Mapping of mesoscale wind fields using RADARSAT-1 ScanSAR images

Abstract

The availability of cloud- and light-independent synthetic aperture radar (SAR) data provides a perspective of the ocean surface that is unique in satellite remote sensing. The high spatial resolution and large coverage of satellite-based SAR offer the opportunity to derive mesoscale wind fields over the ocean surface with spatial resolution nearly 2 orders of magnitude higher (500 m) than conventional scatterometers (45 km). This enhanced resolution gives new opportunities for quantitative analyzes of marine atmospheric boundary layer and oceanographic processes especially in coastal areas. In this paper an algorithm is developed and tested to retrieve mesoscale wind fields from the ScanSAR aboard the Canadian satellite RADARSAT-1, which operates at C-band with horizontal polarization in transmit and receive. Wind directions are extracted from wind induced streaks visible on most SAR images by visual inspection and spectral filtering of the image power spectra. Wind speeds are derived from the normalized radar cross section (NRCS), image geometry of the images, and wind direction by inversion of semi empirical C-band models which describe the dependency of the NRCS on wind. The models were specially developed for the scatterometer aboard the European remote sensing satellites ERS-1 and ERS-2, which operates at C-band with vertical polarization in transmit and receive. To apply these models to ScanSAR data they have to be modified for horizontal polarization, which was performed considering several C-band polarization ratios including theoretical and empirical forms.