OUT OF SEARCH &
FROM THE BOATU.S. FOUNDATION FOR BOATING SAFETY & CLEAN WATER
4.5-square-mile search zone.
The other satellite system at work is the
Geostationary Orbiting Search and Rescue
(GEOSAR), whose satellites orbit with the
Earth and remain in fixed positions over it.
As long as you’re between about 70 degrees
N and 70 degrees S, these satellites receive
your beacon’s information and transmit it to
a ground terminal almost instantaneously.
They can’t calculate a position using Doppler
shift, however, because they’re not moving.
The only way they can provide your position information is if your emergency signal
includes your GPS position.
YOUR BEACON MATTERS
Older beacons – and many models still sold
today – are unable to transmit a vessel’s GPS
coordinates, leaving the Doppler shift as the
only way to determine a position. Instead of
two hours and a position accurate to a bit
Connecting to a constellation of satellites and rescue assets,
today’s modern, highly accurate GPS-equipped EPIRBs and PLBs
could be your lifesaver in an emergency. Here’s how they work
BY TOM NEALE
TODAY’S GPS-equipped Personal Locator Beacons (PLBs) and Emergency Position Indicating Radio Beacons (EPIRBs) are accu- rate, fast, and portable. Since 1982, EPIRBs and PLBs have helped to save more than 35,000 lives around the world. That’s how rescue can work today, with the right equipment and the right information.
Here’s how a modern GPS-equipped emergency beacon reduces search time.
Once activated (see “What You Need To Know”), an EPIRB or PLB broadcasts a
406-MHz message, with your vessel’s unique identification code, to two different satellite
systems. The first, and original, array is the Low Earth-Orbiting Search And Rescue (LEOSAR)
system, which can detect and locate 406-MHz alerts worldwide as its satellites pass over
the Earth’s surface. The satellite’s equipment also transmits your information to special
land-based terminals as soon as it comes within range (around 2,500 miles). Even if your
emergency beacon does not transmit your GPS position, these satellites, in conjunction with
their terminals on land, can determine your location by measuring the Doppler shift of your
signal (see “Frequently Asked Questions”). The initial Doppler shift position can be off by
many miles, but with each pass of the satellite over your distress signal, about once every
100 minutes, your position is refined. Obtaining a reliable position for a distressed vessel can
take two hours or more, and that position is only accurate to a mile or more, resulting in a