Thursday, March 20, 2008

What AIS Broadcasts

A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes:
MMSI number - unique referenceable identification
Navigation status (as defined by the COLREGS - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined)
Rate of turn - right or left, 0 to 720 degrees per minute (input from rate-of-turn indicator)
Speed over ground - 1/10 knot resolution from 0 to 102 knots
Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) RAIM processing is being used
Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
Course over ground - relative to true north to 1/10th degree
True Heading - 0 to 359 degrees derived from gyro input
Time stamp - The universal time to nearest second that this information was generated
In addition, the Class A AIS unit broadcasts the following information every 6 minutes:
MMSI number - same unique identification used above, links the data above to described vessel
IMO number - unique referenceable identification (related to ship's construction)
Radio call sign - international call sign assigned to vessel, often used on voice radio
Name - Name of ship, 20 characters are provided
Type of ship/cargo - there is a table of possibilities that are available
Dimensions of ship - to nearest meter
Location on ship where reference point for position reports is located
Type of position fixing device - various options from differential GPS to undefined
Draught of ship - 1/10 meter to 25.5 meters [note "air-draught" is not provided]
Destination - 20 characters are provided
Estimated time of Arrival at destination - month, day, hour, and minute in UTC