Digital elevation are frequently obtained by remote sensing rather than direct survey. These can be prepared in a number of ways,but one of the powerful technique for generating digital elevation model is interferometric synthetic aperture radar: two passes of a radar satellite (such as RADARSAT-1), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), suffice to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.
A digital elevation model (DEM) or digital elevation modeling is a digital representation of ground surface topography or terrain, thus also widely known as a digital terrain model (DTM) or digital terrain modeling. A DEM can be represented as a raster , a grid of squares or as a triangular irregular network. digital elevation models are commonly built using remote sensing techniques, but they may also be built from land surveying. DEMs are used often in GIS, and are the most common basis for digitally-produced relief maps. DTM DEM generation is commonly used in remote sensing gis.