A DIGITAL CLOSE-RANGE PHOTOGRAMMETRIC TECHNIQUE FOR MONITORING SLOPE DISPLACEMENTS Efstratios Stylianidis , Petros Patias , Vassilios Tsioukas , Lazaros Sechidis and Charalambos Georgiadis Aristotle University of Thessaloniki, Department of Cadastre, Photogrammetry & Cartography University Box 473, GR 54006 Thessaloniki, Greece Abstract Deformation monitoring of slope instability and its surroundings supplies important information on the behavior of the slope in that it evaluates whether potential collapse may occur. Monitoring results may also be used in verifying design geotechnical parameters of slopes such as in mines and aid in the calculation of soil mass volume. The development of digital Photogrammetry allows calculation of high accuracy three-dimensional coordinates for points on and around the slopes. A main advantage is that no physical contact with the monitoring body (i.e., to install targets) is necessary, like in conventional land surveying techniques. Given the high spatial resolution of Photogrammetry compared to discrete point monitoring of conventional surveying, it is evident that there is enormous potential for use of this technology in monitoring applications where dense data sets could provide great insight into the nature of slope displacements for risk assessment, volume computation and structural model validation. The paper describes the use of digital Photogrammetry in the slope monitoring and soil volume computation under real conditions. The proposed technique uses digital close-range photogrammetric images and non-signalized control points. The advantage in this approach is that the data processing is applied in a terrestrial photogrammetric coordinate system, i.e. xy- plane in a vertical position, but the products can be generated in a standard 3D Cartesian coordinate system (horizontal xy-plane) as well. Finally, results including 2D maps, orthomaps, 3D photorealistic views and the calculation of the moving soil mass volume are presented. 1. Introduction Digital close-range Photogrammetry is a measurement technology which is used to acquire 3D spatial information about an object that is captured on the images. By this means, this technology derives measurements from digital images, rather than measuring the object straight. Photogrammetry offers several advantages over the conventional and well-known land surveying methods. First, it is possible to map objects that are unreachable or too dangerous to reach on foot. Second, Photogrammetry provides a flexible framework in that all data needed to perform the mapping can be achieved almost immediately, enduringly and at a permanent cost with one photographic acquisition. Mapping process can then be implemented at any time thereafter. Cost effectiveness may refer as a third advantage of Photogrammetry in contrast to conventional surveying or geodetic techniques. Finally, Photogrammetry provides several kinds of digital products such as maps, digital elevation models and orthoimages. Due to this capability, digital close-range Photogrammetry is appropriate for a variety of applications, ranging from industry to archaeology, monitoring issues (Kersten and Mass, 1995) etc. The paper reports on how to use digital close-range photogrammetric techniques in monitoring slope displacements. The most intriguing issue in this approach is that the data processing is obtained in a terrestrial photogrammetric coordinate system, i.e. xy-plane stands in a vertical position, nevertheless the products could be generate in a standard 3D Cartesian coordinate system (horizontal xy-plane) as well. Proceedings, 11 th FIG Symposium on Deformation Measurements, Santorini, Greece, 2003.