Bringing satellite winds to hub-height

Satellite observations of the ocean surface can provide detailed information about the spatial wind variability over large areas. This is very valuable for the mapping of wind resources offshore where other measurements are costly and sparse. Satellite sensors operating at microwave frequencies measure the amount of radar backscatter from the sea surface, which is a function of the instant wind speed, wind direction, and satellite viewing geometry.

A major limitation related to wind retrievals from satellite observations is that existing empirical model functions relate the radar backscatter to wind speed at the height 10 m only. The extrapolation of satellite wind fields to higher heights, which are more relevant for wind energy, remains a challenge which cannot be addressed by means of satellite data alone.

As part of the EU-NORSEWInD project (2008-12), a hybrid method has been developed, which combines the strengths of satellite winds and numerical modeling for offshore wind resource mapping. The vertical wind profile derived from numerical models is applied in order to bring the 10-m satellite winds and resource estimates up to turbine hub-height (~100 m).

The method is tested over a focus area in the North Sea where offshore mast observations are also available. The 100-m wind resource maps based on satellite and model data agree very well. The results are promising for the future utilization of satellite observations in support of numerical model simulations for pre-feasibility studies.