PALSAR/PALSAR-2による潮目の検出

We compared a Phased-Array L-band Synthetic Aperture Radar-2 (PALSAR-2) high-pass-filtered image with Moderate Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) and Chlorophyll-a (Chl-a) images. The comparison with the MODIS SST images revealed that the positions of line-shaped bright (ridge) patterns in the image correspond to large SST gradients, i.e., SST fronts. The comparison with the Chl-a image revealed some local Chl-a maxima along the synthetic aperture radar (SAR) ridge patterns in the PALSAR-2 contrast image. To comprehensively examine the relationship between the SAR line-shaped bright patterns and the surface currents, we compared the time series of the PALSAR images with the high-frequency radar surface currents. We observed that the positions and strengths of the SAR line-shaped bright patterns generally correspond to those of the current shear, suggesting a general theory that convergence areas induced by a large current shear are brightly imaged through the modulation of ocean surface roughness. The SAR-derived line-shaped bright pattern thus indicates a current rip (shiome) characterized physically as the convergence of surface currents. The effect of background wind fields on the SAR line-shaped bright patterns was also investigated, using SAR-derived wind fields. The results indicated that the SAR line-shaped patterns are not identified under winds stronger than 10 m/s, even when the current shear is large.