Radio Survey

Since 1 January 2010, AIS – Search and Rescue Transmitters can be carried in lieu of Search and Rescue Radar Transponders on vessels subject to the 1974 SOLAS Convention.

The AIS-SART is designed to transmit AIS messages that indicate the position, static and safety information of a unit in distress. An AIS-SART has an integral position source (e.g. a GPS receiver) and accordingly, AIS stations receiving the AIS-SART signal are able to display the range and bearing to the AIS-SART.

AIS-SARTs can only be detected by AIS installations. They cannot be interrogated, and transmit autonomously once activated. AIS-SARTs use the Self-organizing Time Division Multiple Access (SOTDMA) protocol in the similar way to a Class A mobile AIS station.

An AIS-SART is designed to be deployed in a similar way to a SART in that it is designed to operate from a survival craft at a height of 1 m above sea level. It may be fitted as an integral part of a survival craft, and can be manually activated or de-activated. Automatic activation may be provided. It is supplied with a buoyant lanyard of highly visible yellow/orange colour to secure it to the survival craft.

An AIS-SART is to be equipped with a means which is either visual or audible, or both visual and audible, to indicate correct operation locally and be provided with test facilities for all functionalities using specific test information. An indication will be provided to show that the AIS-SART has been activated, is undergoing test and has completed test. There will also be an indication of the position fixing system status when the AIS-SART is activated.

The pre-set broadcast messages of SART TEST or SART ACTIVE should be seen as text adjacent to an AIS-SART target symbol on AIS installations fitted on vessels or shore stations in VHF reception range of the unit in distress, and is to be clearly distinguished from an AIS installation (i.e. a ship, AIS AtoNs, etc). In ships fitted with an AIS MKD (Minimum Keyboard and Display), the text only will be seen, together with range and bearing.

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.