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A guide to AIS acronyms

AIS acronyms

The global AIS vessel tracking and vessel identification system comes with its own set of technical terms and acronyms. Many people are probably asking “what is AIS” and “what’s live ship tracking”. To the non-professional user these can require time-consuming interpretation and online searches. Below is a cut-out-and-keep guide to those that we encounter on a regular basis.

AIS                     Automated Identification System

AIS – SART     AIS Search And Rescue Transponders are self-contained radio devices that when activated transmit distress signals together with position information and an MMSI  identification code on standard SAR frequencies.

API                    Application programming Interface is a set of routines, protocols, and tools for building software applications. An API specifies how software components should interact and APIs are used when programming graphical user interface (GUI) components.

Class-A             Class-A transceivers are high-specification AIS units mandated by the IMO for all passenger and commercial vessels over 300 GT.

Class-B             Class-B transceivers are low-power, lower-specification AIS units for light commercial and leisure vessels.

GMDSS            Global Maritime Distress Safety Signal – an international system that uses a range of technologies to ensure the rapid alerting of the authorities to any maritime emergency.

GMSK               Gaussian minimum shift keying is the continuous-phase frequency-shift keying modulation scheme used in digital communication. It is used by AIS to reduce out-of-band interference.

GNSS                Global Navigation Satellite System(s) typically are the onboard source of the GPS position data that is fed into the AIS.

GPS                   Global Positioning System – the ultimate, space-based, source of the position data that underpins AIS.

IMO-SOLAS     International Maritime Organisation – Safety of Life At Sea: the international organisation that is responsible for the global legal framework that governs operations at sea, and its principle directive that sets safety standards and requirements for all vessels.

ISPS                   The International Ship and Port Facility Security code is an amendment to the SOLAS convention that specifies minimum security arrangements for ships and ports.

MMSI                Maritime Mobile Service Identity is the unique, nine-digit number used to identify individual vessels, SAR aircraft and shore stations via AIS and other radio-based systems.

S-AIS                 Satellite AIS describes the AIS transmissions and software applications that use space-based systems instead of terrestrial systems.

SARSAT            Search And Rescue Satellite Aided Tracking

SDP                     Spectrum De-collision Processing is the process where multiple AIS signals received simultaneously by a single receiver are digitised  and then filtered using software to increase the clarity of individual signals.

SDPOB              Spectrum De-collision Onboard is where the SDP process takes place on a satellite rather than at a ground station.

SSAS                 Ship Security Alert System is part of the ISPS code and is a system that contributes to the IMO’s efforts to strengthen maritime security. The system is a IMO regulated system. In case of attempted piracy etc, the ship’s SSAS beacon can be activated, and appropriate law-enforcement forces despatched.

T-AIS                Terrestrial AIS describes the AIS transmissions and software applications that use short-range, land-based systems.

VTS                   Vessel Traffic Service(s) are system used by harbour and other authorities to monitor vessel traffic. Among its other applications, BigOceanData is a high-specification VTS.


About BigOceanData
BigOceanData is a leader in maritime tracking and telemetry, delivering global vessel tracking and monitoring services along with fleet management tools via its sophisticated browser-based interface. Key features of the BigOceanData product include its ability to fuse data from AIS signals and a range of onboard satellite reporting systems so as to both improve position accuracy and reduce data costs. The system also integrates a series of data feeds and management tools that show users not only vessel locations and movements, but situational data such as marine charting, terrestrial mapping, weather and sea-state (current and forecast), and piracy and other security alerts.

For more information contact or call +44 (0) 207 998 3048.

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BigOceanData is a vessel tracking software portal and service provider for maritime and vessel management.

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