1. A method for orthocorrecting a satellite-acquired image, including distortion modeling for making positions of pixels in a corrected image and positions of pixels in an observed image correspond to each other and also resampling for interpolating intensities of said pixels in said observed image in accordance with results of said distortion modeling, wherein said distortion modeling comprises the following steps: (a) setting a plurality of control planes of different elevations relative to a control plane of a zero elevation of a reference rotating ellipsoidal earth model; (b) dividing said corrected image into plural blocks by lattices of equal intervals; (c) determining, with respect to each of said pixels in said corrected image, a corresponding one of said blocks; (d) determining two of said control planes, said two control planes sandwiching an elevation value of said position of said pixel above and below said elevation value in the thus-determined block; (e) calculating two pixel positions in said observed image, which correspond to said elevation value of said pixel position in said block, by using respective distortion model formulas determined as bilinear functions with respect to said two control planes; (f) linearly interpolating the thus-calculated two pixel positions by said elevation value of said pixel position in said corrected image to determine said pixel position in said observed image, which corresponds to said pixel position in said corrected image; and (g) repeating said steps (c) to (f) until pixel positions in said observed image are all determined corresponding to said individual pixel positions in said corrected image.