The International Maritime Organization’s (IMO) International Convention for the Safety of Life at Sea (SOLAS) requires AIS to be fitted aboard international voyaging ships with gross tonnage (GT) of 300 or more tons, and all passenger ships regardless of size. It is estimated that more than 40,000 ships currently carry AIS class A equipment.
Ships outside AIS radio range can be tracked with the Long Range Identification and Tracking (LRIT) system with less frequent transmission.
AIS Range limitations and space-based tracking
Shipboard AIS transponders have a horizontal range that is highly variable but typically only about 74 kilometers (46 mi). They reach much further vertically, up to the 400 km orbit of the International Space Station (ISS).
In November 2009, the STS-129 space shuttle mission attached two antennas – an AIS VHF antenna, and an Amateur Radio antenna to the Columbus module of the ISS. Both antennas were built in cooperation between ESA and the ARISS team (Amateur Radio on ISS). Starting from May 2010 the European Space Agency is testing two different AIS receivers, one from Luxspace (GdL), one from FFI (Norway) in the frame of technology demonstration for space-based ship monitoring. This is a first step towards a satellite-based AIS-monitoring service.[4]
In 2008, ORBCOMM launched new low-earth orbit (LEO) satellites, equipped with the capability to collect AIS data. Additionally, ORBCOMM has incorporated the ability to receive, collect and forward AIS data in the design of the next 18 ORBCOMM Generation 2 (0G2) satellites under development. As additional satellites are launched, ORBCOMM will increase its capability by providing greater redundancy and more frequent updates of AIS data.[5] In 2009, LUXSPACE, a Grand Duchy of Luxembourg based company has launched PathFinder2, (ex-Rubin) and is now the only European company to have an operational system in orbit providing data from all over the world on a daily basis. The satellite is operated in cooperation with SES ASTRA and REDU Space Services. [6] In 2007, a previous test of space-based AIS tracking by the U.S. TacSat-2 satellite suffered from signal corruption because the many AIS signals interfered with each other.
http://en.wikipedia.org/wiki/Automatic_Identification_System
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