The satellite detection network was built after the ELT beacons were already in general use, with the first satellite not being launched until 1982, and even then, the satellites only provided detection, with location accuracy being roughly 20 km (12 mi). The frequency and signal format used by the ELT beacons was not designed for satellite detection, which resulted in a system with poor location detection abilities and long delays in detection of activated beacons. military, and were mandated for use on many types of commercial and general-aviation aircraft beginning in the early 1970s. These beacons were first used in the 1950s by the U.S. The first form of these beacons was the 121.5 MHz ELT, which was designed as an automatic locator beacon for crashed military aircraft. It is distinct from a satellite emergency position-indicating radiobeacon station. It is an internationally regulated mobile radiocommunication service that aids search-and-rescue operations to detect and locate distressed watercraft, aircraft, and people. The standard frequency of a modern EPIRB is 406 MHz. Previous emergency beacons without a GPS can only be localized to within 2 km (1.2 mi) by the COSPAS satellites and relied heavily upon the 121.5 MHz homing signal to pin-point the beacons location as they arrived on scene. The feature distinguishing a modern EPIRB, often called GPIRB, from other types of emergency beacon is that it contains a GPS receiver and broadcasts its position, usually accurate within 100 m (330 ft), to facilitate location. The basic purpose of this system is to help rescuers find survivors within the so-called "golden day" (the first 24 hours following a traumatic event) during which the majority of survivors can usually be saved. As Search and Rescue approach the search areas, they use Direction Finding (DF) equipment to locate the beacon using the 121.5 MHz homing signal, or in newer EPIRBs, the AIS location signal. The satellites calculate the position or utilize the GPS coordinates of the beacon and quickly passes the information to the appropriate local first responder organization, which performs the search and rescue. The signal is detected by satellites operated by an international consortium of rescue services, COSPAS-SARSAT, which can detect emergency beacons anywhere on Earth transmitting on the distress frequency of 406 MHz. In the event of an emergency, such as a ship sinking or medical emergency onboard, the transmitter is activated and begins transmitting a continuous 406 MHz distress radio signal, which is used by search-and-rescue teams to quickly locate the emergency and render aid. First generation EPIRB emergency locator beaconsĪn emergency position-indicating radiobeacon ( EPIRB) is a type of emergency locator beacon for commercial and recreational boats, a portable, battery-powered radio transmitter used in emergencies to locate boaters in distress and in need of immediate rescue. Overview diagram of COSPAS-SARSAT communication system used to detect and locate ELTs, EPIRBs, and PLBs. For broader coverage of this topic, see Emergency locator beacon.
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