In this chapter the processing of step M_SIMAMP is described, where the amlitude of the master image is simulated. This step requires an external digital elevation model (DEM) such as SRTM (Shuttle Radar Topography Mission) elevation data. This step can be performed optionally to simulate the master amplitude  and should be done after the M_CROP step. In the following step M_TIMING, the synthetic amplitude can be used to compute the absolute timing error of the master acquisition.
We compute the synthetic amplitude for a given master acquisition using orbital information and topographic data. SRTM can be used to obtain the topography in 3 arcseconds (Near global: 90 m. at the equator) or 1 arcsecond (USA only) resolution. The input DEM file must have the byte order of your platform in order to extract correct elevation value, see SAM_IN_FORMAT option for details. The DEM should be in the WGS84 system (same as the orbit ephemerides) The Doris distribution contains the utility construct_dem.sh to download and prepare SRTM data (see Section C.2.12).