/Operation • Lower power transmitters (50 - 100 mw) are not designed to be detected by satellite • Interference in 121.5 MHz band can prevent signals from being detected by satellite

  26. A Typical Day at AFRCC

  27. End of 121.5 MHz Satellite Processing • The termination of 121.5 MHz satellite alerting refers to the cessation of satellite processing of 121.5 MHz signals • It does not mean the elimination of the use of the frequency or the use of 121.5 MHz emergency beacons • 406 MHz EPIRBs and ELTs will continue to have a low power 121.5 MHz transmitter for homing purposes • 243 MHz satellite processing will also be terminated

  28. Variations and Capabilities Recap: 121.5/243 MHz vs. 406 MHz

  29. SARSATFor More Information… • http://www.sarsat.noaa.gov/ • http://www.cospas-sarsat.org/ • http://www.uscg.mil/hq/g-o/g-opr/sar.htm • http://www.acc.af.mil/afrcc/ • http://poes.gsfc.nasa.gov/sar/sar.htm

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