There are two types of LUTs in the Cospas-Sarsat System: those that are designed to operate with the LEOSAR satellite constellation are referred to as LEOLUTs, and those that operate with the GEOSAR satellite constellation are referred to as GEOLUTs.
LEOLUT and GEOLUT operators are expected to provide the SAR community with reliable alert and location data, without restriction on use and distribution. The Cospas-Sarsat Parties providing the space segment, supply LEOLUT and GEOLUT operators with System data required to operate their LUTs. To ensure that data provided by LUTs are reliable and can be used by the SAR community on an operational basis, Cospas-Sarsat has developed LUT performance specifications and procedures. Copies of the LEOLUT and GEOLUT specifications (documents C/S T.002 and C/S T.009) and commissioning standards (documents C/S T.005 and C/S T.010) are available for download under the "System Documents" section of the Professionals website (Pro/Documents).
LEOLUTs
The configuration and capabilities of each LEOLUT may vary to meet the specific requirements of the participating countries, but the Cospas and Sarsat LEOSAR spacecraft downlink signal formats ensure interoperability between the various spacecraft and all LEOLUTs meeting Cospas-Sarsat specifications.
The capability of a LEOLUT is determined, for the most part, by the LEOSAR satellite channels it was designed to process. There are a possible 2 channels that may, depending upon the specific satellite being tracked, be available for processing. Some satellites support all the channels listed below, and some only support a limited set of them.
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The 406-MHz Search and Rescue Processor (SARP) satellite channel transmits received 406-MHz beacon data that has already been partially processed by the satellite to determine the identification, transmit time, and received frequency for each distress beacon transmission burst. Because of the on-board memory capability of the SARP channel, this channel provides global (yet not continuous) coverage for distress beacons that operate at 406 MHz.
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The 406-MHz Search and Rescue Repeater (SARR) channel receives 406-MHz beacon transmission bursts and immediately retransmits them on the satellite downlink. Since there is no memory associated with the repeater channel, this type of processing supports only local mode coverage (i.e., the distress beacon and the LEOLUT must be in simultaneous view of the satellite for a period of time). Furthermore, since the satellite does not process the data, all the processing is performed by the LEOLUT.
For 406-MHz signals received via their respective SARR channel, each transmssion is detected and the Doppler information calculated. A beacon position is then determined using this data. The LUT is also able to provide identification information associated with the beacon.
Processing the SARP channel 2400-bps data (i.e., those generated from 406-MHz transmissions) is relatively straightforward since the Doppler frequency is measured and time-tagged on-board the spacecraft. All 406-MHz data received from the satellite memory on each pass can be processed within a few minutes of pass completion.
To maintain accurate location processing, an update of the satellite ephemeris is produced each time the LUT receives a satellite signal. The downlink carrier is monitored to provide a Doppler signal using the LUT location as a reference, or highly stable 406-MHz calibration beacons at accurately known locations are used to update the ephemeris data.
GEOLUTs
A GEOLUT is a ground receiving station in the Cospas-Sarsat System that receives and processes 406-MHz distress beacon signals which have been relayed by a Cospas-Sarsat geostationary satellite. Due to the extremely large continuous coverage footprint provided by each geostationary satellite, GEOLUTs are able to produce near instantaneous alerting over extremely large areas. However, due to the fact that the satellite remains stationary with respect to distress beacons, GEOLUTs are not able to determine beacon locations using Doppler processing techniques. In view of this, 406-MHz beacons with location protocols allow for the encoding of position data in the transmitted 406-MHz message, thus providing for quasi-real time alerting with position information via the GEOSAR system.
The "GEOLUT Availability Table" provides an indication of which GEOSAR satellite is tracked by which specific GEOLUT (Pro/System/System Monitoring/Availability Tables (QMS)).