AIS course and speed verification requires manual checks, as built-in tests do not confirm sensor accuracy before broadcast. The officer of the watch must periodically check own-ship position, speed over ground and sensor information to ensure reliability.
AIS dynamic information includes course over ground (COG) and speed over ground (SOG). COG is supplied when the connected position sensor calculates it, while SOG is supplied by the connected position sensor. Poorly configured or calibrated position, speed or heading sensors may cause incorrect information to be transmitted, and COG or SOG may be unavailable.
MCA guidance distinguishes AIS target course and speed over ground from the course and speed through the water relevant to applying the COLREG. Collision-avoidance decisions should be based primarily on systematic visual and/or radar observations rather than AIS data alone. On a suitable display, received AIS motion data can support target tracking and calculations such as closest point of approach and time to closest point of approach, while remaining supplementary information.
