Search and rescue radar Transponders (SARTs) are the main means in the GMDSS for locating ships in distress or their survival craft, and their carriage on board ships is mandatory. The SART is a small, battery powered, omni–directional radar receiver and transmitter. They may also be incorporated into a float–free satellite EPIRB. The batteries fitted to a SART allow operation in the standby condition for at least 96 h, plus a further 8 h whilst being interrogated.
A SART operates in the 9 GHz (3 cm or ‘X-band’) radar frequency band and, on receiving a signal from a ship or aircraft radar, transmits a series of response (homing) signals. The SART can be activated manually or automatically (in some cases) so that it will thereafter respond when interrogated. The method of using and activating SARTs varies over the type available, but instructions are marked on the sides of all SARTs.
These response signals will be seen on the ship or aircraft radar screen as a line of 12 dots (0.64 n miles apart) extending approximately 8 n miles outward from the SART’s position along its line of bearing. This unique radar signal is easily recognised and allows the rescue vessel or aircraft to locate the survival craft. As the SART becomes closer, another 12 dots are produced, also 0.64 n miles apart (see Section 11.1.4).
A SART will not respond to 3 GHz radar (also referred to as 10 cm or ‘S-band’) radar.
On activation the SART will provide a visible and/or audible indication of its correct operation. It will also provide an indication when it is being interrogated by radar signals from a searching ship or aircraft.
A SART should respond when interrogated by a shipborne X-band radar with a scanner height of 15 m within 8 n miles. A SART should also respond when interrogated by a compatible X-band radar fitted to an aircraft operating at a height of 3 000 feet at a distance of at least 30 n miles.
AIS is included in the Safety of Life at Sea (SOLAS) Convention, and large ships began fitting AIS in July 2002. AIS transmits, automatically and at set intervals, dynamic information relating to the ship’s course, speed and heading; static information related to the ship’s name, length, breadth; and voyage-related details such as cargo information and navigational status (e.g. underway or at anchor).
Put simply, the Automatic Identification System (AIS) is a Very High Frequency (VHF) radio broadcasting system that transfers packets of data over the VHF data link (VDL) and enables AIS-equipped vessels and shore-based stations to send and receive identification information that can be displayed on a computer or chart plotter.
Especially when used with appropriate graphical displays, this information can help in situational awareness and provide a means to assist in collision avoidance. AIS transceivers can be found interfaced to radars and ECDIS (Electronic Chart Display and Information System) displays. When interfaced to a radar, AIS can be a source of target information, in addition to conventional ARPA (Automatic Radar Plotting Aid). AIS fitted to real (physical) aids to navigation such as floating buoys and beacons. AIS base stations can broadcast a non-physical “synthetic” AIS AtoN to appear at the location of a real (physical) AtoN on an AIS-enabled display system (e.g. AIS, ECDIS or radar). AIS base stations can also broadcast a non-physical “virtual” AIS AtoN at a particular location when no real (physical) AtoN exists.
Although AIS is not part of the GMDSS, it can be considered part of the GMDSS due to the advent of the AIS-SART (AIS Search and Rescue Transmitter), which can be used in lieu of a search and rescue radar transponder (SART), since 01 January 2010. AIS transceivers on ships also have a simple text communications capability called Short Safety- related Messaging (SSRM), but does not constitute a distress- alerting system, and uses the VHF maritime mobile band.
Each AIS station consists of one VHF transmitter, two VHF receivers (AIS 1 and AIS 2), one VHF DSC receiver (CH.70), a standard marine electronic communications link and sensor systems. Timing and positional information comes from a Global Navigation Satellite System (GNSS) receiver.
The GMDSS regulations allow vessels trading exclusively within A1 areas to carry an EPIRB operating on VHF channel 70 in lieu of a 406 MHz EPIRB.
The VHF DSC EPIRB must be capable of transmitting a Distress Alert using digital selective calling techniques. In order that it may be located by searching ships and aircraft, the EPIRB must also be capable of transmitting X-band radar locating signals.
VHF DSC EPIRBs are not fitted to GMDSS vessels, and are rarely if ever, used elsewhere.
A proposed new variant of the 406 MHz EPIRB includes an AIS burst transmitter as an additional locating aid. The designation of this device is EPIRB-AIS. The AIS burst transmitter will operate in a similar way to an AIS-SART, transmitting an updated position via AIS. The IMO has stipulated that these devices must still include a 121.5 MHz homing beacon for aircraft (or suitably equipped ships).
Although an international numbering format for the numerical identities (MMSI) to be used for the AIS transmitter has been agreed (974xxyyyy), these devices have yet to be brought into service.
It has also been agreed that the associated text to be transmitted by the AIS transmitter in active mode is EPIRB-ACTIVE, and EPIRB-TEST in test mode.
Every year valuable resources are wasted in locating EPIRBs which have been activated inadvertently. Masters and Officers need to be aware that even a single burst from a 406 MHz EPIRB can be detected instantaneously by the Cospas–Sarsat GEOSAR system which will result in an RCC being alerted. As to US Coast Guard report: 96% 406 MHz EPIRB Alerts are false.
Should it be suspected that an EPIRB has been activated inadvertently, the Master or person responsible for the vessel must immediately advise the MRCC for their area of operation.
Real-time beacon monitoring is offered to be used as a tool to detect all local inadvertent activation.
406MHz Sarsat Beacon Monitor allows to locate and process all false emergency signals on local area and gives the right to port and airport authorities to contribute penalty charges for false distress signal in accordance with Cospas-Sarsat recommendations.
Cospas-Sarsat was initially developed under a memorandum of understanding among agencies of Canada, France, the former Union of Soviet Socialist Republics and the United States of America, signed in 1979.
Through their association with the programme, States contribute ground receiving stations that enhance Cospas-Sarsat distress alerting capabilities and/or participate in international Cospas-Sarsat meetings dedicated to the worldwide coordination of system operations and programme management.
The objectives of Cospas–Sarsat are to ensure the long– term operation of the system, provide distress alert and location information on a non–discriminatory basis and support the search and rescue objectives of the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO).
The system comprises of:
A space segment operating in low–Earth orbit (LEO) and geostationary orbit (GEO);
A ground segment consisting of satellite receiving stations, known as local user terminals (LUT), and data distribution centres, known as mission control centres (MCC);
and Emergency radio beacons operating at 406 MHz, the characteristics of which comply with appropriate provisions of the International Telecommunication Union (ITU) and Cospas– Sarsat specifications. Further information on the Cospas–Sarsat system can be found in the Admiralty List of Radio Signals (ALrS) Vol. 5.