3. Cospas-Sarsat is an international satellite-based search
and rescue (SAR) distress alert detection and
information distribution system, established by
Canada, France, the United States, and the former Soviet
Union in 1979.
COSPAS (КОСПАС) is an acronym for the Russian words
"Cosmicheskaya Sistema Poiska Avariynyh Sudov"
(Космическая Система Поиска Аварийных
Судов), which translates to "Space System for the
Search of Vessels in Distress". SARSAT is an acronym for
Search And Rescue Satellite-Aided Tracking.
COSPAS-SARSAT is an element of the GMDSS (Global
Maritime Distress Safety System).
4. The objective of the Cospas-Sarsat system
is to reduce, as far as possible, delays in the
provision of distress alerts to SAR
services, and the time required to locate a
distress and provide assistance, which have
a direct impact on the probability of survival
of the person in distress at sea or on land.
5. Receiving alerts from ships.
Determining the position of the ship.
Distributing alerts.
Co-ordination between SAR efforts.
6. The system consists of two segments:
The ground segment:
1. Distress Radio Beacons (EPIRB).
2. Local User Terminals (LUT).
3. Mission Control Centers (MCC).
The space segment:
Contains SAR Processors (SARP) on board of:
1. LEOSARs (Low Earth Orbit SAR)
2. GEOSARs (Geostationary Earth Orbit SAR)
7. Emergency Position-Indicating Radio Beacon
Operating frequency: 406 MHz, channel is 3 kHz wide and
centers range from 406.022 to 406.076 MHz which make up
19 channels.
Emits a 5 watt signal with an accuracy of 2dB for 0.5 seconds
every 50 seconds (Pulse mode).
The message contains a 15, 22 or 30 digits Hex code.
The code contains the country of beacon
registration, identification of the ship, optionally position
information from on-board GPS.
Second generation 406 MHz beacons have been introduced
since 1997 which allow for the transmission of encoded
position data acquired by the beacons from GPS, using
internal or external GPS receivers.
8. All 406 MHz beacons are
registered.
Starting on 1 February
2009, the Cospas-Sarsat
system stopped processing
signals from the
121.5 MHz and 243 MHz
beacons.
Two categories:
I. Automatically deployed
II. Manually deployed
9. Low Earth Orbit Local User Terminal
These receive the downlink from the LEOSAR,
processes the signal & then sends it over to
the MCC.
The processing includes Doppler frequency
shift processing for determining the location
of the distressed ship.
The downlink frequency is
1544.5 MHz with the receiver
bandwidth of 1 kHz.
10.
11. The Doppler effect (or Doppler shift), named
after Austrian physicist Christian Doppler who
proposed it in 1842, is the change in frequency
of a wave “as heard” for an observer moving
relative to the source of the wave.
12. The point of inflection of the curve
represents the point in time where the
satellite was closest to the transmitter (TCA
- Time of Closest Approach).
The slope of the curve at TCA determines
the distance of the transmitter from the
satellite track.
It is possible to plot two lines which
represent the distance from the satellite
track where the transmitter could have
been.
Knowing the time of closest approach of
the satellite, it is a simple matter of
drawing a perpendicular line from the point
on the satellite track at TCA to the lines
representing the distance between the
transmitter and the satellite track.
This gets two possible locations for the
transmitter, one being the actual location
and the other being its mirror image.
A subsequent satellite pass on a different
satellite track can be used to resolve the
ambiguity.
13. The ambiguity can be resolved
using the above equation &
knowing the Earth velocity
vector. However this depends on
the stability of the beacon’s
frequency, thus it is only possible
for modern 406 MHz.
14. Geostationary Earth Orbit Local User Terminal
Used for processing signals from GEOSARs.
The receiver center frequency is 1544.5 MHz. The
bandwidth is approximately 100 kHz to match the
downlink translation bandwidth. The allocated
bandwidth for this service is wider, 1 MHz centered at
1544.5 MHz.
The downlink EIRP shall be a minimum of 15 dBW.
The minimum G/T ratio should be -16dBW.
Polarization is either linear or RHCP.
15.
16. Mission Control Center
MCCs are responsible for receiving and
distributing distress signal alerts from distress
radiobeacons.
The functions of an MCC are:
To collect, store and sort the data from LUTs and
other MCCs.
To provide international and national data
exchange within the Cospas-Sarsat System.
To distribute alert and location data to associated
Joint Rescue Coordination Centers (RCCs) or SAR
Points of Contact (SPOCs)
17. Low Earth Orbit Search And Rescue Satellite.
LEOSAR satellites are monitored by 44 LEOLUTs.
Orbit at a height of about 1000 km above Earth surface.
The LEOSAR satellites provide periodic coverage of the entire
earth with an emphasis on polar regions.
The LEOSAR satellites operate in a store-and-forward mode for
406 MHz signals. They store distress signals, measure the
Doppler frequency shift, time-tag the information and forward
them to the next LEOLUT ground station they overfly.
The 6-satellite polar-orbit constellation LEOSAR system provides
frequent coverage of the poles with approximately 100 minute
orbits.
Sarsat-7 SARP aboard NOAA-15
Sarsat-8 SARP aboard NOAA-16
Sarsat-9 SARP aboard NOAA-17
Sarsat-10 SARP aboard NOAA-18
Sarsat-11 SARP aboard METOP-A
Sarsat-12 SARP aboard NOAA-19
18. Geostationary Earth Orbit Search And Rescue
Satellite.
These compliment the LEOSARs.
They have the advantage of being able to
forward distress signals in 4 minutes time to
GEOLUTs.
The GPS location of the distressed ship may be
included in the message which determines
position to within.
The polar regions are not covered at all &
regions beyond 70 degrees above or below the
equator are not well covered.
There are 5 Geostationary satellites that carry
SAR processors.
The GOES geostationary satellites GOES-East at
75° W and GOES-West at 135° W
The INSAT-3A geostationary satellite at 93.5° E
The Meteosat Second Generation (MSG)
geostationary satellites MSG-1 at 9.5° E and
MSG-2 fixed over the Prime Meridian.
The uplink frequency band is100 kHz
bandwidth centered on 406.05 MHz.
19. The EPIRB is deployed either manually or
automatically.
It is activated once touching sea water.
It sends a signal every 50 seconds containing the
ship identification & possibly a GPS acquired
position.
The signal is received by LEOSARs & GEOSARs.
LEOSARs receive the signal when the beacon
comes within the satellite footprint.
GEOSARs receive signals almost instantly if the
beacon is within coverage of the satellite.
20.
21. The LUTs determine the position & send it along with
the identification code of the ship to the MCCs.
MCCs identify the distressed ship from their Database
using the identification code.
22.
23. MEOSAR (Medium Earth Orbit Search And Rescue)
Supporters of the Cospas-Sarsat system are working to
add a new capability called MEOSAR.
In its current form, it is being called the Distress Alerting
Satellite System (DASS) by NASA. This system will put SAR
processors aboard the GPS satellite constellation and the
Galileo positioning system constellation.
MEOSAR satellites will be able to provide near-
instantaneous detection, identification, receipt of encoded
position, and determination of Doppler triangulated
position of 406 MHz beacons. MEOSAR assets will report
signals from Cospas-Sarsat search and rescue beacons in
the 406.0–406.1 MHz band. There is also the possibility
that the system will be able to download information back
to the distress radio beacon via the GPS downlink.
24. www.cospas-sarsat.org
RSS-287, EPIRB, ELT, PLB
417-R-IRD-0006, 2003, Geostationary Operational
Environmental Satellite (GOES), GOES-R Series Interface
Requirements Document (IRD), Space Segment (SS) To
Search and Rescue (SAR) Service
http://www.epirb.org/cospassarsat/406mhz/index.htm
D. H. Evans and W. N. McDicken, Doppler
Ultrasound, Second Edition, John Wiley and Sons, 2000.
GNSS Doppler Positioning, Mojtaba Bahrami, Geomatics
Lab. @ CEGE Dept., University College London
Global Mobile Satellite Communications For Maritime, Land
and Aeronautical Applications, Ilcev, Stojce
Dimov, 2005, XXIV
