COSPAS-SARSAT (COSPAS: Space System for the Search of Vessels in Distress; SARSAT: Search And Rescue Satellite-Aided Tracking) is a SAR (Search And Rescue) system utilizing both Polar orbiting and Geostationary (Geosynchronous) satellites, which provides Distress alerting and location information to SAR services for aviation, maritime and land users. There are at present three types of Distress beacons which utilize the system:
  • EPIRB – Emergency Position Indicating Radio Beacon (Maritime)
  • ELT – Emergency Locator Transmitter (Aviation)
  • PLB – Personal Locator Beacons (Land)
These beacons transmit radio signals on 406 MHz that are detected by COSPAS-SARSAT polar orbiting and geostationary satellites. Information is subsequently relayed, together with location and ID of casualty through Earth based LUT (Local User Terminals) and MCC (Mission Control Centres) to the appropriate MRCC (Maritime Rescue and Coordinating Centre) which coordinates all SAR unit deployment in the SAR region where the casualty is located.

COSPAS-SARSAT space segment

COSPAS-SARSAT system utilize SAR packages on satellites in (LEOSAR) Low-altitude Earth Orbit and (GEOSAR) Geostationary Earth Orbit.

LEOSAR and GEOSAR satellites

LEOSAR and GEOSAR satellites in the COSPAS-SARSAT System

LEOSAR

The LEOSAR system configuration comprises 4 satellites, 2 COSPAS (Russia) and 2 SARSAT (USA, Canada and France) in near North-South polar orbit, with an orbital period of approximately 120 minutes. The orbits of these satellites are arrange to scan the entire surface of the Earth. The satellites view an area of the Earth over 6000 km wide as they orbit the globe, giving an instantaneous field of view or footprint (like the illumination from a torch beam) about the size of a continent.

LEOSAR sattelite path

LEOSAR satellite path and footprint

The coverage is not continuous due to the orbital period of the satellite. By the nature of the polar orbits, the waiting time for detection, can be greater in equatorial regions than at higher latitudes, on average it is 45 minutes.

When the LEOSAR system detects Distress alert, it calculates the location of the Distress event using Doppler processing techniques. Doppler processing is based upon the principle that the frequency of the distress beacon, as "heard" by the satellite instrument, is affected by the relative velocity of the satellite with respect to the beacon. By monitoring the change of the beacon frequency of the received beacon signal and knowing the exact position of the satellite, the LEOSAR system is able to calculate the location of the beacon with an accuracy of within 5-10 km.

GEOSAR

The GEOSAR system configuration comprises 4 geostationary satellites located at approximately 36000 km above the Equator at different lines of longitude, giving an instantaneous footprint of the whole of the Earths surface nominally between 700 North and 700 South.

GEOSAR satellite coverage map

GEOSAR coverage areas

In contrast with the LEOSAR satellites the GEOSAR satellites provide continuous coverage only of a major portion of the Earth between 700 North and 700 South with near immediate alerting capability, but they cannot determine the location of the Distress event, because they are fixed with the respect to the earth so they cannot use Doppler processing techniques. The location of the Distress event must be either:
  • acquired by the beacon through an internal or an external position fixing system, for example GPS or Glonass, and encoded in the beacon message, or
  • derived, with possible delays, from the LEOSAR System.

LEOSAR and GEOSAR capabilities comparison


LEOSAR

GEOSAR

Location information

provided using Doppler processing techniques available only if encoded in beacon message

Location accuracy

+/- 5 km
if acquired from GPS: within 10 m

Coverage area

the entire surface of the Earth a major portion of the Earth between 700 North and 700 South

Distress event detection

the waiting time for detection is on average 45 minutes
near instantaneous

EPIRBs able to utilize the combined system are now available, having a built in GPS position fixing system. They enables near instantaneous distress event detection with location information included so the SAR operation can start immediately.

COSPAS-SARSAT earth segment

LUT - Local Users Terminal

LEOLUT and GEOLUT Earth based ground stations, receive and process Distress alerts from 406 MHz EPIRBs relaying Distress information, comprising casualty ID, Position and UTC time, to MCC (Mission Control Centres).

MCC - Mission Control Centres

Their main purpose and function is to relay EPIRB Distress alert information to the appropriate MRCC who coordinates the deployment of SAR units in the SAR region in which the casualty is located.

Last modified: Saturday, 25 April 2020, 7:50 PM