Application of Unmanned Aerial Vehicle (UAV)-Acquired Topography for Quantifying Typhoon-Driven Landslide Volume and Its Potential Topographic Impact on Rivers in Mountains Catchments  
[PERSON]  
1 Department of Civil Engineering, National Taipei University of Technology, Taipei 10608, Taiwan; [EMAIL_ADDRESS] (K-J.C.); [EMAIL_ADDRESS] (C.-W.T.); #[EMAIL_ADDRESS] (T.-C.L.)  
[PERSON]  
2  
[PERSON]  
3 Department of Land Management and Development, Chang Jung Christian University, Tainan 71101, Taiwan; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Civil Engineering, National Taipei University of Technology, Taipei 10608, Taiwan; [EMAIL_ADDRESS] (K-J.C.); [EMAIL_ADDRESS] (C.-W.T.); #[EMAIL_ADDRESS] (T.-C.L.)  
[PERSON]  
4  
Correspondence: [EMAIL_ADDRESS]; Tel.: +886-2-3366-5825454  
and timeliness/completeness of satellite image acquisition; therefore, it is not feasible to conduct a comprehensive survey immediately after a typhoon event.  
Progressive development of structure-from-motion (SfM) photogrammetric techniques and Unmanned Aerial Vehicles (UAVs) [15; 16], which provide low-cost and high-resolution digital elevation models (DEMs) can be constructed using remote-controlled UAV surveys. Additionally, UAV-driven images can be corrected using ground control points, such as data from light detection and ranging (LiDAR) and real-time kinematic Global Positioning System (RTK-GPS), which can then be given high-precision spatial information [17; 18]. UAVs can be applied to many fields such as disaster relief [19; 20; 21], studies of active tectonics [22; 23; 24], and studies of fluvial processes [25; 26; 27]. The advantages of the extensive, fast image acquisition capability provide a great opportunity to map landslides in mountainous river regions [28; 29; 30; 31; 32].  
Typhoon Morakot in 2009, induced precipitation of 2686 mm in three days in Pingtung County and 2517 mm in Kaohsiung City [33], causing severe landslides in the mountainous areas of southern Taiwan [34; 35; 36]. Among the landslide-affected areas, the Laonong River catchment had the largest landslide area and the highest new landslide ratio [37]. Meanwhile, the upstream regions of the Linbian River, Laishe River became potential debris flow source areas, which continue to experience landslides. The threat of landslides not only affects the economic production, lives, and safety of mountain villages, but also affects the ability to preserve ecological resources and to conserve soil and water resources. Undoubtedly, the Laishe River catchment is one of the most highly landslide-affected areas after Typhoon Morakot. Therefore, it may provide an opportunity to examine the applicability of UAVs in quantifying the typhoon-derived landslide volume of the mountainous catchment. In this study, the images Digital Mapping Camera (DMC), of ADS40, LiDAR, and UAVs are integrated to decipher the consequences and the potential hazards. This study constructs DEMs before and after Typhoon Morakot, as well as the subsequent periods. With the datasets, it is possible to quantify the landslide volume and conduct further analysis of the morphological changes in the Laishe River catchment. The result can provide not only the geospatial dataset of the hazards, but also the essential geomorphologic, hazard mitigation, and planning information.