Landslide Activity Assessment of a Subtropical Area by Integrating InSAR, Landslide Inventory, Airborne LiDAR, and UAV Investigations: A Case Study in Northern Taiwan

Landslide, debris flow, and debris flood are the most common geological hazards triggered by intense rainfall in Taiwan. Taiwan is a very densely populated high relief island, and therefore the landslides sometimes affect our transportation and energy infrastructures and populated areas. This study investigates the regional landslide activity and potential slope movement using high-resolution time-series RADARSAT-2 InSAR images. We focussed on the 2015 typhoon, which affected Wulai and Xindian Districts in northern Taiwan. InSAR techniques, such as D-InSAR and SBAS, were applied to detect slope deformation caused by shallow and deep-seated landslides. This study conducted field investigations, and used high-resolution DTMs, and 3D photographic UAV surveying to determine the landslide hotspots and geomorphologic changes. The validation results show the InSAR maps accurately identify slow-moving landslides with a surface displacement of about 2 cm/year and debris flows on the bed of a gully. The InSAR displacement map helps to recognize the possible deep-seated landslides not previously known using a DTM. The field validation of the InSAR results from the proposed approach confirmed that the detection of different types of slope-land hazards: shallow landslides, deep-seated landslides, debris flows, and sediment deposition. Furthermore, the result will contribute to updating the national-wide environmental geologic map and provide competent authority to make decisions reducing the geohazard risk.