WiSAR a Tool for Operational Wind Field Retrieval from Synthetic Aperture Radar Data
Jochen Horstmann(1) and Wolfgang Koch(1)
GKSS Research Center,
WiSAR, a methodology for retrieving high resolution ocean surface wind fields from satellite borne synthetic aperture radar (SAR) data is introduced and validated. The algorithms developed are suited for ocean SAR data, which were acquired at C-band of either vertical (VV) or horizontal (HH) polarization in transmission and reception. Wind directions are extracted from wind induced streaks that are visible in SAR images of the ocean at scales above 200 m. These wind streaks are very well aligned with the mean surface wind direction. To extract the orientation of these streaks an algorithm based on the extraction of local gradients is introduced. Ocean surface wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local SAR-retrieved wind direction. Therefore, several C-band models (CMOD IFR2, CMOD4, and CMOD5) are available, which were developed for VV polarization and have to be extended for HH polarization. To compare the different algorithms and C-band models as well as demonstrate their applicability, SAR retrieved wind fields are compared to numerical model results considering advanced SAR data from the European satellite ENVISAT.