What does "speed over ground" (SOG) indicate?

Speed over ground (SOG) is a crucial concept in maritime navigation as it indicates the actual speed at which a vessel is moving across the Earth's surface, taking into account all factors, including current and wind. It measures the vessel's progress over a fixed point on land, effectively considering both the speed of the vessel itself and any external influences like currents or winds that may affect its trajectory.

When determining SOG, navigators utilize various tools and technologies, such as GPS, which provide real-time data that reflects how fast the vessel is traveling relative to the seabed or the earth's surface. This is particularly important for route planning, heading adjustments, and ensuring compliance with navigational regulations.

In contrast, the other options refer to different aspects of a vessel's movement. For example, the speed of water current affects the vessel but does not indicate its SOG, while the speed through water pertains to how fast the vessel moves in the water column, independent of any current. The average speed of the vessel over a period can give context but does not specifically define the SOG, which focuses on immediate spatial movement over the ground.