Extended Operational and Trade Vocabulary

AIS, GMDSS, IALA Buoyage and Aids to Navigation glossary

The communications and aids-to-navigation vocabulary: the GMDSS sea areas (A1 to A4) by communications coverage, EPIRB, PLB, and AIS-SART distress equipment, the IALA buoyage regions, and the buoy, beacon, and light terminology. Grounds each term in the GMDSS regulation or the IALA buoyage standard it depends on.

263 defined terms.

Showing 250 on this page (page 1 of 2).

A

A1 Sea Area: GMDSS area within VHF DSC coverage of at least one coast station, typically 20 to 30 nautical miles.
A2 Sea Area: GMDSS area within MF DSC coverage of at least one coast station, excluding A1, typically out to 100 to 200 nautical miles.
A3 Sea Area: GMDSS area within geostationary satellite (Inmarsat) coverage, excluding A1 and A2, roughly 76 N to 76 S.
A4 Sea Area: GMDSS area outside A1, A2 and A3, comprising the polar regions above 76 latitude.
ACR Electronics: US manufacturer of EPIRBs, PLBs and AIS-SARTs (e.g., GlobalFix V4/V5).
Active AtoN: Aid to navigation that emits light, sound or radio signals, requiring a power source.
Admiralty List of Lights: UK Hydrographic Office publication NP74 to NP84 listing lights, fog signals and Racons worldwide.
Admiralty List of Radio Signals (ALRS): UKHO series NP281 to NP286 covering radio communications, satellite services, radio aids, meteorology, GMDSS and pilot services.
Aft AIS Antenna Position (D): Distance from the AIS GNSS antenna reference to the stern, used with A, B, C to define vessel dimensions.
AIS: Automatic Identification System, a VHF data broadcast system mandated by SOLAS V/19.2.4.
AIS AtoN: Aid to Navigation broadcast using AIS Message 21; can be real, synthetic or virtual.
AIS Base Station: Shore-based AIS station that manages slot assignments and transmits Message 4.
AIS Class A: Mandatory transponder for SOLAS vessels broadcasting MMSI, position, course, speed.
AIS Class B: Lower-power transponder used by smaller, non-SOLAS craft.
AIS Message 1/2/3: Class A scheduled, assigned and response position reports.
AIS Message 12: Addressed safety-related message.
AIS Message 14: Safety-related broadcast message.
AIS Message 15: Interrogation request to another AIS station.
AIS Message 17: DGNSS broadcast binary message.
AIS Message 18: Class B standard position report.
AIS Message 19: Class B extended position report including static data.
AIS Message 20: Data link management message used by base stations to reserve slots.
AIS Message 21: Aid-to-Navigation report.
AIS Message 22: Channel management message for regional AIS configuration.
AIS Message 23: Group assignment command to a set of stations.
AIS Message 24: Class B static data report (Parts A and B).
AIS Message 27: Long-range position report for satellite AIS reception.
AIS Message 4: Base station report containing UTC, date and position.
AIS Message 5: Class A static and voyage-related data including IMO number, call sign, name, type, dimensions, draft, destination and ETA.
AIS Message 6: Addressed binary message between two stations.
AIS Message 7: Binary acknowledgement.
AIS Message 8: Binary broadcast message used for meteorological, hydrological and other application-specific data.
AIS Message 9: Position report for SAR aircraft.
AIS-SART: AIS Search and Rescue Transmitter for survival craft.
ALRS Volume 5: GMDSS volume of the UK Admiralty List of Radio Signals.
Alternating Light (Al): Light character showing different colors in succession.
Anchor light: All-round white light shown by a vessel at anchor.
Anchored AtoN: Floating aid (buoy) moored to the seabed with chain and sinker.
Application-Specific Message (ASM): AIS Message 6 or 8 encoded per IALA Guideline 1028.
ATIS: Automatic Transmitter Identification System used on inland VHF radios in Europe under the RAINWAT agreement.
AtoN: Aid to Navigation, any device or system external to a vessel designed to assist navigation.
Auto DSC: Automatic DSC distress alert function on VHF/MF/HF radios.

B

Base Station ID: 9-digit MMSI of an AIS shore station, format 00MIDXXXX.
Beacon: Fixed AtoN, lit or unlit.
Bifurcation Buoy: Preferred-channel mark indicating the channel divides.
Binary Broadcast Message: AIS Message 8 used to send ASMs to all stations in range.
Bow Antenna Offset (A): Distance from AIS GNSS antenna to bow.
Bridge-to-Bridge: Inter-vessel VHF communication on Channel 13 (156.650 MHz) in the US per 33 CFR 26.
Buoy: Floating navigation mark or float used to mark a mooring.
Buoyage System: Coordinated set of marks defined by IALA MBS to indicate the lateral and cardinal directions of safe water.

C

Call sign: vessel's unique radio identifier used during port communications.
CAN Buoy: Cylindrical can-shaped buoy, typically used as a port-hand lateral mark in IALA Region A.
Cardinal mark: IALA buoy indicating safe water lies to the named cardinal side.
Carriage Requirements: SOLAS V/19 list of equipment that ships must carry, including AIS, EPIRB, SART and NAVTEX.
CCIR: Former name of the ITU-R, originator of many maritime radio recommendations.
CEPT: European Conference of Postal and Telecommunications Administrations, source of inland AIS and ATIS regulations.
Channel 06: VHF inter-ship safety channel, 156.300 MHz.
Channel 09: VHF supplementary calling channel in the US, 156.450 MHz.
Channel 13: VHF bridge-to-bridge navigational channel, 156.650 MHz.
Channel 16: VHF international distress, safety and calling channel, 156.800 MHz.
Channel 67: VHF small-craft safety channel in the UK, 156.375 MHz.
Channel 70: VHF Digital Selective Calling channel, 156.525 MHz; voice prohibited.
Channel 75/76: VHF guard bands adjacent to Channel 16; 1 W maximum power.
Channel 87B: AIS 1 channel, 161.975 MHz.
Channel 88B: AIS 2 channel, 162.025 MHz.
Character of Light: Pattern of light intervals (e.g., Fl(2)10s) describing a lighted aid.
Chart datum: Lowest astronomical tide reference for hydrographic charts.
Chart No. 1: NOAA/UKHO chart symbol legend.
Cog: Single-masted Hanseatic League cargo carrier of the high medieval Baltic and North Sea.
COLREGs: Convention on the International Regulations for Preventing Collisions at Sea, 1972; the IMO rules of the road governing lights, shapes, sound signals, and collision avoidance.
Conical Buoy: Cone-shaped buoy used as starboard-hand lateral mark in IALA Region A.
Cospas-Sarsat: International satellite system for 406 MHz distress beacon detection.
CSTDMA: Carrier-Sense Time Division Multiple Access access scheme used by basic AIS Class B.

D

DGNSS: General term covering DGPS and similar augmentation.
DGPS Beacon: Marine radiobeacon transmitting differential GPS corrections in the 283.5 to 325 kHz band.
Distress alert: GMDSS message indicating grave and imminent danger.
Distress Frequency: Internationally protected frequency for distress traffic; 156.8 MHz, 2182 kHz, 121.5 MHz aviation, 406 MHz Cospas-Sarsat.
DSC: Digital Selective Calling per ITU-R M.493 and ITU-R M.541.
DSC Self-Identification: Programmed 9-digit MMSI in a DSC controller.
Dual Watch: BMP recommended doubling of bridge watch during HRA transits.

E

EGC: Enhanced Group Call service over Inmarsat (SafetyNET and FleetNET).
EPIRB: Emergency Position-Indicating Radio Beacon required under SOLAS IV/7.
EPIRB-AIS: EPIRB with integrated AIS Message 1 locator (e.g., Ocean Signal rescueME EPIRB3).
ETA: Estimated time of arrival.
EUT: Equipment Under Test, used in IEC 61108, 61162 and 62288 type approval.
EWMB: Emergency Wreck Marking Buoy with blue and yellow vertical stripes, introduced by IALA in 2006.
exactEarth: Satellite AIS data provider, now part of Spire Global.

F

F (Fixed Light): Steady, continuous light.
Fairway Buoy: Safe-water mark indicating mid-channel; red and white vertical stripes with red spherical topmark.
FCC Part 80: US regulations governing maritime radio services.
Fl (Flashing): Light character where duration of light is shorter than duration of darkness.
Fleet One: Inmarsat L-band entry service for small vessels.
Fleet Safety: Inmarsat L-band GMDSS service over Fleet Xpress hardware.
Fleet Xpress: Inmarsat Ka-band/L-band hybrid service.
FleetBroadband: Inmarsat L-band IP service in 150, 250 and 500 kbps classes (e.g., FB150, FB250, FB500).
FleetNET: Inmarsat EGC service for commercial broadcast to fleet subscribers.
Float free EPIRB: 406 MHz beacon under SOLAS.
Focal Plane: Height of a light's optical center above chart datum, used for computing geographic range.
Fog signal: Audible signal under COLREGs Rule 35 in restricted visibility.
Front Light: The lower light of a leading-lights pair, intended to be seen below the rear light when on the leading line.

G

GEOSAR: Geostationary segment of Cospas-Sarsat providing near-real-time alerting without Doppler position.
GLONASS: Russian GNSS constellation.
GMDSS: Global Maritime Distress and Safety System under SOLAS Chapter IV.
GMDSS Master Plan: IMO circular GMDSS.1 listing recognized stations and services worldwide.
GMDSS Radio Log: Statutory log of radio watch, tests and distress traffic.
GMDSS Radio Operator: Holder of a GOC or ROC issued under STCW IV/2.
GNSS: Global navigation satellite system; GPS, GLONASS, Galileo, BeiDou.
GPS: Global Positioning System, US satellite navigation system.
Group-Flashing Light: Flashing character with a group of flashes followed by an eclipse (e.g., Fl(3)15s).
GX (Global Xpress): Inmarsat Ka-band broadband network using I-5 and I-6 satellites.

H

Heading: Direction in which a vessel's bow is pointing.
HF DSC: HF Digital Selective Calling on 4207.5, 6312, 8414.5, 12577 and 16804.5 kHz.
HF NBDP: HF Narrow-Band Direct Printing (radiotelex), removed from GMDSS carriage requirement in 2024.
HF Radio: 3 to 30 MHz maritime mobile bands listed in ITU Appendix 17.
High-Focal-Plane Buoy: Tall pillar buoy with elevated lantern, used in deep water.
Hydrostatic Release Unit (HRU): Pressure-activated device that releases an EPIRB or liferaft at 1.5 to 4 m depth.

I

IALA: International Association of Marine Aids to Navigation and Lighthouse Authorities.
IALA G1028: Guideline on application-specific messages.
IALA MBS: IALA Maritime Buoyage System combining Regions A and B with cardinal, isolated danger, safe-water and special marks.
IALA Region A: Lateral marks: red to port, green to starboard when entering from seaward; used in Europe, Africa, Australia, India and most of Asia.
IALA Region B: Lateral marks: green to port, red to starboard; used in the Americas, Japan, Korea and the Philippines.
IBS: Lloyd's Register Integrated Bridge System notation.
IEC 61108-1: Type-approval standard for shipborne GPS receivers.
IEC 61162: Digital interface standard for marine electronics (NMEA 0183 family).
IEC 61162-450: Ethernet-based marine network standard.
IEC 61993-2: Type-approval standard for AIS Class A.
IEC 62287-1/-2: Type-approval standard for AIS Class B CS and Class B SO.
IEC 62288: Presentation of navigational information on shipborne displays.
IEC 62320-2: AIS AtoN type-approval standard.
IHO: International Hydrographic Organization, intergovernmental body for hydrography.
IHO S-100: Universal Hydrographic Data Model.
IHO S-101: Next-generation ENC specification.
IHO S-201: AtoN information product specification under S-100.
IHO S-4: Regulations for International (INT) Charts and Chart Specifications of the IHO.
IHO S-52: Specifications for chart content and display aspects of ECDIS.
IHO S-57: ENC product specification, edition 3.1.
IMO Number: Unique seven-digit ship identifier from IHS Markit on behalf of IMO.
Inmarsat: Satellite communications provider for GMDSS and commercial services.
Inmarsat C: Polling/EGC/SafetyNET service in GMDSS.
Inmarsat I-3, I-4, I-5, I-6: Successive generations of Inmarsat geostationary satellites in L-band and Ka-band.
INT 1: International chart symbol catalog; UK edition is NP5011; German edition is INT 1; US edition is Chart No.1.
Interrogation: AIS Message 15 used by a station to request reports from another.
Iridium Certus: L-band satellite broadband service (GMDSS-recognized 2020).
Iridium GMDSS: GMDSS satellite service approved by IMO Resolution MSC.451(99), operational from 13 December 2020.
Iso (Isophase): Light character with equal periods of light and darkness.
Isolated Danger Mark: IALA mark with black body and one or more red bands and a topmark of two black spheres, placed over isolated hazards.
ITU-R M.1084: Interim solutions for improved efficiency in the VHF maritime mobile band.
ITU-R M.1371: Technical characteristics of an automatic identification system using TDMA in the VHF maritime mobile band; current edition M.1371-5.
ITU-R M.493: DSC technical characteristics.
ITU-R M.540: NAVTEX broadcast service.
ITU-R M.541: Operational procedures for DSC.
ITU-R M.585: Assignment and use of maritime mobile service identities (MMSI).
ITU-R M.625: NAVTEX direct-printing technical characteristics.

J

Jotron: Norwegian manufacturer of EPIRBs (Tron 60), AIS-SARTs and VHF/MF/HF radios.
JRC: Japan Radio Co., manufacturer of MF/HF, Inmarsat C and AIS equipment.

K

Ka-band: 26.5 to 40 GHz satellite band used by Inmarsat Global Xpress.
Ku-band: 12 to 18 GHz satellite band used by many VSAT services.

L

Lantern: Optical assembly housing the light source of an aid.
Lateral Mark: Channel-edge buoy or beacon under the IALA system.
Leading lights: aligned shore lights marking a channel centerline.
Leading line: Line passing through two leading marks indicating a safe approach.
LEOSAR: Low Earth Orbit segment of Cospas-Sarsat providing Doppler localization.
LFl (Long Flash): Light character with a single flash of at least 2 seconds duration.
Light Float: Large, ship-shaped lighted buoy moored as a substitute for a light vessel.
Light sector: Arc through which a sectored light shows a particular color.
Light Vessel (Lightship): Manned or unmanned floating structure carrying a major navigational light, largely replaced by large automatic buoys.
List of Lights: National publications enumerating lighted aids; NGA Pub. 110 to 116 in the US.
LRIT: Long-Range Identification and Tracking, required by SOLAS V/19-1 since 31 December 2008.

M

Major Light: Light of high intensity and reliability, usually a primary seacoast or landfall light.
Manual DSC Distress: DSC distress alert initiated by pressing the red distress button for 5 seconds.
MarineTraffic: Commercial AIS data and tracking platform headquartered in Athens.
McMurdo: UK manufacturer of EPIRBs and AIS-SARTs (e.g., Smartfind G8, Smartfind S20).
MEOSAR: Medium Earth Orbit segment of Cospas-Sarsat on GPS, Galileo and GLONASS, enabling rapid global localization.
MES: Mobile Earth Station; in Inmarsat terminology, a shipborne satellite terminal.
MF DSC: Medium Frequency Digital Selective Calling on 2187.5 kHz.
MID: Maritime Identification Digits, the first three digits of an MMSI indicating country of registration.
MMSI: Maritime Mobile Service Identity, 9-digit per ITU-R M.585.
Mo (Morse Code Light): Light character flashing a Morse letter (e.g., Mo(A)).
Mooring buoy: Buoy to which a ship may secure.

N

National NAVTEX: NAVTEX service in national languages on 490 kHz.
Nautical mile: 1852 m international nautical mile.
NAVAREA: One of 21 navigational warning areas under the Worldwide Navigational Warning Service relevant to incident broadcasts.
NAVAREA Coordinator: National authority responsible for issuing NAVAREA warnings in its area.
Navigation Status: AIS field with values 0 (Under way using engine) through 15 (Not defined).
NAVTEX: GMDSS broadcast service under SOLAS IV.
NBDP: Narrow-Band Direct Printing (radiotelex), ITU-R M.476/M.625.
NCC (NAVTEX Coordinating Centre): National body coordinating NAVTEX broadcasts within a NAVAREA.
NMEA 0183: Marine electronics serial data standard.
NMEA 2000: CAN-based marine data network.
Nominal Range: Luminous range of a light in a meteorological visibility of 10 nautical miles.
Notice to mariners: NM, updates to nautical charts and publications.

O

Occulting Light (Oc): Light character in which total duration of light in a period is longer than the total duration of darkness.
Ocean Signal: UK manufacturer of compact EPIRBs (rescueME EPIRB1 and EPIRB3) and AIS-SARTs (rescueME MOB1).
Off-Position Indicator: AIS AtoN flag in Message 21 indicating the buoy has drifted from its assigned position.
Off-Station Alarm: Watch function on AtoN telemetry detecting movement beyond a watch circle.

P

Pillar Buoy: Tall buoy with a relatively wide base, usable in deep water; common for cardinal and isolated-danger marks.
PLB: Personal Locator Beacon transmitting on 406 MHz Cospas-Sarsat; not GMDSS equipment.
Polled DSC: DSC position request acknowledged automatically by a responding radio.
Port-Hand Mark: Lateral mark to be left to port when proceeding in the conventional direction of buoyage; red can in Region A, green can in Region B.
Preferred-Channel Mark: Modified lateral mark with horizontal bands of red and green indicating which side is the preferred channel.

Q

Q (Quick Flashing): Light character at 50 to 79 flashes per minute, typically used on cardinal marks.
Q(3): Cardinal East character: three quick flashes every 5 or 10 seconds.
Q(6)+LFl: Cardinal South character: six quick flashes followed by a long flash, repeated every 10 or 15 seconds.
Q(9): Cardinal West character: nine quick flashes every 10 or 15 seconds.

R

R-Mode: Ranging-mode service investigated by IALA using MF radio beacons, AIS and eLoran as a GNSS backup.
Racon: Radar transponder marking AtoNs.
Radar Reflector: Passive device enhancing radar return.
Radar SART: Search and Rescue Transponder operating in the 9.2 to 9.5 GHz X-band, producing 12 inward-moving blips on radar.
Radar Target Enhancer (RTE): Active device that amplifies and retransmits radar signals to increase effective radar cross section.
Range (Geographic): Maximum distance at which a light can be seen given Earth's curvature, observer and light heights.
Range (Luminous): Maximum distance a light can be seen given its intensity and meteorological visibility.
Range light: Two fixed lights in line indicating channel.
Rate of Turn (ROT): AIS field encoded in degrees per minute (signed), with special values for not available and turning hard.
RCC (Rescue Coordination Centre): Centre responsible for coordinating SAR operations in a search and rescue region.
Rear Light: Higher light of a leading-lights pair, intended to appear above the front light when on the leading line.
Reverse Polarity: Period when Earth's magnetic field was opposite to today, recorded in oceanic crust.

S

S-AIS: Satellite-received AIS, used to extend AIS coverage offshore (e.g., Spire, ORBCOMM, Kpler/exactEarth).
Safe-Water Mark: IALA mark with red and white vertical stripes and red spherical topmark, indicating navigable water all around.
SafetyNET: Inmarsat-C broadcast service for MSI to selected sea or NAVAREAs.
SAR Transponder (SART): Generic term covering radar-SART and AIS-SART.
SART Test: Periodic functional test performed away from the bridge and not during distress traffic.
Sector Light: Light showing different colors or characters over defined arcs to mark channels or hazards.
Self-Organizing TDMA (SOTDMA): Access scheme used by AIS Class A; each station autonomously reserves time slots.
Service Range: Aid's reliable operational range, often the lesser of luminous and geographic ranges.
Ship Earth Station (SES): Older Inmarsat term equivalent to MES.
Slot Reservation: SOTDMA mechanism for advertising future transmission slots.
SOG: Speed Over Ground transmitted in AIS in tenths of a knot; 1023 indicates not available.
SOLAS Chapter IV: Radiocommunications, including GMDSS requirements.
SOLAS Chapter V: Safety of Navigation.
Sound signal: Whistle, gong, or bell signal per COLREGs Annex III.
Spar Buoy: Long, vertical buoy of relatively small diameter, used in sheltered waters.
Special mark: IALA yellow mark indicating a special area or feature.
Spire Global: US-based satellite operator providing S-AIS services after the acquisition of exactEarth.
Spoofing: Deliberate transmission of false AIS data, often using fabricated MMSIs.
Squelch: Receiver circuit suppressing audio in the absence of signal.
Static Data: AIS fields that do not change frequently (IMO, name, call sign, type, dimensions); reported in Messages 5 and 24.
Synthetic AIS AtoN: Aid whose AIS signal is transmitted from a remote station representing a real physical aid.

T

T-AIS: Terrestrial AIS received by shore-based receivers within VHF range.
TDMA: Time Division Multiple Access, the basic medium-access scheme of AIS.
Telex Over Radio (TOR): NBDP service, formerly part of GMDSS.
Topmark: Shape mounted atop a buoy or beacon for identification.
Two-Tone Emergency Signal: 2200/1300 Hz alarm formerly used to actuate radio watch receivers; superseded by DSC.

U

UAIS: Universal AIS, the formal ITU term distinguishing the standardized system from earlier proprietary systems.
UKHO: United Kingdom Hydrographic Office, publisher of Admiralty charts.
UTC: Coordinated Universal Time; AIS timestamps are referenced to UTC seconds.

V

VDES: VHF Data Exchange System, ITU-R M.2092, an evolution of AIS adding ASM and VHF Data Exchange channels with satellite component.
VDL: VHF Data Link; the shared radio medium used by AIS and VDES.
VDM/VDO: NMEA 0183 sentences for AIS received and own-vessel data.
VDR: Voyage Data Recorder, required under SOLAS V/20.
VesselFinder: Commercial AIS tracking provider based in Varna, Bulgaria.