A radar scatterometer is like a specialised radar “flashlight”: it sends out microwave pulses, listens to the echoes from the ocean surface or land, and measures how strong those echoes are. The strength of the echo depends on how rough the surface is at centimetre scales and how that roughness is oriented, which in turn is strongly controlled by the local wind blowing over the sea, or by snow, ice, soil moisture, and vegetation on land.
