The Wind Scatterometer (WS) was an instrument onboard the ERS-1 and ERS-2 missions.

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 WS worked in tandem with the Synthetic Aperture Radar (SAR) instrument in a configuration called the 'Active Microwave Instrument' (AMI). The AMI was operated in either SAR or Wind mode but could also operate in a combined mode - wind/wave mode which consisted of Scatterometer operations (Wind mode) interrupted every 30 seconds (roughly 200 km) by a couple of seconds of a short SAR operation in order to acquire small SAR images of roughly 6 x 6 km from which wave spectra could be derived.

The ERS-1 mission launched on 17 July 1991 and ended on 10 March 2000, ERS-2 was launched on 21 April 1995 and retired on 5 September 2011.