EPIRBs - Part I
Taking the "Search" out of Search and Rescue!
Emergency Position Indicating Radio Beacons (EPIRBs) are either manually or automatically activated radio beacons that when used; transmit a digital signal that can be instantly picked up by satellites. With the latest changes in regulations, EPIRBs now transmit on 406 MHz, this frequency has been set aside as an international distress frequency. Today’s EPIRBs also transmit a low power signal on 121.5 MHz which allows search and rescue (SAR) teams to home in on the beacon’s position once they are in the area.
EPIRBs are used as a last resort safety device only; to be used when all else has failed and you are knee deep in whale doo doo. The latest version, the Category I and Category II Satellite 406 EPIRBs with built in GPS will provide position information to SAR teams that effectively takes the Search out of Search and Rescue.
How EPIRBs Work
When activated, the latest version of EPIRBs transmit a coded digital signal with information about the vessel in distress. This signal is then picked up by the COSPAS-SARSAT system. This system is made up two different types of satellite constellations: 1. (GEOSAR) - Geostationary Earth Orbiting Search and Rescue satellites and 2. (LEOSAR) - Low Earth Orbiting Search and Rescue satellites.
Once an EPIRB is activated the signal is almost instantaneously detected by the GEOSAR satellites and an alert is sent to the Mission Control Center via Local User Terminals. The only downside to this is that due to orbital mechanics, the GEOSAR system is unable to provide the data necessary to provide location information. So, unless you are lucky enough to have an EPIRB with integrated GPS, they know you are in trouble, they just don’t know where you are - YET!
This is where the LEOSAR satellites come into play. When a LEOSAR satellite makes a pass overhead it not only receives the same information as the GEOSAR system, it also has the ability to provide doppler processing of the EPIRB signal to determine your location. This information is then then sent to the Mission Control Center where the signal is processed and a location is calculated.
The number of COSPAS and SARSAT LEOSAR satellites allows global coverage capabilities of typically less than 1 hour.
Once a position has been calculated, this information is then passed to the appropriate Rescue Coordination Center who directly or indirectly provides for the allocation of assets required to provide for search and rescue.
What Types are available?
Satellite 406 MHz EPIRBs are divided into 2 categories:
1. Category I EPIRBs can be activated manually or automatically. They are stored in a hydrostatic release bracket designed to allow the unit to float free. In the event that the vessel sinks the Category I EPIRB is typically released at a depth of 3 to 13 feet where it then floats to the surface. A wet switch then activates the unit and it begins transmitting. Additionally the unit can be activated manually by flipping a switch.
2. Category II EPIRBs are not designed to float free and must be removed from their brackets manually. Once removed they may be activated by flipping a switch or they will also activate automatically when wet.
Additionally many Category I and II EPIRBs can be purchased with a GPS interface that allows the vessel’s onboard navigation system to update the EPIRBs position information so that the last known position is transmitted in the digital distress signal.
Finally at the top of the heap are the Category I and II EPIRBs that have integrated GPS units built in. These units will constantly transmit the beacons position to SAR units and likely bring a faster response.