Earth Observation for Landslide Assessment Vern Singhroy Canada Centre for Remote Sensing, Ottawa, Canada Hiroshi Ohkura National Research Institute for Earth Sciences and Disaster Prevention, Tsukba, Japan Nancy Glenn Idaho State University, Pocatello, Idaho, USA Abstract–This report provides a summary from the larger CEOS Landslide hazard team report, focusing on EO information requirements for landslide assessment. I. INTRODUCTION This paper summarizes the current and potential uses of Earth Observation (EO) data for landslide assessment. The main objective of the CEOS (Committee for Earth Observation Satellites) Landslide Hazard Team is to assess the role of EO data by improving our understanding of the causes of ground failure and suggesting mitigation strategies. Globally, landslides cause approximately 1000 deaths a year with property damage of about US $4 billion [1]. Landslides pose serious threats to settlements, and structures that support transportation, natural resources management and tourism. They cause considerable damage to highways, railways, waterways and pipelines. They commonly occur with other major natural disasters such as earthquakes), volcanic activity, and floods caused by heavy rainfall. In many cases, expanded development and human activities, such as modified slopes and deforestation, can increase the incidence of landslide disasters. A. EO Information Requirements for Landslide Mitigation The main contribution of EO data is to provide the morphological, land use, and geological detail to assist in determining how the landslide failed and what caused the failure. Where failure could occur can be addressed in a more regional geographic information system (GIS) analysis as a necessary first step in risk analysis. This is because the factors contributing to slope failure at a specific site are generally complex and difficult to assess with confidence. Landslide risk studies are still not very common. This is mainly due to the fact that it is very difficult to represent landslide hazard in quantitative terms related to probability over large areas. This is because landslides do not have a clear magnitude/frequency relation, as is the case for floods or earthquakes. Two distinct approaches can be used to determine the characteristics of different landslides from remotely sensed data. The first approach is to determine the number, distribution, type, character, and superposition relations of landslides using available remotely sensed data. The second approach complements the first one by measuring dimensions (length, width, thickness and local slope) along and across the landslides using imagery and topographic profiles (e.g. laser altimeter profiles). Where possible these dimensional data should be compared to any previous studies. With these approaches, it is possible to derive qualitative and quantitative parameters on landslides that are necessary for improved understanding of landslide processes. Detailed scales (1:5000 or better) are required during the site investigations aimed at providing reliable information for designing engineering control works needed to prevent or repair slope failures [2]. This will be particularly the case in urban or per-urban settings where public safety is the principal issue, or where the socio-economic consequences of potential landslide damage might be severe. Therefore, the scales required during the design of slopes are often larger than 1:2000, and the most commonly used scales may vary from 1:1000 to 1:500. In some cases, even more detailed scales are utilised. This level of detail would imply a sub-meter pixel spatial resolution of remotely sensed data. Therefore, the practical or operational use of the currently available EO data in engineering geology site-specific landslide investigations is considerably limited [3]. The improved resolution of the planned future sensors (3 m or better pixel resolution), however, should provide information sufficiently detailed for assessing the feasibility of slope engineering projects and for defining some preliminary design characteristics. Various methods have been used to produce landslide inventory maps. These maps are produced from the interpretation of stereo aerial photographs, satellite images, ground surveys, and historical occurrences of landslides. The final product gives the spatial distribution of mass movements, represented either at scale or as points. When multi-temporal airborne or satellite image analysis is included the inventory maps show landslide activity. Detailed slope information is essential for reliable landslide inventory maps. Currently, topographic maps and digital elevation data are used. Slope affects surface drainage and is an important factor in the stability of the land surface. Current research has shown that airborne and satellite InSAR techniques are being used to produce detailed slope information [4],[5],[6]. This allows a more accurate interpretation of slope morphology and regional fracture systems with topographic expressions. However, further research is needed in updating local slope information from suitable InSAR pairs using ERS1& 2 tandem, JERS-1 and RADARSAT-1. The large archive of SRTM data will assist in providing regional slope maps. 0-7803-7537-8/02/$17.00 (C) 2002 IEEE Preprint/Prétirage