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From Mirrorbow Technologies Ltd |
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| PlaneGadget Radar USB ADS-B Receiver | MarineGadget Radar USB AIS receiver |
| About ADS-B | Buy Now | Accessories | ADS-B FAQ | About AIS | Software Options | AIS Accessories | AIS FAQ |
AIS
AIS stands for Automatic Identification System. Ships transmit information regularly about their name, MMSI Number, position, their speed, course, type and current status (at anchor for example). 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
Although you cannot rely on every ship transmitting (and should always keep a visual lookout if on on board your own vessel) most larger ships such as tankers, cargo, ferries, cruise ships etc carry AIS transponders. Some smaller craft also carry them, as an owner can have an AIS transponder fitted to increase their visibility.
AIS is trasmitted on two frequencies, Channel A (161.975Mhz) and Channel B (162.025Mhz). Ships transmit alternately on A and then B in order to maximise their chances of being seen. So assuming there is no interference listening on one of the channels will result is picking up each ship. Because the frequencies are VHF range is normally limited by line of sight, similar to that of a marine radio (10-50miles depending on your elevation). However under tropospheric ducting conditions (where the meteorological conditions are right) the range can increase considerably to over 250miles.
Using AIS on board your boat along with chart plotting software and GPS can give you an aid to navigation (may not be used for primary navigation and is no substitite for keeping a visual lookout). Your position and those of ships around you can be plotted. In addition ships are identified by their name and MMSI number which allows you to call them on your marine radio if there is concern over collision.
For more information please go to wikipedia here or google AIS Automatic Identification System