The 1974 International Convention for the Safety of Life at Sea (SOLAS) and 1979 International Convention on Maritime Search and Rescue called for the development of a global search and rescue (SAR) plan and a Global Maritime Distress and Safety System (GMDSS) to provide the space-based and terrestrial communications needed to support the worldwide search and rescue plan.

The Coast Guard’s National Distress and Response System (NDRS), which was established in the 1970s, required faster and improved direction-finding and reduction of coverage gaps. In 2001, the Coast Guard began upgrading its existing radiotelephone coverage with the National Distress and Response System Modernization Program with a Phase 1 contract. Rescue 21 Coastal (R21-C) is a Department of Homeland Security (DHS) U.S. Coast Guard system designed to deliver the primary mission of SAR. The system comprises an advanced command and control, digital and analog VHF and UHF communications system that uses direction-finding (DF) technology to accurately locate the source of maritime distress calls through the use of multiple simultaneous communications channels.

Today, in compliance with the 1974 SOLAS, the Coast Guard’s Rescue 21 system provides reliable, secure, nationwide communications coverage for “Sea Area A1,” an area within the radiotelephone coverage of at least one VHF coast station in which DSC (digital selective calling – Channel 70) alerting and radiotelephony services are available, as defined by the International Maritime Organization.

 

The Coast Guard’s Sea Area A1 coverage represents more than 90 percent of the area within 20 nautical miles seaward of the territorial baseline along the East, West, Great Lakes and Gulf coasts of the United States, excluding Alaska, and including Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States, and the Northern Mariana Islands of Saipan, Tinian, and Rota. That’s more than 296,000 square nautical miles of U.S. coastline.

The Coast Guard selected General Dynamics Mission Systems (GDMS) to provide a turnkey solution. GDMS has been responsible for system design, manufacture, pre-installation planning, installation, lifecycle maintenance, and training. The GDMS system includes 258 unmanned remote coastline communication tower sites linked through backhaul networks to 34 sector command centers (SCCs) and 160 Coast Guard Watch Stations. The system requirement is to receive VHF signals up to 20 nautical miles from the coast.

Each unmanned remote coastline communication tower site consists of an electronics shelter containing up to six Land Marine Radio (LMR) base stations with UHF, VHF, and DF antennas on the tower. At least one of the LMR base stations is always tuned to monitor the international distress Channel 16, while a second LMR base station is always tuned to monitor the internal distress data Channel 70. The remaining LMR base stations are used by the Coast Guard to support its command and control communications with its marine and air assets.

The first SAR case using Rescue 21’s advanced capabilities took place on Nov. 13, 2005, in Coast Guard Sector Baltimore, one of the first sectors to receive the system. By 2015, the Rescue 21 system was installed on both coasts and the Great Lakes of the contiguous United States and three island regions: Puerto Rico, Hawaii, and Guam. Deployment in the Alaska and the Western Rivers region of the United States was completed in June 2017.

 

MORE THAN A “MAYDAY!”

While you can still hear someone calling for help on the radio, Rescue 21 is much more than a “Mayday!” alert system.

After getting a DSC-enabled marine radio, boaters can register their transceivers and get a Maritime Mobile Service Identity (MMSI) number, a unique nine-digit number that is assigned to a DSC radio or an AIS (Automated Identification System) unit on larger commercial ships. Similar to a cell phone number, an MMSI number is a unique calling number for DSC radios or an AIS unit. Boaters can obtain their MMSI from organizations like BoatUS or the United States Power Squadrons. Radio owners can provide contact information about both themselves and their boats. Thanks to the MMSI number embedded in any messaging, the Coast Guard can access the information in the national distress database for use in emergency situations, and when boaters connect their device to their GPS system, any call automatically includes a GPS location.

 

The MMSI is specific to a vessel and user. If a boater sells either the boat or the radio, the MMSI registration must be cancelled and a new one established for the new owner. This is necessary to ensure that the Coast Guard is able to contact the right persons if a distress situation were ever to occur.

According to the Coast Guard Navigation Center, “Take the time to interconnect your GPS and DSC-equipped radio. Doing so may save your life in a distress situation! Before interconnecting your radio and GPS, consult the owner’s manuals.”

When a mariner communicates over VHF Channel 16, the tower receives the voice transmission, such as the familiar “Mayday, Mayday.” The DF antenna on the tower also picks up the direction from which the transmission came, producing a line of bearing (LOB). The voice and data are then processed within the electronics shelter and the information is sent across the Coast Guard network to the SCC, where the voice and data are presented to the watch standers. The remote shelters are placed strategically, so that there is overlap in coverage. Multiple remote shelter sites may pick up the voice and distress data transmission, and the Rescue 21 software calculates a “fix,” telling the watch stander the latitude and longitude location of the source of the transmission in the water. With this information, the SCC can then perform a SAR mission using its marine and air assets.

The system can pick up a 1-second Channel 16 voice distress channel signal sent from a 1-watt transmitter located 2 meters above sea level and up to 20 nautical miles out, and provide a precise location to a watch stander at a Coast Guard SCC. With most calls, there are at least two remote towers that pick up the call, so there are at least two LOBs that can be triangulated to generate a“fix” out in the water.

DSC radios automatically retransmit any emergency signals, so other boats with a VHF-DSC radio could help relay a distress call without operator intervention. The position is encoded information within the DSC call, converted into internet data and sent via data lines.

Distress calls are received at the SCC, which has visibility of all of the towers within the sector’s area of responsibility (AOR).

 

“The magic happens in the command center,” said Lt. Shawn Antonelli, an operations center watchstander at Coast Guard District 7 in Miami.

Each sector has a communications unit specialist on watch in the SCC with a suite of radios and visibility to any activity detected at any of the towers within their AOR. For example, Sector St. Petersburg, near Tampa on Florida’s west coast, monitors eight towers. Any distress call within the sector would presumably be picked up by several of these towers, providing a precise location.

Every watch relief does tower-to-tower checks to make sure the system is working as a network and correctly relaying any signals or traffic. Since the towers are in known positions, the system can calibrate itself to make sure it’s accurate.

“If anything is off, we contact the GDMS support team, and they immediately check both hardware and software, and correct any errors or restore any equipment,” Antonelli said.

Some of the Rescue 21 towers have 360-degree coverage, while some have coverage areas blanked out by the tower, although there is usually complete coverage to seaward.

If the Rescue 21 tower receives an analog message but an LOB is not produced, the SCC can perform rangering analysis to determine a general search area for where the call may have originated. “Range ring analysis is used when the DF equipment is unable to produce an LOB. If an LOB is produced, our SAR assets will search the entire line of bearing within 2 degrees of each side,” said Antonelli.

 

Sadly, much of time, the general boating public does not register their information, so much of the benefit of having the DSC-capable radios is not available to the user. But, even if a distress call is sent by radio as a voice-only message, it can be triangulated by several towers.

“If we receive a distress call, we’ll try to contact the mariner first,” Antonelli said. “Then we’ll let everyone in the area know we have somebody in distress by transmitting an urgent marine information broadcast [UMIB]. We’ll provide the location of where the distress call came from, and ask others in the area to assist. In the meantime, we’ll get a rescue helicopter ready, and if necessary, it can launch within 30 minutes of the initial distress call.”
Antonelli said the playback capability can provide a lot of clues. “We can manipulate the audio to slow it down, or filter out interference or static. We can publish the audio on our intranet so other sectors can listen to the audio, as well.”

 

HOAX CALLS HURT EVERYONE

The Rescue 21 plotting capability can show if a fake mayday call is coming from land, even to the exact location of the boat parked in the driveway of the hoax caller. It can even be used as evidence in the felony prosecution of hoax callers.

Some ghost hoaxers become well known, and see it as a game of hide-and-seek, or catch-me-if-you-can.

“We have an entire file of a ghost hoaxer, sending the same message with the same voice. Others go to great lengths to stage their calls and fool the Coast Guard. One case in New York involved a theatrical actor who called in a yacht on fire with bodies in the water, complete with screaming voices and sound effects.”

 

The Coast Guard spent millions of dollars for the unsuccessful search, and months investigating the case. Four months later, the ghost hoaxer did it again.

The FCC, which owns the frequencies, gets involved. It’s a federal offense with significant fines and serious jail time involved.

 

AUTOMATED CORRELATION

“Before Rescue 21, the Coast Guard relied on the SCC operators to discern where the distress call was coming from based on what they could hear from the voice audio itself and manually plotting this information on physical maps. There was no automated correlation of voice and LOB information to calculate a fix,” said Forrest Holemon, technical manager, General Dynamics Mission Systems.“Today, Rescue 21 is a state-of-the-art capability and the only system that integrates the radio dispatch functionality with the DF LOB correlation function to automate the geolocation of distressed mariners.Correlating the voice transmissions with precise DF LOB locations takes the ‘search’ out of search and rescue,” Holemon said. “Technology has made this happen.”

Rescue 21 not only supports the Coast Guard’s command, control, and communications needs, but also seamlessly integrates with other government agencies at the federal, state, and local level.

According to Jeannie Zehring, program manager,General Dynamics Mission Systems has been able to keep the system technologically refreshed through numerous IT upgrades over the past 15 years, as well as meeting and exceeding the constantly changing cybersecurity requirements. “Working shoulder to shoulder, GeneralDynamics and the Coast Guard have accomplished all of the changes and updates without interrupting the service, so Rescue 21 can be constantly vigilant to perform its lifesaving mission,” Zehring said.

According to a Coast Guard statement, “Rescue 21 has played a vital role in prosecuting more than 75,000 search and rescue cases, and has been credited with saving thousands of lives in the process.”

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This article originally appears in Coast Guard OUTLOOK 2020-2021 Edition.