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	DRS Direct Receiving Station Direct Receiving Station Direct Receiving Station

	DEM Digital Elevation Model Both digital terrain models (DTM) and digital elevation models (DEM) are files containing the altitudes of a region. Each point in the grid (every 20 m, for example) is attributed its altitude. The models are developed using stereopair imaging in particular, and are of great help in surveillance and monitoring operations, impact studies or choosing the best place to set up cellular phone networks. A DTM represents the theoretical surface on the ground while a DEM represents the theoretical surface of high points (such as tree tops).

	DTM Digital Terrain Model Both digital terrain models (DTM) and digital elevation models (DEM) are files containing the altitudes of a region. Each point in the grid (every 20 m, for example) is attributed its altitude. The models are developed using stereopair imaging in particular, and are of great help in surveillance and monitoring operations, impact studies or choosing the best place to set up cellular phone networks. A DTM represents the theoretical surface on the ground while a DEM represents the theoretical surface of high points (such as tree tops).