We analyzed airborne L-band Synthetic aperture radar data from the Pi-SAR-L2 platform to detect agricultural fields in semi-mountainous areas of Japan. Full-polarimetric data were acquired during the rice growing season after transplanting. We examined the usefulness of single look complex and ortho-rectified data products by attempting polarimetric decompositions for the single look complex data and examining ortho-rectified images to evaluate image distortions and match these to map coordinates. The three component decomposition images show obvious differences between paddy rice and other fields; the former generally show low backscattering while other crop fields show a larger surface scattering component. Agricultural parcels with an area more than 3,000 m2 are clearly recognized on the ortho-rectified image, though narrow agricultural fields in valleys were missed due to the effects of foreshortening.