Speed Over the Ground (SOG) (SOG)

The magnitude of a vessel’s velocity relative to the Earth’s surface.

SOG is commonly derived by GNSS from successive positions or signal measurements and is paired with course over the ground. It differs from speed through the water because current and leeway alter ground movement, while wind affects it indirectly through vessel motion.

SOG can be unreliable at very low speed or when position data are degraded, smoothed or stale. It gives no direction by itself and does not state closing speed to another vessel, so the associated course, sensor status and time reference matter.