Experimental tests on satellite and aerial stereo images for DEM extraction

In recent years research in the field of geometric correction of satellite data has reported remarkable methodological advances, implementing registration and ortho-rectifying algorithms which are now consolidated methods for the international scientific community. Generally, such procedures are carried out to correct or to eliminate image errors due to the bad functioning of sensors and to the atmospheric diffusion effects. Quality of data also depends on the intensity of spectral distribution of energy received by the sensor, with significant variations in its passage through the atmosphere. The automation and repeatability of the procedure on constantly updated data will permit the development of a monitoring system for land cover Transformations with environmental risk, not only to support preliminarily decisions in strategic planning contexts, but also as a tool to verify strategies and accomplishments, allowing modification of actions when the expected effects are not achieved. To detect and classify a landslide, it is necessary to view the size and contrast of the its features and the morphological expression of the topography within and around the landslide. Determining parameters are the type of movement that has occurred, the degree of present activity of the landslide, and the depth to which movement has occurred. The most common remote sensing tools used for the detection and classification of landslides are satellite imagery and aerial photography. Monitoring landslide movement involves the comparison of landslide conditions over time, including the aerial extent of a landslide, its speed of movement, and the change in its surface topography (i.e. DEM comparison) . The fundamental merits of the high resolution remote sensing are the ability to perform surveys at regular intervals in the operation, the characteristics of the image and the revisit times. These features are very useful in environmental monitoring especially in case of emergency or also in medium scale cartographic production, particularly in the zones of difficult access and in developing countries. The satellite Ikonos, is able to acquire images in stereopair with two different perspectives, during the same orbital transit and with a rivisit time of 3 days for every point on the terrestrial surface and it can effect two-way scannings and acquire up to 7 crawled adjoining strips (each of around 11-13 kms) in a single step.