Terminology » Satellite Communication » LEOSAR vs MEOSAR vs GEOSAR: Key Differences Explained

LEOSAR vs MEOSAR vs GEOSAR: Key Differences Explained

leosar meosar geosar search rescue satellite

This article dives into the differences between LEOSAR, MEOSAR, and GEOSAR, all crucial components of the Cospas-Sarsat program. This program is designed to save lives and protect property by providing search and rescue authorities with accurate, reliable, and timely alert and location information. These services are offered free of charge to those in distress worldwide. The program uses a network of satellites and ground systems to detect, process, and relay emergency beacon transmissions operating at 406 MHz.

LEOSAR vs MEOSAR vs GEOSAR

Based on their orbital altitudes, the Cospas-Sarsat system uses three main types of satellites: LEOSAR, MEOSAR, and GEOSAR. Let’s break down each one.

What is LEOSAR?

  • LEOSAR stands for Low Earth Orbiting Search and Rescue.
  • It locates emergency beacons using the Doppler shift effect.
  • The system uses approximately six satellites in low Earth orbit, providing global coverage about twice a day.
  • These satellites orbit at an altitude of about 500 miles in a polar orbit.
  • LEOSAR primarily relies on Doppler locating, rather than GPS, for location determination.
  • LEOSAR satellites store and forward alerts continuously for 48 hours.

What is MEOSAR?

  • MEOSAR stands for Medium Earth Orbit Search and Rescue.
  • The search and rescue receivers are located on GPS satellites operated by the US, Russia, and Europe.
  • This system offers improved position accuracy and decreases the waiting time for rescue.
  • These satellites orbit at an altitude of approximately 19,000 to 24,000 km.
  • MEOSAR offers global coverage and provides near-instantaneous detection and location information.
  • MEOSAR utilizes three or more satellites that receive the beacon signal and use trilateration to calculate the location of the beacon.

What is GEOSAR?

  • GEOSAR stands for Geostationary Orbiting Search and Rescue.
  • It does not have Doppler location capability.
  • The system uses five satellites in geostationary orbit.
  • These satellites are located at an altitude of approximately 23,000 miles in a fixed orbit above the Earth.
  • GEOSAR provides instantaneous alerting but lacks location capability unless the emergency beacon is equipped with GPS.
  • It offers coverage from 70°N to 70°S latitude.
  • The GEOSAR system does not cover polar areas.

LEOSAR vs MEOSAR vs GEOSAR: Key Differences

The following table highlights the key differences between LEOSAR, MEOSAR, and GEOSAR systems:

Comparison ParametersLEOSARMEOSARGEOSAR
Full FormLow Earth Orbiting Search and RescueMedium Earth Orbit Search and RescueGeostationary Orbiting Search and Rescue
Altitude500 miles11,800 to 14,900 miles23,000 miles
Number of satellites in orbit653
Worldwide coverageYesYesNo polar coverage
Real-time continuous accessNo, latency up to several hours until satellite pass, and then potential latency until downlink.YesReal-time continuous access on the covered area but with a less favorable link budget compared to MEOSAR.
Number of satellites simultaneously in visibilityMost of the time, no satellite in view, and in general only one satellite at a time (except for polar areas where multiple visibilities can occur).More than 10 satellites in visibility at any time and anywhere.Only 1 or 2 satellites are in view and, therefore, have important impacts masking effects.
Independent localization of fast-moving beaconsNot availableAvailableNot available