With moderate relief, the backslopes are geometrically distorted less than the foreslopes by a factor of 2 to 3. Also, backscatter from the backslopes is similar to that of standard look-angle incidence. If SAR images of the same surface, but from opposite look directions, are combined, then backslope backscatter information can be used to correct the erroneous foreslope information.
SAR images of the interior of Alaska acquired during ascending and descending orbits of the Earth Resources Satellite 1 (ERS-1) were geocoded and terrain corrected. These two images have look directions separated by about 140 degrees. The images were merged pixel-by-pixel by choosing the minimal pixel value which eliminates unusually high intensity values and, thus, chooses backslope values over brightened foreslope values. The minimal composition will reduce other sources of unusually bright pixels, such as speckle, since bright pixel values due to speckle are unlikely to occur in the same location in both images. To reduce dark and bright speckle as well as shadow, the images were also merged pixel-by-pixel by choosing the closest pixel values due to noise, anisotropy, or ephemeral events are reduced. The image becomes virtually distortion free and can be layered with any other geocoded and calibrated remotely sensed image.