A radar scatterometer is an active, non-imaging remote sensing device with a real aperture operating in the microwave region of the electromagnetic spectrum. The main purpose of a scatterometer is the characterization of the surface backscatter properties, when a high radiometric accuracy is of interest and the spatial resolution is of secondary importance. There are scatterometers used in laboratories, in the field installed on masts, cranes or trucks, airborne (airplanes, helicopters) and spaceborne scatterometers circling the Earth in an orbit. Spaceborne scatterometers usually achieve a global coverage with a high repetition frequency. The basic principle of the scatterometer the accurate measurement the intensity of the returned radar echo from the Earth’s surface. Because of the speckle effect in radar echoes, a large number of independent observations are averaged.
Scatterometry (Earth observation using scatterometers) gained the attention of scientists towards the end of the 1960s when it was realized that the sea clutter observed by Second World War radar operators on their screens was not just any noise obscuring small boats and low-flying aircraft. It was in fact the signal backscatter from small ocean surface waves, comparable in dimension to the wavelength of the radar (in the order of centimetres).
The primary application of radar scatterometers is the measurement of near-surface wind vectors (wind speed and direction) over the ocean. These wind vector data are based on indirect measurements, where the wind vector is derived from the relationship between the backscattered power, the small-scale ocean surface roughness, and the local wind vector at the ocean surface.