3.2.2.1.4. Wind speed

Wind speed modulus as computed from Envisat data (GDR cycle 40). Since wind speeds higher than 20 m/s can not be measured reliably, the algorithm used at that time in Envisat data is making a plateau at 21 m/s (see Data Use case: Altimetry for extreme weather studies). The algorithm is computing on the whole Earth, even if the output is not meaningful outside ocean. This map is drawn using the Basic Radar Altimetry Toolbox

The backscatter coefficient can be related to wind speed. The model functions developed to date for altimeter wind speed have all been purely empirical. The model function establishes a relation between the wind speed, and the sea surface backscatter coefficient and significant wave height. A wind speed is calculated through a mathematical relationship with the Ku-band backscatter coefficient and the significant wave height, using the Vandemark and Chapron algorithm. The wind speed model function is evaluated for 10 metres above the sea surface, and is considered to be accurate to 2 m/s.