Cospas-Sarsat: Saving Lives for 20
Years
by NOAA
Reprinted with permission of FAA Aviation News
Thanks to the
international humanitarian program known as Cospas-Sarsat, which
celebrated its 20th anniversary in October 2002, more than
14,000 lives have been saved worldwide, including about 5,000 in the
United States, since the program began in 1982. Cospas-Sarsat is a
search and rescue system that uses U.S. and Russian satellites to
detect and locate emergency beacons carried by aircraft, ships, or
individuals in distress. Last year, 166 lives were saved: 112 on the
seas, 39 in the Alaskan wilderness, and 15 on downed aircraft in the
states around the country.
The National Oceanic
and Atmospheric Administration (NOAA) operates a series of
polar-orbiting and geostationary environmental satellites that detect
and locate aviators, mariners, and land-based users in distress. These
satellites, along with a network of ground stations and the U.S.
Mission Control Center in Suitland, MD, are part of the International
Cospas-Sarsat program, whose mission is to relay distress signals to
the international search and rescue community.
Sponsored by Canada,
France, Russia, and the United States, and started during the Cold
War, the system operates 24 hours a day, 365 days a year, and aims to
reduce the time required to alert rescue authorities whenever a
distress situation occurs. In the United States, the Cospas-Sarsat
program is operated and funded by NOAA, the U.S. Coast Guard, the U.S.
Air Force and the National Aeronautics and Space Administration
(NASA).
'We are an
international humanitarian program whose goals and rewards are the
same'saving
lives,' say Ajay Mehta, manager of NOAA's Sarsat program. 'We had an
unusual rescue last year with a bear circling a private plane that had
crashed in Alaska with two people on board,' said Mehta. 'These folks
were in a dangerous predicament. Yet, because there was an emergency
locator transmitter on board the aircraft that activated upon impact,
rescue authorities were able to respond to the distress quickly. On
arrival, the search and rescue aircraft saw the situation unfolding
and dispatched a helicopter to retrieve the occupants and bring them
to safety."
How It Works
The Cospas-Sarsat system consists of emergency radio beacons carried
on aircraft and ships, equipment on satellites, ground receiving
stations (also called Local User Terminals), Mission Control Centers,
and Rescue Coordination Centers. When an aircraft, ship, or person is
in distress, an emergency beacon is activated. These beacons transmit
distress signals to the satellites either on the 121.5, 243, or 406
MHz frequencies. In the case of aircraft, the beacons are well known
by pilots as Emergency Locator Transmitters, or ELT. Ground stations
track satellites in the Cospas-Sarsat constellation and process the
distress signals. The processed information is then forwarded to a
Mission Control Center where it's combined with other information and
passed to search and rescue authorities.
The ground station
receives the emergency signal and calculates the location of the
signal by one of two methods. In the case of 121.5 and 406 MHz signals
detected by polar orbiting satellites, the position of the distress
beacon is computed using Doppler technology (the relative motion
between the satellite and the emergency beacon). In the case of 406
MHz signals detected by geostationary satellites, only those beacons
equipped with GPS capabilities can be accurately located. This
position can then be transmitted as part of the distress signal to a
mission control center. In the United States, NOAA operates 14 Local
User Terminals (LUT) in seven locations. There are two LUT in each of
the following locations: Suitland, MD; Houston, TX; Vandenberg AFB,
CA; Fairbanks, AK; Wahiawa, HI; San Juan, Puerto Rico; and Andersen
AFB, Guam. There are currently 39 LUT in operation worldwide with
several more being built each year.
The U.S. Mission Control Center (USMCC) in Suitland,
MD, obtains the location information from the ground receiving
stations. The USMCC combines this information with other satellite
receptions (from other ground stations and MCC), further refines the
location and generates an alert message. This alert is then
transmitted to the appropriate Rescue Coordination Center based on the
beacon's geographic location and/or identification. If the location of
the beacon is in another country's service area, the alert is
transmitted to that country's MCC. This is possible because all
Cospas-Sarsat MCC are interconnected through nodal MCC that handle
data distribution in a particular region of the world. Currently,
there are 24 MCC worldwide (five of which are nodal MCC operated by
the United States, France, Russia, Japan, and Australia). Although the
operation is always manned, the vast majority of alert data
distribution is handled automatically.
Once the Rescue
Coordination Center is alerted, it begins the actual search and rescue
operation. In the United States, these rescue centers are operated by
the U.S. Coast Guard for incidents at sea and by the U.S. Air Force
for incidents on land. In the case of NOAA-registered 406 MHz beacons,
the RCC telephones the beacon's owner and/or emergency contact, and if
it cannot determine that the signal is a false alarm, it dispatches
search and rescue (SAR) teams to locate the aircraft or vessel in
distress.
In the case of 121.5 MHz
beacons, which cannot be registered with NOAA, each distress call,
whether real or a false alarm, must be tracked to the source using
direction-finding equipment. The manpower and cost of responding to
false alarms are extremely high. To avoid false alerts, NOAA
recommends that pilots be sure to use care when testing and
maintaining their ELT and follow the manufacturer's recommendations
carefully.
Search and rescue
forces are sent out either by the U.S. Air Force, the U.S. Coast Guard
or local SAR personnel depending on the origin of the emergency
signal. SAR forces include fixed wing aircraft, helicopters, ships,
boats, search parties, and sometimes commercial ships. The SAR forces
find the people in distress and bring them to safety. To focus the SAR
team's initial search, all 121.5 MHz and most 406 MHz beacons transmit
a second "homing" frequency of 121.5 MHz. Armed with radio detection
devices, the Coast Guard and other rescue authorities can track the
homing frequency and quickly locate the emergency beacon.
A Cospas-Sarsat
polar satellite will typically overfly a beacon within an hour and
calculate a Doppler-determined location. This process can locate
beacons within an accuracy of 5-12 miles for 121.5 MHz beacons and 1-3
miles for 406 MHz beacons. The 406 MHz beacons detected by
geostationary satellites provide immediate alerts. However, they are
not able to be located using the Doppler shift because these
satellites have no relative motion between them and the emergency
beacons. They can, however, be registered in NOAA's beacon database.
Thus, if the 406 MHz beacon has been registered, the SAR team can
begin its initial verification of the alert using the information
contained in NOAA's beacon registration database.
Often this detective
work yields a general location of the vessel or aircraft in distress
and SAR assets can be readied or dispatched to that general area.
Then, when a polar orbiting satellite flies over the beacon, its exact
location can be calculated using the Doppler shift and the location
forwarded to the SAR personnel who may already be en route.
Satellites
NOAA operates both polar-orbiting and geostationary environmental
satellites that are used primarily for environmental applications.
Each satellite also carries Search and Rescue Satellite-Aided Tracking
(Sarsat) payloads that can detect and locate emergency beacons
activated by people in distress
NOAA's Polar
Orbiting Environmental Satellites circle the earth every 102 minutes
at an altitude of about 850 km (526 miles). The Russian Cospas polar
satellites circle the Earth every 105 minutes at an altitude of about
1,000 km (620 miles). Anten'nas aboard the satellites detect both 406
and 121.5 MHz emergency beacon signals and relay them to ground
stations. Since the satellites overfly the poles on every orbit,
coverage is best there and least at the equator. In the mid-latitudes,
the average waiting time for a satellite pass is 30-45 minutes, with
quicker passes near the poles.
NOAA's Geostationary
Operational Environmental Satellites orbit at about 36,000 km (22,320
miles) above the Earth's equator. From this vantage point, GOES can
see large portions of the Earth continuously. GOES satellites can
detect only 406 MHz emergency beacons. The more advanced 406 MHz
beacons often have GPS capacity, which can provide their position.
GOES satellites relay 406 MHz signals to ground stations immediately
after a beacon is activated.
Types of Beacons
Emergency beacons are powered by batteries and come in a variety of
shapes and sizes. There are three types of emergency beacons: 1)
Emergency Position Indicating Radio Beacons (EPIRB) for maritime
applications, 2) Emergency Locator Transmitters (ELT) for aviation
applications, and 3) Personal Locator Beacons (PLT) for individuals in
distress. There are two types of EPIRB and ELT. One type transmits an
analog signal on 121.5 MHz. The other type transmits a digital
identification code on 406 MHz and a low-power "homing" signal on
121.5 MHz. Aircraft carry ELT that are normally triggered by the
impact of a crash. Ships carry floating EPIRB that are activated by
immersion in water. Both can also be activated manually. PLB have been
used by the State of Alaska since 1994 to help protect people from the
hazards of the Arctic. Although PLB are not yet authorized for general
use, the Federal Communications Commission is currently considering
rule making to allow use of PLB anywhere in the United States starting
in 2003.
Frequencies
Emergency beacons transmit on a radio frequency of 121.5 MHz and
406.025 MHz. There are several important differences between the two
frequencies:
-
Accuracy:
The 406 MHz frequency provides the location of people in distress
with an accuracy of about 2-5 km (1-3 miles). The 121.5 MHz
frequency provides the location of emergency beacons with an
accuracy of about 10-25 km (5-12 miles).
-
Digital vs. Analog:
The 406 MHz signal is digital and can be stored aboard the
spacecraft for later relay to the next available ground station
(giving it a global capacity). The 121.5 MHz signal is analog and is
not stored aboard the spacecraft, thus providing only a regional
capability.
-
Data Encoding Capabilities:
The 406 MHz distress beacons can transmit a unique, pre-coded
message, which links it to information contained in a registered
database. This database can supply the beacon type, its country of
origin, emergency points of contact, and the registration number of
the maritime vessel or aircraft. The registration information helps
the search and rescue forces identify the vessel or aircraft in
distress and greatly speeds up response. 121.5 MHz beacons are not
capable of data encoding.
-
Detection Capacity:
Satellites in the system are designed for global reception of 406
MHz beacons. 121.5 MHz beacons can also be detected, but only if a
satellite is within range of the beacon and the ground station
simultaneously. The 121.5 MHz signal was originally designed for
alerting overflying aircraft and is excellent for use as a homing
signal. However, because most 406 MHz signals are not suitable for
homing, many 406 MHz beacons also transmit a 121.5 MHz homing signal
(some 406 MHz beacons also have GPS capabilities to further assist
in locating distress beacons).
-
Number:
There are approximately 285,000 406 MHz beacons currently in use
worldwide. Of those, more than 87,000 have been registered in NOAA's
beacon database. There are approximately 590,000 121.5 MHz beacons
in use worldwide, primarily on small aircraft.
Phase-Out of 121.5
MHz Satellite Alerting
The 121.5 MHz beacons, which sell for about $200-$1000 each, will no
longer be detected by satellites starting on February 1, 2009. Owners
will have to replace them with a more sophisticated type of unit, the
406 MHz beacon, which sells for $500-$2,500 depending on features and
application. "The 406 beacons emit a powerful, satellite-compatible
digital signal, with an encoded "fingerprint," on a frequency that's
reserved exclusively for their use by international regulation," Mehta
said. Although they also simultaneously emit a short range 121.5
signal when activated, it is merely a "homer," a steady, localized
radio beep that rescuers can use to home' in on victims once an
accident site has been located. "Combine this double-barreled
locator/homer capability with the registration information available
for 406 beacons'a search-assisting database containing a beacon's
information and emergency phone numbers that can be checked prior to
launching expensive rescue efforts, but more importantly provide
information that can help save the user's life'and you have an
accurate, cost-effective SAR tool," Mehta said.
Comparatively, 121.5
beacons emit weak, inaccurate analog signals that are both confusing
to satellites and anonymous, as they cannot accommodate registration
information. The 121.5 beacons use a frequency that can be very
crowded and have many devices operating around it that can appear as
distress alerts. Examples of interfering signals in the 121.5 MHz band
include stadium scoreboards, pizza ovens, and automatic teller
machines. This results in a staggering number of false alerts, many of
which must be dealt with on site. The majority of these alerts have to
be ignored, at least until a third or fourth satellite pass
confirmation. This is a slow process that can delay other rescues by
up to six hours.
Future Developments
The newest technology for Cospas-Sarsat is 406 MHz emergency beacons
that digitally transmit their identification and position. These
beacons use either an external or internal navigation receiver (i.e.,
Global Positioning System) and can transmit their position down to
100-meter accuracy. This allows geostationary satellites to combine
immediate alerts with precise locations. The polar orbiting satellites
are also capable of receiving these signals, thereby providing global
coverage.
Conclusion
The Cospas-Sarsat system provides a tremendous resource for protecting
the lives of aviators and mariners that was unthinkable before the
Space Age. With a 406 MHz beacon, rescue forces can be quickly
summoned from anywhere on Earth' 24 hours a day, 365 days a week. "The
number of people rescued continues to rise internationally as more
countries and people sign on to use the advantages and benefits of the
Cospas-Sarsat system," said Mehta.
To learn more
about NOAA's role in the Cospas-Sarsat program visit
http://www.sarsat.noaa.gov/.
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