Large-area landslide detection and monitoring with ALOS/PALSAR imagery data over Northern California and Southern Oregon, USA

a r t i c l e i n f o Multi-temporal ALOS/PALSAR images are used to automatically investigate landslide activity over an area of ~ 200 km by ~ 350 km in northern California and southern Oregon. Interferometric synthetic aperture radar (InSAR) deformation images, InSAR coherence maps, SAR backscattering intensity images, and a DEM gradient map are combined to detect active landslides by setting individual thresholds. More than 50 active landslides covering a total of about 40 km 2 area are detected. Then the short baseline subsets (SBAS) InSAR method is applied to retrieve time-series deformation patterns of individual detected landslides. Down-slope landslide motions observed from adjacent satellite tracks with slightly different radar look angles are used to verify InSAR results and measurement accuracy. Comparison of the landslide motion with the precipitation record suggests that the landslide deformation correlates with the rainfall rate, with a lag time of around 1–2 months between the precipitation peak and the maximum landslide displacement. The results will provide new insights into landslide mechanisms in the Pacific Northwest, and facilitate development of early warning systems for landslides under abnormal rainfall conditions. Additionally, this method will allow identification of active landslides in broad areas of the Pacific Northwest in an efficient and systematic manner, including remote and heavily vegetated areas difficult to inventory by traditional methods. Landslides are defined as the movement of a mass of rock, debris or earth down a slope (Cruden, 1991), and can result in enormous casualties and huge economic losses in mountainous regions. Additionally, landslides in the Pacific Northwest can damage habitat utilized by valuable fish species, such as salmon and steelhead. In recent years, many different mapping techniques have been implemented for the carto-graphic representation of landslide movement. These include landslide inventories, landslide displacement inventories, landslide hazard assessments , and landslide vulnerability assessments (Parise, 2001). Risk analysis and assessment have also become important tools in addressing uncertainty inherent in landslide hazards (Dai et al., 2002). In addition, susceptibility zoning involves the spatial distribution and rating of the terrain units according to their propensity to produce landslides (Fell et al., 2008). Among all of these studies, mapping landslide deformation is fundamental for the assessment and reduction of landslide hazards and risks. In comparison to the traditional investigation and reconnaissance methods, such as GPS, spirit leveling, tilting, optical remote sensing, geological and geophysical investigation methods, the interferometric synthetic aperture radar (InSAR) …