New, high-resolution space born sensors offer the possibility of near-real-time 3D Earth surface mapping. Acquiring and processing data rapidly and at low cost as well as being insusceptible to logistical problems or adverse weather conditions they offer great potential monitoring and managing natural disasters and emergencies. Satellite remote sensing data enable continuous observation of the Earth's surface with short acquisition and revisit times. It has been created for dual use and it is a cutting-edge system in the world of Earth observation. Generating data on a global scale, the system is devoted to providing products and services for environmental monitoring and surveillance applications, for emergency prevention and management, for defense and national security, and for scientific and commercial purposes. The accuracy level of DSM can achieve is strictly related to two fundamental steps needed to generate a DSM from a satellite stereo pair.