Fast Rectification for Space-borne Sar Digital Images with No Ground Control Point

In this paper, a fast geometric rectification method for space-borne SAR (Synthetic Aperture Radar) digital image in slant range with no ground control point is introduced , which is based on the imaging principle of SAR and the law of geometric distortion in slant range image. The main idea is at first to resample a slant range SAR image to a ground range image with a definite ground spacing because the ground spacing corresponding to each pixel in slant is different caused by the different view angle. The coordinate system of the resampled image can be recognized as a plane rectangular coordinate system formed by the flight direction and the ground range direction. For the plain areas, the ground range image can be transformed into the image in a projected geographic coordinate system by four corner points whose ground coordinates can be calculated by the imaging equation. The rectified image is obtained with high accuracy; While for the areas with fluctuation topography , a higher precision rectification can be made based on the ground range image for it maintains the information of the original SAR slant range image(ground range and flight height).