For this step a DEM is required, e.g., obtained by the SRTM mission. The Doris distribution contains the utility construct_dem.sh do download and prepare SRTM data (see Section C.2.12). The utility also outputs a figure of the final result (.ps format) and the lines needed for the Doris input file.
The DEM-assisted coregistration is not dependent on the correlation between the master and the slave image. Coregistration errors due to bad distribution or lack of useful correlation windows in the conventional method are therefore prevented. Furthermore, the coregistration improves in case of large baselines and strong topography. The improvement is especially significant in case of X-band data. An analysis of the performance of the implemented DEM assisted coregistration for various sensors is described in [1,11].