AUTOMATIC IDENTIFICATION SYSTEM
The Automatic Identification System (AIS) is an automated tracking system used on ships and by Vessel Traffic Services (VTS) for identifying and locating vessels by electronically exchanging data with other nearby ships and VTS stations. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport. The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, which is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. It uses Self-Organizing Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure reliable ship-to-ship operation
Picture a shipboard radar or an electronic chart display that includes a symbol for every significant ship within radio range, each as desired with a velocity vector (indicating speed and heading). Each ship "symbol" can reflect the actual size of the ship, with position to GPS or differential GPS accuracy.
By "clicking" on a ship symbol, you can learn the ship
· name,
· course and speed,
· classification,
· registration number,
· MMSI number (Maritime Mobile Service Identification)
and other informations like:
· Maneuvering information,
· closest point of approach (CPA),
· time to closest point of approach (TCPA)
This display information was previously available only to modern Vessel Traffic Service operations centers… it is now available to every AIS user.
Saab R4 ClassA AIS ship borne transponder system
A graphical display of AIS data on board a ship.
An AIS-equipped system on board a ship presents the bearing and distance of nearby vessels in a radar-like display format.
A vessel's text-only AIS display, listing nearby vessels' range, bearings, and names
With this display information, you can
· call any ship over VHF radiotelephone by name
· dial it up directly using any GMDSS equipment. · send and receive short safety-related email messages to and from the ship.
HOW AIS WORKS
Each AIS system consists of
one VHF transmitter,
two VHF TDMA receivers,
one VHF DSC receiver,
and standard marine electronic communications links (IEC 61162/NMEA 0183) to shipboard display and sensor systems ( AIS Schematic). Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters.
Other information broadcast by the AIS,
Heading information and course
speed over ground would normally be provided by all AIS-equipped ships.
rate of turn,
angle of heel,
pitch and roll,
destination and ETA could also be provided.
The AIS transponder normally works in an autonomous and continuous mode, regardless of whether it is operating in the open seas, coastal or inland areas.
TYPES OF AIS Class A Ship borne mobile equipment intended for vessels meeting IMO AIS carriage requirement. Class B Ship borne mobile equipment provides facilities not necessarily in full accord with IMO AIS carriage requirements. The Class B is nearly identical to the Class A, except the Class B: · Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A) · Does not transmit the vessel's IMO number · Does not transmit ETA or destination · Does not transmit navigational status · Is only required to receive, not transmit, text safety messages · Is only required to receive, not transmit, application identifiers (binary messages) · Does not transmit rate of turn information · Does not transmit maximum present static draught |
ADVANTAGES
Collision avoidance
AIS is used in navigation primarily for collision avoidance.
Vessel traffic services
In busy waters and harbors, a local Vessel Traffic Service (VTS) may exist to manage ship traffic. Here, AIS provides additional traffic awareness and provides the service with information on the kind of other ships and their movement. Aids to navigation
AIS was developed with the ability to broadcast positions and names of objects other than vessels, like navigational aid and marker positions. These aids can be located on shore, such as in a lighthouse, or on the water, on platforms or buoys. The US Coast Guard suggests that AIS might replace RACON, or radar beacons, currently used for electronic navigation aids
Search and rescue
For coordinating resources on scene of marine search and rescue operation, it is important to know the position and navigation status of ships in the vicinity of the ship or person in distress. Here AIS can provide additional information and awareness of the resources for on scene operation, even though AIS range is limited to VHF radio range
Accident Investigation
AIS information received by VTS is important for accident investigation to provide the accurate time, identity, position by GPS, compass heading, course over ground (COG), Speed (by log/SOG) and rate of turn (ROT) of the ships involved for accident analysis, rather than limited information (position, COG, SOG) of radar echo by radar.