Monday, March 31, 2008

406 GPS Personal Locator Beacon

The 406 GPS Personal Locator Beacon (PLB) is designed to be manually deployed and activated. It is only to be activated when all other means of self-rescue have been exhausted. When activated the PLB tells Search and Rescue who you are, where you are, and that you are facing a life threatening situation.

Activate - To activate the PLB in a distress situation, unfasten the antenna from the case and move it into the upright position. Depress the ON/OFF button for 1 full second. Your PLB is now activated. While transmitting your distress signal, the red LED will flash once every 2 seconds alerting you that your PLB is transmitting. An additional BEEP will sound every time your PLB sends off a burst to the satellites (roughly every 50 seconds).

Activation with GPS - This PLB is equipped with an internal GPS receiver. Once activated the GPS engine will start up and search to find your LAT/LON and incorporate it into your 406 MHz signal. As soon as the GPS receiver acquires good positioning data the red LED will stop blinking and the green LED will begin flashing once every 2 seconds.

Once good global positioning data has been obtained, the GPS receiver waits for 20 minutes before looking for new positioning data again. If for any reason a time period of 4 hours passes without the GPS receiver being able to update the last good set of GPS coordinates, the 406 message being transmitted will revert to the default data. At this point the green LED will stop blinking and the red LED will flash once every 2 seconds until new GPS coordinates have been obtained.

THE SEARCH AND RESCUE SYSTEM - The PLB provides a distress message on 406 MHz to satellites of the COSPAS-SARSAT network and to the GEOSAR network that includes GPS latitude and longitude coordinates when GPS data is present.

The message transmitted is unique for each PLB, which provides identification of the transmitter through computer access of registration files maintained by the National Oceanic and Atmospheric Administration. Remember, if your PLB is not registered, Search and Rescue (SAR) Authorities do not know who you are, or how to contact anyone who might know anything about your situation.

Once the signal (406 MHz) is relayed through the LEOSAR and/or GEOSAR network, SAR forces determine who is closest, and then track the signal using the 121.5 MHz homing frequency for intermediate and short-range location.

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 PLB signal, homing must be accomplished at 121.5 MHz.

Global Positioning System (GPS) - The GPS system is a satellite group that enables a GPS receiver to determine its exact position to within 110 yards (100 m) 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 PLB stores this data into its distress transmission allowing search and rescue forces to narrow the search into a very small area and minimize the resources required and dramatically increases the effectiveness of the overall operation.

Satellite Detection - The PLB transmits to the satellite portion of the COSPAS-SARSAT System. COSPAS-SARSAT is an international system that uses Russian Federation and United States low altitude, near-polar orbiting satellites (LEOSAR) that assist in detecting and locating activated 121.5/243 MHz beacons and 406 MHz Satellite beacons.

COSPAS and SARSAT satellites receive distress signals from PLBs 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 beacons 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).