The Applicability of InSAR and LiDAR Remote Sensing Technologies in the Large-Scale Monitoring of Roadside Slopes and surrounding Structures

In the past, when assessing the stability of roadside slopes in mountainous areas of Taiwan, road maintenance and inspection personnel were often limited by steep terrain and vegetation cover. They could only observe damages on the road surface and sides instead of grasping the key points of landslides and disasters. Among them, Sandimen and Wutai located on Highway 24 in Pingtung repeatedly suffer from natural disasters, such as falling rocks, debris avalanche or subsidence of roadbed, after the strike of Typhoon Morakot whenever a typhoon, torrential rain or earthquake event occurs. The government therefore spent a lot of money on road maintenance works. In this area, we have combined topographic features identified from LiDAR-derived 1-m resolution DEM and large-scale ground surface deformation observed using the multitemporal InSAR technique (MT-InSAR) developed based on ALOS-2 / PALSAR-2 images collected between 2015 and 2022. Then Sections 29.5K and 34.5K are selected as the key study area of this investigation. The cumulative deformation results of these key slopes are: -80 mm at 29.5K from ALOS-2 imagery and -103 mm at 34.5K from ALOS-2. As for the section of 29.5K, from May 8, 2016 to December 4, 2016, the overall slope of the road was affected by several heavy rains and typhoons, among which the maximum rainfall on that day reached 303 mm; and the amount of deformation decreased by 16.7 mm; the average deformation of subarea block A decreased by 33.6 mm, and the average deformation of subarea block B decreased by 14.8 mm. As for the section of 34.5K, the overall roadside slopes were affected by several heavy rains and typhoons, among which the maximum accumulation of rainfall on that day reached 303 mm, from May 8, 2016 to December 4, 2016. The amount of deformation decreased by 13.7 mm. Our primary results demonstrate that the cumulative deformation and rainfall of these two key slopes show a positive correlation.