Ground-Based or Air-Borne Imagery Surveys

Image analysis is a state-of-the-art, attractive field of survey and is potentially useful for slope monitoring. In this regard, this chapter reviews the recent use of image analysis with emphasis on its application to forecasting rainfall-induced landslides. Because this kind of landslide allows a very short time of a few hours from monitoring to decision on evacuation, the easy availability of resources and quick action are the key. The second key issue is visibility because the monitoring has to take place during heavy rain after dark. The third issue is the accuracy of displacement monitoring because the precursor displacement prior to a landslide is of the order of mm. From these viewpoints, it may be said that image analysis is useful for monitoring of gravity-driven slow landslide movement, but not relevant for the rapid movement of rainfall-induced landslides.