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What is AIS?
a tecnical info from weatherdoc inc.
AIS stands for Automatic Identification System (AIS)
Summary:
The Automatic Identification System (AIS) is a maritime transponder/reciever system defined by the IMO.(international maritime organisation)
AIS operates in the VHF frequency band.
AIS main objectives are :
- to improve maritime safety
- to protect the maritime environment
Practically the AIS:
- assists collision avoidance (AIS ship-to-ship)
- enables ports and coastal states to identify ships and to managesand supervise the traffic in their waters (AIS Coast station).
Description :
AIS is a system used by ships and vessels for identification at sea. AIS helps to resolve the difficulty of identifying ships when not in sight (e.g. at night, in radar blind arcs or shadows or at distance) by providing ID, position, course, speed and other ship data with all other nearby ships and VTS stations. The IMO SOLAS requires AIS to be fitted aboard all ships of gross tonnage >= 300 for international voyages. The ship datas are displayed on a AIS data capable chartplotter with an ship symbol or even on AIS data capable navigation software.
AIS transponders automatically transmit the position and velocity of the ship at regular intervals via a VHF radio built into the AIS. The position and velocity originate from the ship's GPS or, if that fails, from an integral GPS receiver. The AIS also receives heading information from the ship's compass and transmits this at the same time. Other information, such as the vessel name and VHF call sign, is entered when installing the equipment and is transmitted less frequently. The signals are received by AIS transponders fitted on other ships or on land based systems, such as VTS systems.
In order to ensure that the VHF transmisions of different AIS transponders do not occur at the same time they are time multiplexed. In order to make the most efficient use of the bandwidth available, vessels which are anchored or are moving slowly transmit less frequently than those that are moving faster or are manoeuvering. The update rate of fast manoeuvering vessels is similar to that of a conventional marine radar.
AIS transponders automatically transmit the position and velocity of the ship at regular intervals via a VHF radio built into the AIS. The position and velocity originate from the ship's GPS or, if that fails, from an integral GPS receiver. The AIS also receives heading information from the ship's compass and transmits this at the same time. Other information, such as the vessel name and VHF call sign, is entered when installing the equipment and is transmitted less frequently. The signals are received by AIS transponders fitted on other ships or on land based systems, such as VTS systems. In order to ensure that the VHF transmisions of different AIS transponders do not occur at the same time they are time multiplexed. In order to make the most efficient use of the bandwidth available, vessels which are anchored or are moving slowly transmit less frequently than those that are moving faster or are manoeuvering. The update rate of fast manoeuvering vessels is similar to that of a conventional marine radar.
AIS transceiver sends the following data every 2 to 10 seconds depending on vessels speed while underway, and every 3 minutes while vessel is at anchor. This data includes :
- MMSI number of vessel - vessel's unique identification
- Navigation status - "at anchor", "under way using engine" or "not under command"
- Rate of turn - right or left, 0 to 720 degrees per minute
- Speed over ground - 0.1 knot resolution from 0 to 102 knots
- Position accuracy
- Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
- Course over ground - relative to true north to 0.1 degree
- True Heading - 0 to 359 degrees from eg. gyro compass
- Time stamp - UTC time accurate to nearest second when this data was generated
Not all of above datas are displyed (Quantity of shown datas is software of the Chartplotter).
Typically you can see on the chartplotter following datas :
- MMSI number of vessel - vessel's unique identification
- Speed over ground - 0.1 knot resolution from 0 to 102 knots
- Course over ground - relative to true north to 0.1 degree
In addition, the following data is broadcast every 6 minutes:
- MMSI number - vessel's unique identification
- IMO number
- Radio call sign - international radio call sign assigned to vessel
- Name - Name of vessel, max 20 characters
- Type of ship/cargo
- Dimensions of ship - to nearest meter
- Location of positioning system's (eg. GPS) antenna onboard the vessel
- Draught of ship - 0.1 meter to 25.5 meters
- Destination - max 20 characters
- ETA (estimated time of arrival) at destination - UTC month/date hour:minute
The AIS is mandatory since 2002 for ships constructed on or after July 2002. It is already fully effective for passenger ships and tankers constructed before July 2002 engaged on international voyages. End of July 2004, it will be mandatory to all cargo ships 50,000 gt engaged on international voyages. It will be adopted by all ships of 300 gt and upwards engaged on international voyages or not, in 2008.
Above given information is not complete and should give only an overview about the AIS topic. For more details please have a look to the following links :
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