Proceedings, Slope Stability 2011: International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Vancouver, Canada (September 18-21, 2011) A GIS Tool for Objective Suitability Evaluation of the Differential Radar Interferometry Method for Deformation Monitoring of Landslides S. Plank Technische Universität München, Chair for Engineering Geology, Munich, Germany J. Singer Technische Universität München, Chair for Engineering Geology, Munich, Germany C. Minet Remote Sensing, German Aerospace Center (DLR), Oberpfaffenhofen, Germany K. Thuro Technische Universität München, Chair for Engineering Geology, Munich, Germany Abstract Differential radar interferometry (D-InSAR) is a powerful remote sensing technique for detection and deforma- tion monitoring of landslides. However, as a consequence of the radar specific imaging geometry spatial distor- tions, such as the layover and shadowing effect occur in the radar image, which have a negative impact on the suitability of the radar images for D-InSAR applications. Therefore we present a GIS-routine to accurately predict the areas which will be affected by layover and shadowing, before recording the area of interest by radar. Furthermore, the measurable percentage of movement of a potential landslide can be determined. The main types of land cover are classified in regard to the applicability of the D-InSAR-technique, depending on the characteristics of the sensor used. These analyses allow stakeholders without expert knowledge of the D-InSAR- method to objectively evaluate the applicability of the D-InSAR-technique for landslides on a detailed, site specific or regional scale. 1 Introduction Using the active remote sensing technique differential radar interferometry (D-InSAR) it is possible to detect and measure deformation of the Earth’s crust, such as landslides, with an accuracy of a few millimetres. The illumination of the Earth’s surface by the air- or satellite-borne radar sensor is done obliquely downward, perpendicular to the flight direction (azimuth). The radar sensor measures the duration of a pulse to determine the position of an object on ground. The apparent distance between two points on ground depends on the difference in arrival times of both reflections on the sensor. This way to acquire data causes spatial distortions in radar images – especially in areas with a topographic relief (where landslides usually occur). Due to the lateral illumination of the Earth’s surface, certain areas, for instance behind steep mountains, are not achieved. These areas are in the shadow of the radar (shadowing). The satellite gets no information of these areas. Therefore the D-InSAR technique cannot be used in such areas. In hilly terrain slopes leaning towards the sensor are shortened in the radar image (foreshortening). This effect is caused by the shortening of the radar signal runtime, as the distance from the sensor to the surface is shortened by the inclination of the slope. Thus, the elevated points move closer to the sensor and the slope appears shortened in the radar image. An extreme type of foreshortening is the so-called layover effect. It occurs in very steep terrain. In such areas the pulse of the radar beam hits several objects on ground at the same time (e.g. the summit of a mountain and a point located in a valley in front of the mountain). Consequently these points are imaged as one pixel in the radar screen. In layover areas there is an overlap of information coming from different positions on ground. Therefore in areas affected by layover, the D-InSAR method can also not be used. (Barbieri & Lichtenegger 2005, Lillesand & Kiefer 2007). Beside these geometric distortions, the land cover has great influence on the applicability of differential radar interferometry. For D-InSAR applications areas with a high constancy of their backscattering properties are necessary. Variances on ground in the time between the two radar recordings (e.g. caused by plant growth and movements of trees due to wind) lead to changes of these backscattering properties.