SARSAT (Search & Rescue)

The SARSAT instruments on Metop help search and rescue authorities save thousands of lives around the world.

COSPAS-SARSAT process

COSPAS-SARSAT

The programme coordinates frequency management, satellite, emergency beacon and search and rescue issues, and maintains a national register for 406 MHz emergency beacons. These beacons provide improved performance in comparison to the now obsolete 121.5 MHz and 243 MHz beacons.

The basic Cospas-Sarsat concept comprises various types of distress beacons (aircraft, maritime or personal use) transmitting signals during distress situations.

Since its inception in 1982 Cospas-Sarsat had provided assistance in rescuing more than 37,000 persons in more than 10,000 incidents.

The Sarsat instruments on the Metop satellites, flying in low Earth orbit (LEO) and known as LEOSAR, receive these messages. They are downlinked to the distress terminals — known as Local User Terminals (LUT) — distributed around the globe. The message are then processed and distress alerts generated. The Mission Control Centres (MCC) receive those alerts and relay them to the appropriate Rescue Control Centre (RCC), which begins the actual search and rescue operation.

SARR and SARP-3

Sarsat-11 on Metop-A and Sarsat-13 on Metop-B comprise of SAR signal Repeaters (SARR) and SAR signal Processors (SARP-3).

The SARR instrument receives 406 MHz beacon transmission bursts and retransmits them immediately on the dedicated 1544.5 MHz downlink to the LUTs. Because there isn't a memory within SARR this service only works in local mode, i.e. the beacon and LUT must be in simultaneous view of the satellite. All processing is performed by the LUT. Each transmission is detected and the Doppler (change in wavelength caused by the motion of the satellite, with respect to the beacon) information calculated and a beacon position is then determined.

SARP receives and processes emergency signals from the 406 MHz beacons. It determines the identification, frequency and time of the signal. These pre-processed data are then fed, in real time, to the SARR instrument for immediate transmission, plus simultaneously stored in the memory for additional later transfer to the LUTs. This process can locate beacons within an accuracy of 5 km. A low-power 121.5 MHz homing signal included in most 406 MHz beacons helps rescuers determine the final location.

This means that with a 406 MHz beacon, a distress message can be sent to the appropriate authorities, from anywhere on Earth, 24 hours a day, 365 days a year.

SARR is provided by NOAA and developed by EMS Technologies of Quebec, Canada, under contract to the Canadian Department of National Defense (DND).

SARP-3 is provided by CNES and developed by Thalès Systèmes Aéroportés (TSA).

Under Cospas-Sarsat, EUMETSAT also provides search and rescue transponders on the Meteosat Second Generation geostationary satellites.

Search and Rescue Summary Budget
Power budget SARP: 22 W, SARR: 47 W
TX frequency SARR 1544.5 MHz (± 400 kHz)
RX frequencies SARR: 121.5 (± 20 kHz), 243 (± 30 kHz), 406 MHz (± 80 kHz), SARP: 406 MHz
Data rate 2.4 kbps biphase signal to the SARR Pallet
Processing SARP — three messages received/processed in parallel
Memory capacity SARP — 2048 messages (extended to 2560 by command)
Dimensions SARR RPU: 365mm x 280mm x 194 mm, SARR RX: 458mm x 458mm x 166 mm, SARR TX: 350mm x 369mm x 122mm
Mass SARP RPU: 15kg, SARR RX: 15.2 kg, SARR TX: 5.2kg