Landslide monitoring: use of multi-temporal DEMs derived from different techniques

The comparison of Digital Elevation Models (DEMs) is a powerful tool for Earth surface deformation studies in landslide area. The use of DEMs allows in many cases a full description of the process, while the classical geodetic ground-based measurements give a sampling of deformation field at a limited number of points. Digital Elevation Models can be obtained by means of several techniques like digital photogrammetry, laser scanning and GPS methodology with its different measurement approaches. These techniques were applied on the Rocca Pitigliana landslide located in the Emilia-Romagna Region (Northern Italy). GPS kinematic surveys were performed to obtain DEMs at low costs, short execution time and high accuracy (decimetre level). The digital photogrammetry allowed to enlarge the time and the spatial domain of investigation, providing also historical images with precision strictly depending on the scale of the images, ranging, in this work, from few centimetres to sub-meter level. The terrestrial laser scanning, in many cases, assured the description of restricted zones with very high spatial accuracy (few centimetres). DEMs internal precision is strictly related to the selected surveying method, to the operative working conditions and to the morphological features of the studied area. The requirements for GPS kinematic surveying are the satellite visibility and the capability of walking along the landslide; aerial photogrammetry can model with high accuracy only surfaces without vegetation and shadowing effects; the terrestrial laser scanning requires good weather conditions. The results of measurements performed on the Rocca Pitigliana landslide, in the last two years, and the comparisons among the different observation techniques are described