History of AIS
It’s not entirely clear who it was that came up with the first AIS vessel tracking and identification system, but like so much other technology that we take for granted these days, it came out of the introduction of GPS for civilian purposes, which achieved global coverage in the early 1990s. It was then the integration of GPS time and position data with long-standing VHF radio technology that enabled the development of AIS. We’ll delve into a bit more into the history of AIS in this article.
The early years
In its early years its primary use was as a ship-to-ship anti-collision system for use in poor visibility and at night, in support of radar and conventional watch keeping. Over time the amount of information that could be transmitted in the VHF signal grew and its usefulness increased. In 2002 it finally went global when the IMO in its landmark SOLAS convention mandated that all passenger ships and other commercial vessels over 300 GT should carry Class-A AIS transceivers. At the time this affected around 100,000 ships, but since then use has expanded as the unit cost of transceivers has fallen and both compulsory and voluntary adoption has increased.
The final frontier
Originally developed as a short range identification and vessel tracking system, at the start of the 21st century it was discovered that AIS transmissions could be received at ranges of up to 400km above the surface of the earth, whereas on the surface the maximum effective distance is around one tenth of that. This revolutionised AIS, taking it from a coastal and ship-to-ship tracking application to a vessel management system with global coverage. However, the challenge for satellite operators looking to develop this opportunity now is managing the enormous volumes of data that this creates for individual satellites each monitoring thousands of square kilometres of ocean.
The AIS format uses TDMA radio access that allows for just 4,500 time slots per minute. One time slot equates to a single vessel transmission. Any more than that and the individual signals start to interfere with each other, corrupting the data held within. The terrestrial AIS infrastructure with its short range and higher density does not have the same capacity problems.
The satellite developers are, however, working on ways of receiving and processing incoming data at faster rates and rapid advances are being made.
An important tool in the box
There is no perfect vessel tracking system, but AIS is becoming increasingly effective as accuracy and refresh rates get ever better. Its ability to interface with other detection sources makes it an important component of integrated navigation and warning systems, and the addition of supplementary environmental and situational data makes it yet more versatile. Without a doubt AIS is now one of the most valuable information sources available for anyone involved in the maritime sector.
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.
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