Scatterometers
What do they measure?
- Le Sea surface wind: speed and direction at a height of 10 metres
- Les Sea ice: concentration, drift
Principles of Scatterometer measurement (Credits Eumetsat)
Principles of measurement
Scatterometers are radars that send microwave pulses (frequencies from 0.3 GHz to 300 GHz, expressed as wavelengths: 1 m to 1 mm) towards the surface and measure the reflected energy. They depend on the roughness of the surfaces (the rougher a surface the more it will reflect in the direction of the radio wave's origin) and their dielectric properties. The greater the dielectric constant, the stronger the reflected energy will be. Thus, water is a strong microwave reflector. At sea, the roughness is directly related to the strength of the surface wind and allows the determination of its speed. The use of beams emitted in several directions allows us to determine the direction of the wind.
Winds on 28 August 2005 in the Gulf of Mexico with the very strong (and catastrophic) Katrina hurricane (Credits NASA/JPL)
Today's operational instruments
- Ascat on Metop A, B & C (Eumetsat, Europe)