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COSPAS-SARSAT SEARCH AND RESCUE SYSTEM—TAKING THE "SEARCH" OUT OF
"SEARCH AND RESCUE"

Rescue at sea February 1, 2002 — NOAA operates a series of low Earth and geostationary orbiting 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—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, U.S. Air Force and NASA. Since the inception of the system in 1982, more than 13,000 lives have been rescued worldwide and more than 4,500 lives have been rescued just in the United States.

How it Works
The Cospas-Sarsat system consists of emergency radio beacons, equipment on satellites in low-Earth and geosynchronous orbits, ground receiving stations—also called Local User Terminals, Mission Control Centers, and Rescue Coordination Centers. In general, emergency beacons are used to transmit distress signals to the satellites on either 121.5, 243 or 406 MHz frequencies. 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:

Sarsat system diagram

  1. People in Distress: To make use of the Cospas-Sarsat system—mariners, aviators and land users in distress simply need to activate an emergency distress beacon, which is compatible with the Cospas-Sarsat system.

  2. SARSAT-COSPAS Satellites: The emergency signal is received by the Cospas-Sarsat satellites and relayed to a ground receiving station.

  3. Ground Receiving Stations (Local User Terminals): The ground station, also known as a Local User Terminal, 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 beacons signals detected by polar orbiting satellites, the position of the distress beacon is computed using Doppler technology (directional information calculated based on the relative motion between the satellite and the emergency beacon). In the case of 406 MHz beacon signals detected by geostationary satellites, however, 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 fourteen LUTs in seven locations. Specifically, there are two LUTs in each of the following locations: Suitland, Md.; Houston, Texas; Vandenberg AFB, Calif.; Fairbanks, Alaska; Wahiawa, Hawaii; Puerto Rico; and Guam. There are currently 38 LUTs in operation worldwide with several more being built each year.

  4. U.S. Mission Control Center: The U.S. Mission Control Center at the NOAA facility 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), 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, then the alert is transmitted to that country's MCC. This is possible due to the fact that all Cospas-Sarsat MCCs are interconnected through nodal MCCs that handle data distribution in a particular region of the world. Currently, there are 24 MCCs in the world (five of which are nodal MCCs operated by the United States, France, Russia, Japan and Australia). The operation is manned 24 hours a day, 365 days a year. However, the vast majority of alert data distribution is handled automatically.

  5. Rescue Coordination Center: The Rescue Coordination Center then begins the actual search and rescue operation. RCCs for incidents at sea and on land in the United States are operated by the U.S. Coast Guard and Air Force, respectively. 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 alert, it dispatches Search and Rescue teams to locate the vessel in distress. In the case of 121.5 MHz beacons (which cannot be registered with NOAA), however, each distress call (whether real or false) 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, make sure you test your beacon and follow the manufacturer's recommendations carefully. Also, make certain that you register all 406 MHz beacons with NOAA.

  6. Search and Rescue Forces: Search and rescue forces are sent out by either the U.S. Air Force, the U.S. Coast Guard or local SAR personnel depending on where the emergency signal is originating from (i.e., air, water or land, respectively). 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. Based on this information alone, search planning can begin. Ideally, however, a Cospas-Sarsat polar satellite will overfly the beacon within the next 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. [Note, however, that the 406 MHz beacons detected by geostationary satellites are not able to be located using Doppler shift because geostationary satellites have no relative motion between them and the emergency beacons. They can, however, provide immediate alerts and can 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 NOAA 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. Once a polar orbiting satellite flies over the beacon, its exact location can be calculated using Doppler shift. This information can then be forwarded to the SAR personnel who may already be en route.]
Satellites
NOAA operates Earth-observing (i.e., both polar orbiting and geostationary) satellites that are used to make accurate environmental and weather observations. Each satellite also carries Search and Rescue Satellite-Aided Tracking payloads that can detect and locate emergency beacons activated by people in distress:

  • Polar Orbiting Satellites: 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) as they orbit the globe. Antennas 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 in 30-45 minutes with even quicker passes near the poles. Although the emergency information is not relayed immediately by these satellites, they can convey accurate location information via Doppler shift (directional information calculated based on the relative motion between the satellite and the emergency beacon)

  • Geostationary Satellites: Geostationary Operational Environmental Satellites orbit at about 36,000 km (22,320 miles) above the Earth's equator and most recognized as the dramatic images often seen on television weather broadcasts. From their vantage point high above the equator, GOES can see large portions (i.e., 85 percent) of the Earth continuously. GOES satellites can only detect 406 MHz emergency beacons and because they are geostationary (i.e., have no relative motion between them and the emergency beacons) they cannot use Doppler shift processing to locate emergency signals (although more advanced 406 MHz beacons often have GPS capacity, which can provide their position). They can, however, relay 406 MHz signals to ground stations immediately after a beacon is activated. Furthermore, if the beacon was previously registered with NOAA, a RCC can use this information to try to locate the vessel, aircraft or individual and determine the nature of the distress. This allows them to mobilize SAR resources while waiting for a polar orbiting satellite to get a better fix on the beacons location (using Doppler shift).

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 for maritime applications, 2) Emergency Locator Transmitters for aviation applications, and 3) Personal Locator Beacons for individuals in distress. There are two types of EPIRBs and ELTs. 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 ELTs that are normally triggered by the impact of a crash. Ships carry floating EPIRBs that are activated by immersion in water. Both can also be activated manually (also note that PLBs can only be activated manually). PLBs have been used by the State of Alaska since 1994 to help protect people from the hazards of the Arctic. When activated, an Alaska PLB transmits a digitally coded signal on the 406 MHz frequency. This signal is received by a Cospas-Sarsat satellite and relayed to a ground station. The ground station calculates the PLB location and transmits the information to the U.S. Mission Control Center. The USMCC recognizes these specially coded beacons as Alaska PLBs and transmits a distress message directly to the Alaska Rescue Coordination Center in Anchorage, which is operated by the Alaska Air National Guard and the Alaska State Troopers. The AKRCC then use state, local, or federal assets to conduct the rescue. To date, this special program has helped save more than 200 lives.

Frequencies
Emergency beacons (i.e., EPIRBs and ELTs) transmit on a radio frequency of 121.5 MHz and 406.025 MHz, however, there are important differences between the two frequencies (note that PLBs also transmit on 121 although most transmit on 406):

  • 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 digital information contained in a registered data base. This database can supply the beacon type, its country of origin, 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: The Cospas-Sarsat satellites 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 250,000 406 MHz beacons presently in use worldwide (of those, more than 78,000 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
121.5 MHz beacons, which sell for about $200-$1000 a piece, will no longer be detected by satellites starting in 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. While both the 121.5 and 406 MHz beacons transmit distress alerts via satellite, the two types are otherwise totally different. On the one hand, 406 beacons emit powerful positionally accurate, satellite-compatible digital "locator" signals, each with an encoded "fingerprint," on a frequency that's reserved exclusively for their use by international law. 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 406's registration cards (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. But pure 121.5 beacons are another story. They emit comparatively weak, inaccurate analog locator signals that are both confusing to satellites and totally anonymous. Since it cannot accommodate registration information, the potential distress cannot be checked by phone. Combine this with the fact that 121.5 beacons use an indiscrete "party-line" frequency shared with scads of interference and anomaly-generated electrical devices (ranging from home appliances to military radars), and you get a staggering number of false alerts, many of which must be dealt with on site. In fact, people are at risk each year because of the failures of the 121.5 system. What this means is that the majority of these alerts have to be ignored, at least until a third or forth satellite pass confirmation (a slow process that delays legitimate rescues by up to six critical hours).

Future Developments
The newest technology for Cospas-Sarsat is 406 MHz emergency beacons that digitally transmit their identification and position. These beacons utilize either an external or internal electronic navigation receiver (i.e., Global Positioning System) and can transmit their position down to 100 m 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 prior to 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.

Relevant Web Sites
Recent Rescues

HISTORY OF THE SARSAT SYSTEM

Sarsat Satellites

EMERGENCY POSITION INDICATING RADIO BEACONS(EPIRBs), EMERGENCY LOCATOR TRANSMITTERS (ELTs), and PERSONAL LOCATOR BEACONS (PLBs)

ALASKA PLB PROGRAM

ONLY YOU CAN PREVENT FALSE ALARMS

BEACON REGISTRATION FORMS

FREQUENTLY ASKED QUESTIONS

SARSAT PROGRAM & SYSTEM DOCUMENTATION

SARSAT SLIDE PRESENTATIONS

Media Contacts:
Patricia Viets, NOAA Satellite Service, (301) 457-5005