In an ERS-SAR image of the sea off Kii Peninsula on 30 March 1996, we found an atmospheric front formed by the sheltering effect of land topography and swell modulation in the sheltered/non-sheltered areas. From the SAR image, high-resolution wind speed and SAR-wave spectrum are retrieved. In the frequency range higher than the peak frequency, the SAR-spectra of the non-sheltered area have energy density higher than that of the sheltered area. The difference between the spectra of sheltered/non-sheltered areas is well explained by the simulated SAR spectra using the SAR-derived winds and a wind wave development formula suggest that the observed swell modulation is caused by the surface wind. This is a preliminary report and a full paper will appear elsewhere.