Combination of interferograms from ascending and descending orbits

SAR interferometry can be usefully exploited for generating elevation maps. A problem derives from the image deformation due to the SAR geometry. As the terrain slope along range approaches the off-nadir angle (foreshortening areas), no elevation information can be extracted. However, if ascending and descending passes are considered, terrain coverage is increased. Those areas affected by foreshortening in one image are well covered (if not in shadow) in the other image.