Satellite Detection; Global Positioning System (Gps) - ACR Electronics GLOBAL FIX - REV G Product Support Manual

7.2

Satellite Detection

EPIRBs transmit to the satellite portion of the COSPAS-SARSAT system. COSPAS-SARSAT is an
international system that utilizes Russian Federation and United States' low altitude, near-polar orbiting
satellites (LEOSAR). These satellites assist in detecting and locating activated 406 MHz satellite beacons.
COSPAS and SARSAT satellites receive distress signals from EPIRBs transmitting on the frequency of 406
MHz. The COSPAS-SARSAT 406 MHz beacon signal consists of a transmission of non-modulated carriers
followed by a digital message format that provides identification data. The 406 MHz system uses Satellite-
borne equipment to measure and store the Doppler-shifted frequency along with the beacon's digital data
message and time of measurement. This information is transmitted in real time to an earth station called the
Local User Terminal (LUT), which may be within the view of the satellite, as well as being stored for later
transmission to other LUTs.
The LUT processes the Doppler-shifted signal from the LEOSAR and determines the location of the beacon,
then the LUT relays the position of the distress to a Mission Control Center (MCC) where the distress alert and
location information is immediately forwarded to an appropriate Rescue Coordination Center (RCC). The RCC
dispatches Search and Rescue (SAR) forces.
The addition of the GEOSAR satellite system greatly improves the reaction time for a SAR event. This satellite
system has no Doppler capabilities at 406 MHz, but will relay the distress alert to any of the LUT stations.
When there is GPS data included in the distress message, SAR authorities instantly know your location to
within 110 yards (100 m). This speeds up the reaction time by not having to wait for one of the LEOSAR
satellite to pass overhead. Because most of the search and rescue forces presently are not equipped to home
in on the 406 MHz Satellite beacons signal, homing must be accomplished at 121.5 MHz.
Figure 9- Satellite Coverage
7.3

Global Positioning System (GPS)

The GPS system is a satellite group that enables a GPS
receiver to determine its exact position to within 30 m
(100 ft.) anywhere on earth. With a minimum of 24 GPS
satellites orbiting the earth at an altitude of approximately
11,000 miles they provide users with accurate information
on position, velocity, and time anywhere in the world and
in all weather conditions. The GlobalFix™ stores this data
into its distress transmission allowing search and rescue
forces to narrow the search into a very small area and
thus minimize the resources required and dramatically
increase the effectiveness of the overall operation.
Figure 10- GEOSAR Satellite Orbits
Figure 11 - GPS Satellite Orbits
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