The correct answer is D) Anemometer. An anemometer is the instrument used to measure wind velocity or speed. It is specifically designed to detect and quantify the movement of air, which is a crucial factor in maritime navigation and operations. The anemometer measures the force or speed of the wind, providing essential information for weather forecasting, vessel operations, and safety considerations. The other options are incorrect because they measure different environmental factors: A) Hydrometer measures the density of liquids, B) Psychrometer measures humidity, and C) Barometer measures atmospheric pressure, none of which are directly related to wind velocity.