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Encyclopedia > Emergency Locator Transmitter

Emergency position-indicating rescue beacons (EPIRB), also called Emergency Locator Transmitter (ELT) or Personal Locator Beacon, are small radio transmitters that some satellites and search and rescue aircraft can use to locate people, boats and aircraft needing rescue. They are a component of the Global Maritime Distress Safety System. See the U.S. center's website. This page discusses Beacons, fires designed to attract attention. ... Crystal Palace transmitter, London A transmitter is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... A satellite is an object that orbits another object (known as its primary). ... Search and Rescue (acronym SAR) is an operation mounted by emergency services, often well-trained volunteers, to find someone believed to be in distress, lost, sick or injured either in a remote or difficult to access area, such as mountains, desert or forest (Wilderness search and rescue), or at sea... An aircraft is any machine capable of atmospheric flight. ... A boat is a watercraft, usually smaller than most ships. ... An aircraft is any machine capable of atmospheric flight. ... The Global Maritime Distress Safety System (GMDSS) is an internationally-agreed set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships, boats and aircraft. ...


The basic purpose of the emergency beacons is to get people rescued within the "golden day" when the majority of survivors can still be saved.


Between 1982 and 2002, these systems enabled the rescue of 14,700 people. As of 2002, there are roughly 82,000 registered beacons, and over 500,000 of the older unregistered type.

Most beacons are brightly-colored, waterproof, fit in a cube about 30 cm on a side, and weigh 2-5 kg. They can be purchased from marine suppliers, aircraft refitters, and (in Australia and the United States) hiking supply stores. The units have a useful life of 10 years, operate across a range of conditions (-40°C to 40°C), and transmit for 24 to 48 hours. As of 2003 the cost varies from US$139 to US$3000, with varying performances (see below). Although modern systems are significantly superior to older ones, even the oldest systems provide an immense improvement in safety, compared to not having a beacon. picture of 1st generation Epirbs File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... 2003 is a common year starting on Wednesday of the Gregorian calendar. ...

Contents


Statutory Emergency equipement

Most general aviation aircraft in the U.S. are required to carry an ELT, while most commercial airliners are not.


Most commercial off-shore working vessels with passengers are required to carry a self-deploying EPIRB, while most in-shore and fresh-water craft are not.


Types

There are two types: manually activated, and automatically activated.


In the U.S., offshore beacons are investigated and victims rescued by the Coast Guard. On-shore beacons are investigated by local search and rescue services in Alaska. The Air Force Rescue Coordination Center is charged with land-based emergency signals, usually dispatching volunteer members from The United States Air Force Auxiliary Civil Air Patrol. In the U.S. there are no published notification systems for other locations. U.S. Coast Guard helicopter A coast guard is an organization devoted to saving the lives of shipwrecked mariners or people in danger at sea. ... Civil Air Patrol members searching for an emergency locator transmitter The Civil Air Patrol (CAP) is the official civilian auxiliary of the United States Air Force (USAF). ...


In the U.S. no special license is required, but serial-number registration is required. Nearly all U.S.-registered aircraft are required to carry an ELT. In some jurisdictions, larger boats and ships are required to carry them. An aircraft is any machine capable of atmospheric flight. ... A boat is a watercraft, usually smaller than most ships. ... Italian barque Amerigo Vespucci in New York harbor, 1976. ...


Current types

Current EPIRBs are generally divided into three classes; Category I, Category II, and Class B (or Category B).

  • Category I EPIRBs are considered the best but are also the most costly. Category I EPIRBs can be either activated manually or set to activate automatically in the event of a disaster at sea. These EPIRBs are generally housed in a specially designed bracket on deck and the buoyant beacon is designed to rise to the surface and emit two signals, an emergency homing signal on 121.5 MHz and a digital identification code on 406 MHz that can be used to identify the stricken vessel. Category I EPIRBs used in American waters must be registered with NOAA.
  • Category II EPIRBs are similar to Category I EPIRBs but are generally manual activation only. Also like Category I EPIRBs, Category II units must be registered. Category II EPIRBs are also generally less costly averaging less than US$1,000.
  • Class B EPIRBs, also called Category B or "Mini B", operate a 121.5 MHz homing signal only and are usually manual activation only units. They are the cheapest units but also the least capable. Since the signal has no identification component, Class B EPIRBs are not registered. Due to their limitations, Class B EPIRBs are slowly being phased out. The International COSPAR-SARSAT program will no longer monitor Category B EPIRB signals as of February 1, 2009. Although the U.S. Coast Guard no longer recommends them, they remain in wide use.

A distress signal is an internationally recognized means of obtaining help by using a radio, displaying a visual object or making noise from a distance. ... A distress signal is an internationally recognized means of obtaining help by using a radio, displaying a visual object or making noise from a distance. ... February 1 is the 32nd day of the year in the Gregorian Calendar. ... 2009 is a common year starting on Thursday of the Gregorian calendar. ...

Obsolete types

There are also several older types of EPIRB devices which are no longer recommended for use.

  • Class A - A 121.5 MHz automatic activation unit. Due to limited signal coverage and possible lengthy delays in signal recognition, the U.S. Coast Guard no longer recommends use of this type.
  • Class C - Operates on VHF channel 15/16. Designed for small crafts operating close to shore, this type was only recognized in the United States. Use of these units was phased out in 1999.
  • Class S - A 121.5 MHz unit similar to Class B but is often included as an integral part of a lifeboat or survival suit. Their use is no longer recommended by the U.S. Coast Guard.
  • Inmarsat E - entered service in 1997. The unit is an automatic activation unit operating on 1646 MHz and detectable by the Inmarsat geostationary satellite system. This class of EPIRB was approved by the Global Maritime Distress Safety System (GMDSS), but not by the United States. In September 2004, Inmarsat announced that it was terminating its Inmarsat E EPIRB service as of December 2006 due to a lack of interest in the maritime community.

Furthermore, the U.S. Coast Guard recommend that no EPIRB of any type manufactured before 1989 be used. Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ... 1999 is a common year starting on Friday of the Common Era, and was designated the International Year of Older Persons by the United Nations. ... 1997 is a common year starting on Wednesday of the Gregorian calendar. ... The Global Maritime Distress Safety System (GMDSS) is an internationally-agreed set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships, boats and aircraft. ... September is the ninth month of the year in the Gregorian Calendar and one of four Gregorian months with the length of 30 days. ... 2004 is a leap year starting on Thursday of the Gregorian calendar. ... December is the twelfth and last month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ...


Registration

Modern emergency beacons transmit a serial number. When the beacon is purchased this number should be registered with the relevant national authority. Registration provides the national authority with phone numbers to call, and a description of the signaling vessel, including its home port. The registration can give much of the information needed for starting the rescue. Also, they provide an easy way for the notification services to check and eliminate false alarms quickly.


How they work

All the systems work something like this: A beacon is activated by a crash, a sinking, or manually by survivors. The beacon's transmission is picked up by one or more satellites. The satellite transmits the beacon's signal to its ground control station. The satellite's ground station processes the signals and forwards the data, including approximate location, to a national authority. The national authority forwards the data to a rescuing authority. The rescuing authority uses its own receiving equipment to locate the beacon and makes the rescue or recovery. Once the satellite data is in, it takes less than a minute to frward the data to any signatory nation.

Overview diagram of EPIRB/COSPAS-SARSAT communication system
Enlarge
Overview diagram of EPIRB/COSPAS-SARSAT communication system

There are several systems in use, with beacons of varying expense, different types of satellites and varying performance. From NOAA / COSPAS SARSAT File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... From NOAA / COSPAS SARSAT File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


GPS-based, registered

The most modern 406 MHz beacons with GPS (US$ 1200-$3000 in 2002) locate a beacon with a precision of 100 meters, anywhere in the world, and send a serial number so the government authority can look-up phone numbers to notify next-of-kin in four minutes, with rescue commencing shortly afterward. The GPS system permits stationary, wide-view geosynchronous communications satellites to report the location (doppler location, see below, is not needed). If any of the system breaks down, yet the beacon works, it defaults to the performance of the compatible intermediate technology beacon, below. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...


High-precision registered

An intermediate technology 406 MHz beacon (US$ 900-500) has world-wide coverage, locates within 2 km. (12.5 km² search area), notifies kin and rescuers in 2 hours maximum (46 min avg.), and has a serial number to look up phone numbers, etc. This can take up to two hours because it has to use moving weather satellites to locate the beacon. To help locate the beacon, the beacon's frequency is controlled to 2 parts per billion, and its power is a hefty five watts.


Both of the above types of beacons usually include an auxiliary 25 milliwatt beacon at 121.5 MHz to guide rescue aircraft. A distress signal is an internationally recognized means of obtaining help by using a radio, displaying a visual object or making noise from a distance. ...


Traditional ELT, unregistered

The oldest, cheapest (US$ 139) beacons send an anonymous warble at 121.5 MHz. They work over only 60% of the earth, require up to 6 hours for notification, locate within 20 km (search area of 1214 km²) and are anonymous. Coverage is partial because the satellite has to be in view of both the beacon and a ground station at the same time - the satellites do not store and forward the beacon's position. Coverage in polar and south-hemisphere areas is bad. The frequency is the standard aviation emergency frequency, and there is interference from other electronic and electrical systems, so false alarms are common. To reduce false alarms, a beacon is confirmed by a second satellite pass, which slows notification to 4 hours. Also, the beacons can't be located as well because their frequency is only accurate to 50 parts per million, and they send only 75-100 milliwatts of power. A distress signal is an internationally recognized means of obtaining help by using a radio, displaying a visual object or making noise from a distance. ...


By international agreement, these original 121.5 MHz (civil) and 243 MHz (military) beacons will no longer be sensed by satellites starting in 2009.


Note that even the oldest systems provide an immense improvement in safety, compared to not having a beacon.


Location by Doppler (without GPS)

When the beacon has no GPS receiver, the system locates the beacon from its doppler shift as received by the quickly-moving satellites. Basically, the frequency received varies depending on the speed of the beacon relative to the satellite. The amount of doppler is proportional to the range and bearing to the satellite. The instant the beacon's doppler shift changes from high to low indicates the time when the bearing from the beacon to the satellite's ground track is 90 degrees. The side of the satellite track is determined because the rate of change of the doppler is faster when the Earth is turning towards the satellite track. The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ...


In order to handle multiple simultaneous beacons, modern 406 MHz beacons transmit in bursts, and remain silent for a few seconds. This also conserves transmitter power.


The Russians developed the original system, and its success drove the desire to develop the improved 406 MHz system. The original system is a brilliant adaptation to the low quality beacons, originally designed to aid air searches. It uses just a simple, lightweight transponder on the satellite, with no digital recorders or other complexities. Ground stations listen to each satellite as long as it is above the horizon. Doppler shift is used to locate the beacon(s). Multiple beacons are separated when a computer program performs a Fourier transform on the signal. Also, two satellite passes per beacon are used. This eliminates false alarms by using two measurements to verify the beacon's location from two different bearings. This prevents false alarms from VHF channels that affect a single satellite. Regrettably, the second satellite pass almost doubles the average time before notification of the rescuing authority. However the notification time is much less than a day. The Fourier transform, named after Jean Baptiste Joseph Fourier, is an integral transform that re-expresses a function in terms of sinusoidal basis functions, i. ...


Satellites used

Receivers are auxiliary systems mounted on several types of satellites. This substantially reduces the program's cost.


The weather satellites that carry the SARSAT receivers are in "ball of yarn" orbits, inclined at 99 degrees. The longest period that all satellites can be out of line-of-sight of a beacon is about two hours.


The first satellite constellation was launched in the early 1970s by Soviet Russia, Canada, France and the U.S.


Some geosynchronous satellites have beacon receivers. Since end of 2003 there are four such geostationary satellites (GEOSAR) that cover more than 80% of the surface of the earth. As with all geosynchronous satellites, they are located above the equator. The GEOSAR satellites do not cover the polar caps.


Since they see the Earth as a whole, they see the beacon immediately, but have no motion, and thus no doppler frequency shift to locate it. However, if the beacon transmits GPS data, the geosynchronous satellites give nearly instantaneous response.


History

The original impetus to the program in the U.S. was the loss of two congressmen in the Alaskan wilderness in 1970. A massive search effort failed to locate them. The result was a U.S. law mandating that all aircraft carry an emergency locator transmitter. Technical and organizational improvements followed.


COSPAS/SARSAT is an international organization that has been a model of international cooperation, even during the Cold War. SARSAT means Search And Rescue SATellite. COSPAS is a Russian acronym with the same meaning. A consortium of Russia, the U.S., Canada and France formed the organization in 1982. Since then 29 others have joined. The Cold War was the open yet restricted rivalry that developed after World War II between the United States and its allies and the Soviet Union and its allies. ...


COSPAS/SARSAT defines standards for beacons, auxiliary equipment to be mounted on conforming weather and communication satellites, ground stations, and communications methods. The satellites communicate the beacon data to their ground stations, which forward it to main control centers of each nation that can initiate a rescue effort.


The U.S. Coast Guard once promoted an emergency beacon on maritime VHF emergency channels. It now promotes the superior COSPAS/SARSAT system, and no longer services emergency beacons on maritime VHF frequencies.


See also

Shipboard Global Maritime Distress Safety System (GMDSS) installations include one or more search and rescue radar transponder (SART) devices which are used to locate a survival craft or distressed vessel by creating a series of dots on a rescuing ships radar display. ...

References

COSPAS-SARSAT, Document C/S T.001 October 99 RTCM, Standard for 406 MHz Satellite EPIRBs FCC, Part 80 and GMDSS MED, 0735/2001 The Global Maritime Distress Safety System (GMDSS) is an internationally-agreed set of safety procedures and types of equipment used to increase safety and make it easier to rescue distressed ships, boats and aircraft. ...


External links


  Results from FactBites:
 
Ultralife Powers ELTs - Ultralife Batteries, Inc. | Application Stories (446 words)
An Emergency Locator Transmitter (ELT) is a radio-frequency transmitter that generates a signal to assist in search and rescue (SAR) for missing aircraft.
In theory, an ELT is activated when subjected to the forces of a crash impact, or manually by survivors.
The international group responsible for monitoring and locating ELTs via satellite has announced a 9-year phase-out of the older ELT program, to be completed in early 2009.
  More results at FactBites »

 
 

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