SARSAT. COSPAS-SARSAT CospasCOsmicheskaya Systyema Poiska Aariynyich Sudov which translates loosely into “Space System for the Search of Vessels in Distress”

SARSATSARSAT

COSPAS-SARSATCOSPAS-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.

SARSAT System OperationSARSAT System Operation

Local User Terminal

Mission Control Center

Rescue Coordination

Center

LEO Satellites

GEO Satellites

Emergency Beacons

LEO and GEO SatellitesLEO and GEO Satellites

Two types of satellites:

Low-earth orbiting (LEO)/polar orbiting (LEOSAR); and

Geosynchronous earth orbiting (GEO or GEOSAR) – 406 MHz only

Local User TerminalsLocal User Terminals

39 LEOLUT Sites

Local User TerminalsLocal User Terminals

6 GEOLUTs

LEO and GEO SAR SatellitesLEO and GEO SAR Satellites

Geosynchronous Earth Orbiting Geosynchronous Earth Orbiting (406 MHz only)(406 MHz only)

– Large ‘footprint’ – sees almost ½ of the EarthLarge ‘footprint’ – sees almost ½ of the Earth– Holds position over the equator at a fixed longitudeHolds position over the equator at a fixed longitude

» At about 23,000 miles altitude, its orbital speed exactly matches the At about 23,000 miles altitude, its orbital speed exactly matches the speed of the Earth’s rotationspeed of the Earth’s rotation

Low Earth Orbiting Low Earth Orbiting (121.5 MHz and 406 MHz)(121.5 MHz and 406 MHz)

– Smaller ‘footprint’– sees smaller areaSmaller ‘footprint’– sees smaller area» Lower than GEO – at about 530 miles altitudeLower than GEO – at about 530 miles altitude

– Moves over surface of EarthMoves over surface of Earth– Orbital period about 100 minutesOrbital period about 100 minutes– Orbit traces a sine-wave over a mapOrbit traces a sine-wave over a map

» Moves in a circle roughly crossing the North and South polesMoves in a circle roughly crossing the North and South poles» The Earth rotates underneath, so it covers a different area on each orbitThe Earth rotates underneath, so it covers a different area on each orbit

SARSAT: A Snapshot in TimeSARSAT: A Snapshot in Time

SARSAT: A 3D Look

LEO and GEO SatellitesLEO and GEO Satellites

Typical Satellite Footprints

GEO Footprint

LEO Footprint

Doppler Position From LEO SatellitesDoppler Position From LEO Satellites121.5 MHz Local Coverage – 406 MHz Global Coverage121.5 MHz Local Coverage – 406 MHz Global Coverage

121.5/243 MHz Beacon

LUT

Detection of a 121.5/243 MHz beacon requires mutual visibility between beacon, satellite and ground station (LUT)

406 MHz Beacon

Satellite

LUT

406 MHz beacon detections can be stored on board the satellite and re-

broadcast later

Satellite

Doppler Shift Position SolutionDoppler Shift Position Solution

As a LEO satellite passes abeam the signal, As a LEO satellite passes abeam the signal, the received radio frequency shiftsthe received radio frequency shifts– Analogous to sound frequency shift of passing Analogous to sound frequency shift of passing

train or cartrain or car Sharpness of frequency shift can be used to Sharpness of frequency shift can be used to

determine distance away from satellite’s determine distance away from satellite’s ground trackground track


time

Observed frequency

Limit of satellite visibility (this pass)

Satellite “footprint”

Doppler Shift Position SolutionDoppler Shift Position Solution Doppler shift on Doppler shift on

121.5 MHz provides 121.5 MHz provides two candidate two candidate positionspositions

A second satellite A second satellite pass is needed to pass is needed to determine which is determine which is the correct onethe correct one

Satellite location at Doppler zero shift

Two equidistant candidate position solutions – these are called “elementals”

Doppler Shift Position SolutionDoppler Shift Position Solution Doppler shift on Doppler shift on

121.5 MHz provides 121.5 MHz provides two candidate two candidate positionspositions

A second satellite A second satellite pass is needed to pass is needed to determine which is determine which is the correct onethe correct one

2nd Satellite location at Doppler zero shift

Position that agrees with 1st satellite – this is

called a “merge”

Understanding “merges”Understanding “merges”

Each successive merge is cumulative Each successive merge is cumulative (i.e. all elementals that appear to be the (i.e. all elementals that appear to be the same target are averaged together)same target are averaged together)


On 406 MHz, the stronger, higher quality On 406 MHz, the stronger, higher quality signal permits using the Doppler shift signal permits using the Doppler shift component of the Earth’s rotation to component of the Earth’s rotation to determine which side of the satellite the determine which side of the satellite the signal is onsignal is on

Thus, 95% of the time, only one satellite Thus, 95% of the time, only one satellite pass is neededpass is needed

Variations and CapabilitiesVariations and Capabilities 121.5 MHz – Usual for ELTs and EPIRBs121.5 MHz – Usual for ELTs and EPIRBs

– Low power, continuous analog broadcastLow power, continuous analog broadcast– Must be ‘heard’ by satellite for at least 4 Must be ‘heard’ by satellite for at least 4

minutes to generate a location solutionminutes to generate a location solution– SARSAT Location is within 11SARSAT Location is within 11NMNM (90% (90%

accuracy)accuracy)– 48 Hour nominal battery life48 Hour nominal battery life

243 MHz – Used by Military243 MHz – Used by Military– Characteristics similar to 121.5 ELTsCharacteristics similar to 121.5 ELTs– Received only by US satellitesReceived only by US satellites

» Increases time between passesIncreases time between passes

Variations and CapabilitiesVariations and Capabilities 406 MHz – New ELT frequency406 MHz – New ELT frequency

– Digital data burst with UIC – Unique Identification Digital data burst with UIC – Unique Identification CodeCode

– Satellite must ‘hear’ 3 bursts (about 3 minutes) to Satellite must ‘hear’ 3 bursts (about 3 minutes) to generate a location solutiongenerate a location solution

– Most include a 121.5 transmitter to allow searchers to Most include a 121.5 transmitter to allow searchers to hear and locate the signalhear and locate the signal

– Data burst information is stored on board satellites until Data burst information is stored on board satellites until it can be downloaded to a LUT; provides global it can be downloaded to a LUT; provides global coveragecoverage

– Geosyncronous satellites also monitor for instantaneous Geosyncronous satellites also monitor for instantaneous alertalert

– Optional GPS dataOptional GPS data– 5 Watts power5 Watts power

Variations and CapabilitiesVariations and Capabilities 406 MHz – New ELT frequency (cont.)406 MHz – New ELT frequency (cont.)

– Unique Identification CodeUnique Identification Code» Requires owner registrationRequires owner registration

» Database associates UIC with vessel or aircraft and Database associates UIC with vessel or aircraft and its ownerits owner

» Allows most false alarms to be resolved with a Allows most false alarms to be resolved with a phone callphone call

» Eliminates non-beacon false alarmsEliminates non-beacon false alarms

» Stronger, higher quality signal for satellite reception Stronger, higher quality signal for satellite reception and position determinationand position determination

Problems with 121.5 MHz AlertingProblems with 121.5 MHz Alerting

• Number of False Alerts

• Timeliness

• Accuracy

• Identification

• Reliability/Operation


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%


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


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


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

A Typical Day at AFRCCA Typical Day at AFRCC

End of 121.5 MHz Satellite ProcessingEnd 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

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

121.5/243 MHz121.5/243 MHz 406 MHz406 MHz

Doppler Location Accuracy (90%)Doppler Location Accuracy (90%) 11 NM11 NM 3 NM3 NM

Doppler Location (LEO) SourceDoppler Location (LEO) Source 2 Satellite Passes2 Satellite Passes 1 Satellite Pass1 Satellite Pass

Signal Power & TypeSignal Power & Type 0.1 W, Analog0.1 W, Analog 5 W, Digital5 W, Digital

Transmission PeriodTransmission Period ContinuousContinuous ½ Second burst every ½ Second burst every 50 sec. approximately50 sec. approximately

Satellite TypeSatellite Type LEO OnlyLEO Only LEO and GEOLEO and GEO

Alert TimeAlert Time 2 Hours2 Hours(typical)(typical)

InstantaneousInstantaneous(by GEO satellite)(by GEO satellite)

GPS Location AccuracyGPS Location Accuracy NoneNone 10 m (if equipped)10 m (if equipped)

CoverageCoverage LocalLocal GlobalGlobal

Satellite Processing Satellite Processing Phase-out Date (per NOAA)Phase-out Date (per NOAA)

Feb 1, 2009Feb 1, 2009

SARSATSARSATFor More Information…For 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

Documents

SARSAT. COSPAS-SARSAT CospasCOsmicheskaya Systyema Poiska Aariynyich Sudov which translates loosely into “Space System for the Search of Vessels in Distress”