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IAMSAR Manual
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Communications
2.4 Modes of Emission
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2.4.1 Two radios which operate on a common frequency can usually communicate with each other within range; however, they must also use the same mode of emission. Emission modes are discussed in the ITU Radio Regulations. Different emission modes could prevent an aircraft and ship from communicating directly with each other even if they share a common frequency.
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2.5 Global Maritime Distress and Safety System |
2.5.1 After 1 February 1999, ships subject to the Safety of Life at Sea (SOLAS) Convention are obliged to be outfitted with certain communications equipment, collectively referred to as the shipboard portion of the Global Maritime Distress and Safety System (GMDSS). Certain fishing vessels and other marine craft may also carry GMDSS-compatible equipment.
2.5.2 Information on communications Equipment which each SOLAS vessel carries should be available to RCCs via ITU publications and databases, if the vessel's flag State promptly informs ITU as required. Otherwise, RCCs may need to seek this data from the flag States, communications service providers, ship reporting system databases, or other sources. The information sources are called SAR data providers (SDPs); all GMDSS equipment should be registered with ITU or other suitable SDP which makes the data readily available to RCCs world-wide to support SAR.
2.5.3 RCC personnel should be familiar with the SOLAS GMDSS provisions, and associated IMO documents. GMDSS takes advantage of available technology to shift alerting emphasis from ship-to-ship (though this can still be done), and towards ship-to-shore, where SAR professionals can help arrange assistance. GMDSS capabilities of vessels not subject to SOLAS range from full compliance with SOLAS to no capabilities at all.
2.5.4 GMDSS-equipped ships can be expected to perform the following functions wherever they operate:
- transmit ship-to-shore distress alerts by two independent means;
- receive shore-to-ship alerts (usually relayed by RCCs); and
- transmit and receive:
- ship-to-ship alerts;
- SAR co-ordinating communications;
- on-scene communications;
- locating signals;
- maritime safety information;
- general radio communications to and from shore; and
- bridge-to-bridge communications.
2.5.5 After 1 February 1999, most SOLAS ships can be expected to have at least the following equipment (consult the SOLAS Convention and paragraphs 2.5.6 through 2.5.13 for requirements):
- VHF radiotelephone (Channels 6, 13, and 16);
- VHF DSC (Channel 70) transmitter and watch receiver;
- SART;
- NAVTEX receiver;
- EGC if operating outside NAVTEX range; and
- VHF DSC or satellite EPIRB, as appropriate.
2.5.6 Channel 6 may be used for communications with vessels for SAR operations. Channel 13 is used for safety of navigation ship-to-ship. Channel 16 is used for distress and safety traffic, and also may be used by aircraft for safety purposes. Channel 70 is used as a digital selective calling (DSC) channel in the maritime mobile service for distress, safety, calling, and reply.
2.5.7 DSC is used for calling and replying, and for transmitting, acknowledging and relaying distress alerts. It allows a specific station to be contacted and made aware that the calling station wishes to communicate with it, and to indicate how to reply, or what station to listen to for subsequent distress traffic. It also can make "all ships" calls. Follow-up communications are made on an appropriate non-DSC frequency. DSC radio users need to understand the basic operation of the radio, how DSC acts as an automated watch, and the importance of registering the radio and keeping it on and tuned to the DSC channel.
2.5.8 SOLAS ships sailing beyond range of a VHF DSC coast radio station must also have an MF DSC (2187.5 kHz) transmitter and watch receiver. If sailing beyond range of an MF DSC coast radio station, they must have an Inmarsat Ship Earth Station (SES) or an MF/HF DSC transmitter and watch receiver including narrow-band direct printing (NBDP). If operating outside Inmarsat coverage (i.e., in the polar areas), they must have the MF/HF DSC capability.
2.5.9 Narrow-band direct printing (NBDP) is a radio telex system.
2.5.10 A search and rescue radar transponder (SART) interacts with vessel or aircraft radars (9 GHz) for locating survival craft. SART responses show up as a distinctive line of 12 equally spaced blips on compatible radar displays, providing a bearing and range to the SART. A SART is a portable device which should be taken into a lifeboat or liferaft when abandoning ship.
2.5.11 NAVTEX is an NBDP telex system for promulgating safety information which is automatically printed by an on-board NAVTEX receiver. NAVTEX range is generally less than 300 nautical miles from the broadcasting station. NAVTEX receivers are designed to ignore repeated broadcasts they have already received, and to sound an alarm upon receipt of urgent or distress traffic. Users can programme the equipment to receive only the types of information they want to be automatically printed out. All properly formatted NAVTEX messages contain a content indicator in their heading. The printing of certain categories of messages cannot be suppressed regardless of the number of times it is received. NAVTEX receivers are relatively inexpensive; boaters and other seafarers should be encouraged to use them and to leave them turned on when under way.
2.5.12 Enhanced group call (EGC) is part of the Inmarsat system that complements the NAVTEX system to supply SafetyNET and similar services (Inmarsat and SafetyNET are further discussed later in this chapter). SafetyNET is used by SAR, meteorological, and navigation authorities for promulgation of maritime safety information (MSI). Some Inmarsat coast earth stations (CESs) also offer EGC FleetNET services used for fleet management and general information to particular groups of ships; RCCs may find such services useful for certain applications, such as sending messages to a standard list of other RCCs.
2.5.13 GMDSS introduces better communications for certain vessels, but leaves the existing terrestrial system for others; some effects are that SAR authorities must support two maritime mobile systems, and some vessels cannot call each other. For example, when SOLAS ships discontinue watchkeeping on Channel 16 in favour of automated technologies, most vessels will still depend on Channel 16 for distress, safety, and calling. |
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2.6.1 Two types of maritime satellite emergency position-indicating radio beacons (EPIRBs) have been accepted into GMDSS:
- 406 MHz satellite EPIRBs whose signals are relayed via Cospas-Sarsat satellites, local user terminals (LUTs) and Mission Control Centres (MCCs) to SAR Points of Contact (SPOCs) (SPOCs include RCCs where established); and
- Inmarsat-E EPIRBs, whose distress messages are relayed via Inmarsat satellites and Inmarsat-E CESs to Inmarsat-E RCCs.
2.6.2 LUTs are Cospas-Sarsat earth stations. MCCs collect, store, and sort data from LUTs and other MCCs, exchange data within the system, and provide alert messages to the SPOCs, which include points outside the SAR system where no RCC is available.
2.6.3 Cospas-Sarsat also relays alerts from aviation 406 MHz satellite emergency locator transmitters (ELTs), and from 406 MHz satellite Personal Locator Beacons (PLBs). Signals are also relayed via overflying aircraft and satellite from 121.5 and 243 MHz EL Ts and EPIRBs, not specifically designed for satellite compatibility nor considered part of GMDSS. All 406 MHz satellite beacons are electronically similar, the main differences being packaging, activating mechanisms, and slight differences in coding protocols. While ELTs, EPIRBs, and PLBs each have intended user communities, unintended users may activate the devices in an emergency.
2.6.4 Close to shore, non-satellite VHF EPIRBs using Channel 70 may be used in lieu of satellite EPIRBs where receiving stations are available.
2.6.5 Most ELTs, EPIRBs, and PLBs provide homing signals on 121.5 MHz; some also use 243 MHz, and some EPIRBs may also integrate SARTs into their designs.
2.6.6 Most EPIRBs and ELTs are designed to activate automatically when a vessel sinks or an aircraft crashes (EPIRB alerts tell whether the beacon was activated automatically or manually). PLBs are manually activated. Some PLB users may carry the devices for use aboard aircraft or vessels, 1hough they are not designed to be equivalent to, nor suitable for use as, EPIRBs or ELTs. (For ITU purposes, the term "EPIRB" is generically applied to radio beacons like EPIRBs, ELTs, and PLBs.)
2.6.7 RCCs use the message country codes to direct them to the appropriate States where information can be obtained about the distressed craft from emergency databases (if owners of coded 406 MHz ELTs and EPIRBs properly registered the beacons); 121.5 and 243 MHz beacons are not coded and registered. (The country codes directly correspond to the ITU maritime identity digits (MIDs) used to identify flag States.)
2.6.8 A Cospas-Sarsat satellite must be in view of both a beacon and a LUT at the same time for 121.5/243 MHz signals to be relayed; this requires many LUTs for broad geographic coverage, and is called the local mode of operation.
2.6.9 Signals from 406 MHz ELTs and EPIRBs can be stored aboard a satellite and relayed to ground later if no LUT receiver is immediately within view of the satellite, enabling the system to operate in a global mode with fewer LUTs required;
Note: For more information on equipment, performance standards, alert messages, distribution procedures, users instructions, and other Cospas-5arsat related matters, Cospas-Sarsat Secretariat should be contacted.
2.6.10 Inmarsat-E EPIRBs transmit messages via Inmarsat geostationary satellites and CESs, to RCCs. These beacons have registered coded EPIRB identities in an Inmarsat-E database associated with all registration data. Position information from Inmarsat-E EPIRBs is derived either from integral equipment such as GPS or via interfaces with shipboard navigation equipment (positions from shipboard equipment cannot be updated after the EPIRB floats free). Inmarsat-E EPIRBs operate within Inmarsat's coverage area.
Note: For more information on equipment, performance standards, alert messages, distribution procedures, user instructions, and other Inmarsat-E-related matters, Inmarsat should be contacted.
2.6.11 Users of ELTs and EPIRBs need to be informed about how to properly install, register, and use this equipment, and what happens when these devices are activated. They should be made to understand that these are the alerting means of last resort, which should not be depended upon to replace two-way communications as the primary means of alerting. |
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2.7 Satellite Communications |
2.7.1 Other satellite systems are available which can be used for distress alerting with various degrees of effectiveness, but the primary ones used for SOLAS compliance are Cospas-Sarsat and Inmarsat.
2.7.2 Inmarsat uses satellites in each of the areas listed below. Together the satellites provide coverage along the entire equator between 70� latitude north and south, and serve aeronautical, land, and maritime users.
- Atlantic Ocean Region-East (AOR-E)
- Pacific Ocean Region (POR)
- Indian Ocean Region (IOR)
- Atlantic Ocean Region -West (AOR-W)
2.7.3 Ocean area access codes for contacting vessels via satellite vary. RCCs must be aware of the telephone and telex access codes (similar in use to international telephone access numbers) appropriate for their service providers.
2.7.4 Inmarsat type-approved ship earth stations (SESs) and aeronautical earth stations (AESs) transmit via the satellites to land earth stations (LESs), also known as coast earth stations (CESs) for maritime functions and ground earth stations (CESs) for aeronautical functions. Each ocean area has at least one Network Co-ordinating Station (NCS) which manages multiple system uses and users.
2.7.5 A variety of Inmarsat equipment may be used by vessels to send distress alerts, each with its own capabilities. Some have a distress button which can send basic pre-formatted automatic data alerts. Most Inmarsat alerts provide position data which has been automatically updated, but some equipment alternatively offers manual updating, which experience has shown to be unreliable.
2.7.6 Inmarsat-A and -B SESs can handle distress communications, telephone calls, telex calls, facsimile, data:, and other general services. The Inmarsat-C SES is a message-only transfer terminal; it does not handle voice communications, but it is important because of its ECC capability, relatively low cost to obtain and operate, versatility when coupled with a personal computer, and widespread use. Various types of Inmarsat-C terminals are also used on land by trucks and other mobile units. Other common maritime terminals carry Inmarsat designations such as M and E (E is the EPIRB). |
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