SARSAT

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SARSAT
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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.
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SARSAT System Operation
GEO Satellites
LEO Satellites
Local User Terminal
Mission Control Center
Rescue Coordination Center
Emergency Beacons
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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
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Local User Terminals
39 LEOLUT Sites
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Local User Terminals
6 GEOLUTs
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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 Earths 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

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SARSAT A Snapshot in Time
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SARSAT A 3D Look
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LEO and GEO Satellites
Typical Satellite Footprints
GEO Footprint
LEO Footprint
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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
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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 satellites ground
  track

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Doppler Shift Position Solution
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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
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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
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Understanding merges

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

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Doppler Shift Position Solution

• On 406 MHz, the stronger, higher quality signal
  permits using the Doppler shift component of the
  Earths rotation to determine which side of the
  satellite the signal is on
• Thus, 95 of the time, only one satellite pass is
  needed

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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

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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

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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

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Problems with 121.5 MHz Alerting

• Number of False Alerts
• Timeliness
• Accuracy
• Identification
• Reliability/Operation

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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

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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

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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
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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

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A Typical Day at AFRCC
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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

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Variations and Capabilities Recap 121.5/243 MHz
vs. 406 MHz
121.5/243 MHz 406 MHz
Doppler Location Accuracy (90) 11 NM 3 NM
Doppler Location (LEO) Source 2 Satellite Passes 1 Satellite Pass
Signal Power Type 0.1 W, Analog 5 W, Digital
Transmission Period Continuous ½ Second burst every 50 sec. approximately
Satellite Type LEO Only LEO and GEO
Alert Time 2 Hours(typical) Instantaneous(by GEO satellite)
GPS Location Accuracy None 10 m (if equipped)
Coverage Local Global
Satellite Processing Phase-out Date (per NOAA) Feb 1, 2009
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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