AIS course and speed matter for target assessment, relative movement monitoring, and early recognition of close-quarters situations. The system transmits course over ground (COG) and speed over ground (SOG), which are supplied by connected position sensors when they calculate these values. This ground-referenced data is distinct from heading or speed through the water.
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. However, COG or SOG may be unavailable, and poorly configured or calibrated position, speed or heading sensors can cause incorrect information to be transmitted.
MCA guidance distinguishes AIS target course and speed over ground from the course and speed through the water relevant to applying the COLREGs. It states that collision-avoidance decisions should be based primarily on systematic visual and/or radar observations. Mariners must use this dynamic information to support situational awareness, not as a substitute for proper lookout or all available means of assessment.
