Directional analysis of SAR images aiming at wind direction

Currently, the retrieval of wind fields from synthetic aperture radar (SAR) images suffers from inadequate knowledge of the wind direction. State-of-the-art spectral analysis works fine on open seas, but is limited in spatial resolution. The method described here is based on the local gradients computed with standard image processing algorithms. It handles image features not caused by wind and can be applied to irregularly shaped regions. The new method has already been applied to many images from the European Remote sensing Satellite SARs and RADARSAT-1 ScanSAR, usually supplying reasonable wind fields. The spatial sampling most frequently used was 20 x 20 and 10 x 10 km(2). In some cases, samplings down to 1 x 1 km(2) were tested. This paper describes the local gradients method including the filtering of nonwind generated image features and gives some application examples.