Removing Automatically the Ambiguity in Wind Direction Retrieved from SAR Images

The evaluation of the wind resource in large areas to study the viability of wind farms is ideally studied using synthetic aperture radar (SAR) images in which the direction of the wind can be mapped from its effects on the water surface. Methods in use usually assume a fixed direction from a measurement for the whole image or interpolate the direction of wind fields from numerical weather models, that can be non-coincident in time with the SAR snapshot and of much less spatial resolution. The problem remains in the directional ambiguity of 180 degrees. This work presents three indexes to identify and validate initial “anchor vectors” that could be used as an aid in the complex process of remove this ambiguity, using wind shadows in the water near the coastline. These indexes consider several hypotheses to provide for local variability such as physiographic accidents, the eccentricity of the shadows and the effect of bay-shaped areas, all quantified through image processing methods. Comparing the results with the reference wind field provided by ESA for the time of acquisition of the ENVISAT-ASAR image used we could conclude that this is a promising line of work