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).
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.
Receiving alerts from ships. Determining the position of the ship. Distributing alerts. Co-ordination between SAR efforts.
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)
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.
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 deployedII. Manually deployed
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.
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.
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.
The ambiguity can be resolvedusing the above equation &knowing the Earth velocityvector. However this depends onthe stability of the beacon’sfrequency, thus it is only possiblefor modern 406 MHz.
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.
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)
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
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.
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.
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.
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.
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