Dependency of Backscattering from Ocean Surface on Wind Direction by using Pi-SAR: Low wind speed case

摘要

The dependency of backscattering from ocean surface on wind direction under relatively weak wind speed (～5m/s) is analyzed using observation data with three directions of illumination by an airborne dual-frequency synthetic aperture radar (SAR) in the L- and X-bands. In the X-band, the dependencies of the NRCSs in the parallel polarizations show different features each other. The NRCS difference between up- and down-wind conditions depends on the incidence angle in the X-band HH polarization, though that in the VV polarization, the NRCS difference is almost zero. Moreover, the NRCS difference between parallel- and cross-wind conditions in VV polarization is greater than that in the HH polarization. Though the dependency of the NRCS in the L-band on the wind direction is smaller than that in the X-band, the NRCSs in the L-band cross polarizations under the cross-wind condition is greater than that under the parallel-wind condition. The polarization ratio (PR) in the X-band shows the dependency on the wind direction. The PR difference between up- and down-wind directions depends on the incidence angle as the incidence angle dependency in the X-band HH polarization. The dependency of the PR in the L-band on wind direction is also weaker than that in the X-band. The results suggest the possibility of ocean wind measurement using the polarimetric SAR in the X-band and/or using the dual-frequency SAR.