The Wind Scatterometer (WS) was an instrument on board the ERS-2 mission.
The WS instrument was designed to measure wind over the oceans by measuring changes in radar backscatter caused by the wind. It obtained information on wind speed and direction at the sea surface for incorporation into models, global statistics and climatological datasets. It operated by recording the change in radar reflectivity of the sea due to the perturbation of small ripples by the wind close to the surface. This was possible because the radar backscatter returned to the satellite was modified by wind-driven ripples on the ocean surface and, since the energy in these ripples increased with wind velocity, backscatter increased with wind velocity.
The ERS-2 mission was launched in 1995 and ended in September 2011.