Well we all must be aware of the EPIRB that is Emergency Position Indicating Radio Beacon is small, self contained, battery operated radio transmitter which is watertight and buoyant. EPIRB is a device which provides distress alert and location information to search and rescue services (SAR) for aviation, maritime and land users in case of an vessel is in Distress situation. Now before we proceed further with COSPAS-SARSAT EPIRB, let us first understand the purpose of EPIRB.
Purpose of EPIRB
- To determine the position of a mobile unit / survival craft or survivors during SAR operations.
- It is a secondary means of ship to shore Distress Alerting.
EPIRB signal indicates that one or more persons are in Distress, may no longer be on board a ship or aircraft and that receiving facilities may not be available (except by means of GMDSS hand held VHF sets).
COSPAS - SARSAT EPIRB
COSPAS SARSAT is a joint international satellite-aided search and rescue system, established by organisations in Canada, France, Russia and the United States, which now has over 30 countries and organisations contributing to the operation and management of the system.
The objective of this system is accomplished through the use of four LEOSAR (Low earth Orbit) Cospas-Sarsat satellites which receive the transmissions of radio-beacons operating on 406 and 121.5 Mhz and relays to Ground Stations (LUT's: Local User Terminals) on 1544.5 Mhz and GEOSAR (Geostationary Earth Orbit) satellites which receive the 406 Mhz transmission from beacons and relays the data to GEOLUT's. (Discussed later in the post)
The EPIRB signals are detected by COSPAS-SARSAT polar orbiting satellites (LEOSAR) at a distance of 1000 km from earth, equipped with suitable receivers/processors. Each Satellite makes a polar orbit of Earth in 100 Minutes. From any point on earth the satellite is in view for 15 minutes.
The signals received by the satellite are then relayed to a ground receiving station, termed a Local User Terminal (LUT), which processes the signals and calculates the position of the EPIRB using Doppler shift Principles (using relative motion of the satellite with respect to the EPIRB).
An alert is then sent to a Mission Control Centre which then contacts the appropriate MRCC of the SRR (Search and Rescue Region) in which the EPIRB is located to initiate SAR activities.
Types of EPIRB
- COSPAS-SARSAT EPIRB: These EPIRBs can be used in any Area.
- VHF EPIRB: Intended for use in Area A1 only.
Modes of Operation
There are two modes of operation for detection of a beacon:
1. Real Time Mode: In this mode the orbiting Satellite can see both, the EPIRB and LUT (in the footprint of the Satellite). In this mode a repeater on board the satellite relays the EPIRB signals directly to ground, where. it is received and processed by a LUT. Both frequencies 406 and 121.5 Mhz are used in this mode. The Satellite covers an area of approximately 2000 km either side of its track over ground.
2. Global Coverage Mode: In this mode the satellite can only see the EPIRB and not any LUT, that is LUT is not in the area of the satellite when EPIRB signals were received. The signals received from an activated EPIRB are tagged and stored in the satellite's memory.
Later as the satellite's orbit path brings it into view of LUT, information, including beacon ID, frequency and time of detection, is continuously relayed down to this LUT (and all subsequent LUT's in its path). The LUT after computing the position of the EPIRB, relays an alert through the Mission Control Centre to the appropriate SAR authority. For this mode only the 406 Mhz signal is used and the average response time in this mode is approximately 1 hour.
Geostationary Satellite Component
While the COSPAS SARSAT system provides global coverage, there is some time gap between passes as discussed earlier in modes of operation, which results in some delay in the detection of the signals from the beacon.
Having a geostationary satellite can help detect the signal almost on a real time basis. Considering this aspect, 406 Mhz payloads are now available on board five Geostationary Satellites provided by USA (GOES, MSG) and India (INSAT).
(GOES: Geostationary Orbiting Environmental Satellite, MSG: Meteorological Second Generation, INSAT: Indian National Satellite)
Almost as soon as beacon is activated in the GEOSAR satellite coverage area, it can be detected by the GEO-LUT. As there is no relative movement between a transmitting beacon and a satellite, it is not possible to use Doppler effect to calculate the beacon position. Location information may be provided by an external or internal navigation device, which is included in the digital message of a 406 Mhz beacon. This position data is sent with an alert message to the MCC for re-transmission to the appropriate Rescue Co-ordination Centre. Latest EPIRBs have a built in GPS and these are labeled G-EPRIB's
Identification of EPIRB
Every EPIRB has a unique identity code which is part of the digital signal transmitted. This could be either a Serial No. or MMSI No. This ID is programmed into the beacon by the supplier before it is installed onboard a vessel.
Theoretically MCCs anywhere in the world receiving a COSPAS SARSAT EPIRB signal can identify the vessel in distress and its country of registration. Therefore, it is imperative that EPIRB's are registered with the relevant authorities in the Flag State, so that details can be made available to SAR authorities when requested.
EPIRB operating Procedures
Operating procedures differ from one manufacturer to another manufacturer and between models and therefore it is always recommended to read Manufacturer's instructions before testing / operating.
Mostly now a days EPIRB are activated automatically or can be done Manually. Automatic activation happens when vessel is sinking. Due to ingress of water in the bracket / housing of EPIRB the HRU (Hydrostatic Release Unit) is activated and cuts lose the EPIRB which will then float in water activated.
Manual activation is done when vessel is in Distress and crew is abandoning the ship. The crew can then manually remove the EPRIB from the bracket / housing and activate it by one single switch activation, and abandon the vessel.
Once activated the EPIRB also gives an light indication to confirm if EPRIB is transmitting alert and Activated.
Once Activated the EPIRB operating life is 48 Hours. The 406 Mhz beacons transmit a 0.5 Second burst every 50 Seconds. The 406 Mhz beacon output power is 5 W while that of the 121.5 Mhz is 75 mW. SAR aircraft with specialised direction finding equipment are used to locate the EPIRB using the 121.5 Mhz beacon transmissions.
The VHF (Ch. 70) EPIRB is intended for the use in Area A1 only. When activated it transmits a DSC Distress alert on VHF Channel 70 (156.525 Mhz). All stations within VHF Range will receive this alert and EPRIB Emission will be indicated on the VHF DSC screens. Position will be indicated as no information.
Vessels should then immediately set watch to VHF RT Channel 16 and switch on their X Band (3 cm Radar) as every VHF EPIRB has an inbuilt SART for providing a locating signal.
EPIRB Performance Standards
The EPIRBs have to meet various performance standards such as:
- be capable of being easily activated by unskilled personnel.
- be fitted with adequate means to prevent accidental activation.
- Remain watertight after immersion in water (10 m) for 15 Minutes.
- be automatically activated after floating free
- be able to be activated / deactivated manually.
- have some means to indicate that signals are being transmitted.
- withstand being dropped from a height of 20 m into water without being damaged.
- be capable of being tested onboard, without radiating a distress alert signal.
- be of highly visible hello/orange colour and fitted with retro-reflective material.
- be equipped with a buoyant lanyard, used as a tether, this is to be arranged in such a way as to prevent it being trapped by ship's structure when floating free.
- have low duty cycle light activated by darkness to indicate its position to survivors / rescuers.
- be installed in an easily accessible position and clear of any observations.