Operation Emergency position-indicating radiobeacon station

1 operation

1.1 activation

1.1.1 automatic hydrostatic release unit


1.2 beacon operation

1.2.1 gps-based, registered
1.2.2 high-precision registered
1.2.3 traditional elt, unregistered
1.2.4 location doppler (without gps)


1.3 satellites
1.4 search , rescue response
1.5 operational testing

operation

a transmission gets processed follows:

once satellite data received, takes less minute forward signatory nation.

overview diagram of epirb/cospas-sarsat communication system

there several systems in use, beacons of varying expense, different types of satellites , varying performance. carrying oldest systems provides immense improvement in safety on carrying none.

activation

there 2 ways activate beacon:

manually
automatically

automatic epirbs water activated, while automatic elts have impact monitors activated g-force. epirbs deploy ; means physically depart mounting bracket on exterior of vessel (usually going water.)

for marine epirb begin transmitting signal (or activate ) first needs come out of bracket (or deploy ). deployment can happen either manually must physically remove bracket or automatically water pressure cause hydrostatic release unit separate epirb bracket. if not come out of bracket not activate. there magnet in bracket operates reed safety switch in epirb. prevents accidental activation if unit gets wet rain or shipped seas.

once deployed, epirbs can activated, depending on circumstances, either manually (crewman flicks switch) or automatically (when water contacts unit s sea-switch .) modern epirbs provide both methods of activation , deployment, , labelled manual , automatic deployment , activation.

automatic hydrostatic release unit

a hydrostatic release unit or hru pressure activated mechanism designed automatically deploy when conditions met. in marine environment occurs when submerged maximum depth of 4 meters. pressure of water against diaphragm within sealed casing causes plastic pin cut thereby releasing containment bracket casing, allowing epirb float free.

epirb hydrostatic release mechanism

some common characteristics of hrus are:

water pressure sensitive @ depths not exceed 4 meters or less 2 meters
single use only, require replacement if activated
cannot serviced; replaced
waterproof; sealed against moisture , tampering
must labeled expiration date
expiration date 2 years month of installation applies unit , rod

several regulations , technical specifications govern epirb hydrostatic release devices:

iso 15734
solas 74.95
cfr title 46 vol 6 section 160.062
uscg 160.162






beacon operation
gps-based, registered

406 mhz beacons gps track precision of 100 meters in 70% of world closest equator, , send serial number responsible authority can phone numbers notify registrator (e.g., next-of-kin) in 4 minutes.

the gps system permits stationary, wide-view geosynchronous communications satellites enhance doppler position received low earth orbit satellites. epirb beacons built-in gps called gpirbs, gps position-indicating radio beacon or global position-indicating radio beacon.

however, rescue cannot begin until doppler track available. cospas-sarsat specifications beacon location not considered resolved unless @ least 2 doppler tracks match or doppler track confirms encoded (gps) track. 1 or more gps tracks not sufficient.

high-precision registered

an intermediate technology 406 mhz beacon (now obsolete in favor of gps enabled units) has worldwide coverage, locates within 2 km (12.5 km² search area), notifies kin , rescuers in 2 hours maximum (46 min average), , has serial number phone numbers, etc. can take 2 hours because has use moving weather satellites locate beacon. locate beacon, beacon s frequency controlled 2 parts per billion, , power 5 watts.

both of above types of beacons include auxiliary 25 milliwatt beacon @ 121.5 mhz guide rescue aircraft.

traditional elt, unregistered

the oldest, cheapest beacons aircraft emergency locator transmitters (elts) send anonymous warble on aviation band distress frequency @ 121.5 mhz. frequency routinely monitored commercial aircraft, has not been monitored satellite since feb. 1, 2009.

these distress signals detected satellite on 60% of earth, required 6 hours notification, located within 20 km (12 mi) (search area of 1200 km²), anonymous, , couldn t located because frequency accurate 50 parts per million , signals broadcast using 75–100 milliwatts of power. coverage partial because satellite had in view of both beacon , ground station @ same time – satellites did not store , forward beacon s position. coverage in polar , south-hemisphere areas poor.

false alarms common, beacon transmitted on aviation emergency frequency, , there interference other electronic , electrical systems. reduce false alarms, beacon confirmed second satellite pass, slow confirmation of case of distress 4 hours (although in rare circumstances satellites position such immediate detection becomes possible.)

location doppler (without gps)

the cospas-sarsat system made possible doppler processing. local unit terminals (luts) detecting non-geostationary satellites interpret doppler frequency shift heard leosar , meosar satellites pass on beacon transmitting @ fixed frequency. interpretation determines both bearing , range. range , bearing measured rate of change of heard frequency, varies both according path of satellite in space , rotation of earth. triangulates position of beacon. faster change in doppler indicates beacon closer satellite s orbit. if beacon moving toward or away satellite track due earth s rotation, on 1 side or other of satellite s path. doppler shift 0 @ closest point of approach between beacon , orbit.

if beacon s frequency more precise, can located more precisely, saving search time, modern 406 mhz beacons accurate 2 parts per billion, giving search area of 2 square km, compared older beacons accurate 50 parts per million had 200 square kilometers of search area.

in order increase useful power, , handle multiple simultaneous beacons, modern 406 mhz beacons transmit in bursts, , remain silent 50 seconds.

russia developed original system, , success drove desire develop improved 406 mhz system. original system brilliant adaptation low quality beacons, designed aid air searches. used simple, lightweight transponder on satellite, no digital recorders or other complexities. ground stations listened each satellite long above horizon. doppler shift used locate beacon(s). multiple beacons separated when computer program analysed signals fast fourier transform. also, 2 satellite passes per beacon used. eliminated false alarms using 2 measurements verify beacon s location 2 different bearings. prevented false alarms vhf channels affected single satellite. regrettably, second satellite pass doubled average time before notification of rescuing authority. however, notification time less day.

satellites

receivers auxiliary systems mounted on several types of satellites. substantially reduces program s cost.

the weather satellites carry sarsat receivers in ball of yarn orbits, inclined @ 99 degrees. longest period satellites can out of line-of-sight of beacon 2 hours.

the first satellite constellation launched in 1970s soviet union, canada, france , united states.

some geosynchronous satellites have beacon receivers. since end of 2003, there 4 such geostationary satellites (geosar) cover more 80% of surface of earth. geosynchronous satellites, located above equator. geosar satellites not cover polar caps.

since see earth whole, see beacon immediately, have no motion, , no doppler frequency shift locate it. however, if beacon transmits gps data, geosynchronous satellites give instantaneous response.

search , rescue response

emergency beacons operating on 406 mhz transmit unique 15, 22, or 30 character serial number called hex code. when beacon purchased, hex code should registered relevant national (or international) authority. registration provides search , rescue agencies crucial information such as:

phone numbers call,
a description of vessel, aircraft, vehicle, or person (in case of plb)
the home port of vessel or aircraft
any additional information may useful sar agencies

registration information allows sar agencies start rescue more quickly. example, if shipboard telephone number listed in registration unreachable, assumed real distress event occurring. conversely, information provides quick , easy way sar agencies check , eliminate false alarms (potentially sparing beacon s owner significant false alert fines.)

an unregistered 406 beacon still carries information, such manufacturer , serial number of beacon, , in cases, mmsi or aircraft tail number/icao 24-bit address. despite clear benefits of registration, unregistered 406 beacon substantially better 121.5/243.0 beacon; because hex code received 406 beacon confirms authenticity of signal real sar alert.

beacons operating on 121.5 , 243.0 mhz transmit anonymous siren tone, , carry no information sar agencies. such beacons rely solely on terrestrial or aeronautical monitoring of frequency. in uk, distress , diversion cell of royal air force provides continuous monitoring of 121.5 , 243.0 mhz, autotriangulation network of terrestrial receivers on both frequencies. in canada, air traffic service stations (control towers or flight service facilities) monitor 121.5 mhz during operating hours. overflying commercial or private aircraft monitor 121.5 mhz if equipped suitable receiver, , if time/courtesy permits; monitoring 121.5 mhz not mandatory. sar authorities have no way of knowing whether 121.5/243.0 mhz signal sar signal until physically deploy location , home in on source (and sound) of transmission. since sar resources scarce (and expensive), countries not deploy useful sar homing assets (aircraft) until ambiguity has been resolved (see doppler).

operational testing

according u.s. federal aviation administration, ground testing of a-, b-, , s-type elts done within first 5 minutes of each hour. testing restricted 3 audio sweeps. type , ii devices (those transmitting @ 406 mhz) have self test function , must not activated except in actual emergency.

the united states coast guard web page epirbs states: may fined false activation of unregistered epirb. u.s. coast guard routinely refers cases involving non-distress activation of epirb (e.g., hoax, through gross negligence, carelessness or improper storage , handling) federal communications commission. fcc prosecute cases based upon evidence provided coast guard, , issue warning letters or notices of apparent liability fines $10,000.