## 5 Discussion  
### New Understanding of Landslide Development  
Understanding the development of landslides is critical for landslide hazard assessment as well as risk management. The results have shown that the InSAR technique is applicable to the identification of new landslides on the regional scale and can enhance the existing landslide inventory. Moreover, it would be of scientific significance to clarify how the newly identified landslides improve the understanding of landslide development in alpine forest regions. For this purpose, the statistic characteristics of the newly identified landslides by the InSAR technique and the landslide inventory established by field survey were compared in terms of frequently used landslide causative factors, namely altitude, slope, relief amplitude, distance to river, distance to road, and curvature of slope [70]. The results of the comparison are shown in Figure 13.  
As shown in Figure 13a, the landslides identified through field investigation are all distributed below the altitude of 3415 m. The InSAR technique not only reveals more landslides in almost all altitude groups than the field survey but also identifies 25 potential landslides at high altitudes (>3415 m), suggesting the advantage of the InSAR technique in detecting high-altitude landslides. A reasonable explanation for the difference is that landslides at high altitudes are difficult to identify through field investigations owing to the steep terrain and lack of road connectivity, while SAR satellites can easily capture high-altitude landslides with high accuracy. Recent studies support this explanation. For example, the Maoxian landslide and Baige landslide were missed in field investigations because they are located in a high-altitude region. However, they were clearly identified in post-analysis using InSAR techniques [31; 71; 72; 73]. Figure 12: UAV image showing the landslide phenomenon in the Chunchangba area. Regarding the slope distribution, the slope angles of the landslides were mainly concentrated in the range 20\({}^{\circ}\)-30\({}^{\circ}\) in both the InSAR-enhanced and field investigation results (Figure 13b), indicating that this slope range controls the development of landslides in the study area. Although the slope angles of both data sets showed similar distribution patterns, clear differences could be observed in the slope angle ranges of 20\({}^{\circ}\)-30\({}^{\circ}\) and 30\({}^{\circ}\), with the InSAR results showing larger numbers of potential landslides by 37.5% and 70%, respectively. In this manner, the InSAR technique enhanced the identification of potential landslides in the slope angle ranges of 20\({}^{\circ}\)-30\({}^{\circ}\) and 30\({}^{\circ}\)-40\({}^{\circ}\) at the regional scale. The relief amplitude refers to the maximum relative altitude difference within a certain distance in the landslide area, which was obtained through GIS analysis in this study. The search distance was set to be 100 m, which is the same as that in the analysis in Juzhaigou area by [PERSON] et al. [74]. As shown in Figure 13c, the relief amplitude of the potential landslide sites obtained through the field investigation mainly fell in the range of 45-58 m, while the InSAR analysis revealed significant increases in potential landslides in every relief amplitude bin, especially in the range from 58 m to 92 m. The dominant relief amplitude extended from the range of 45-58 m to 45-69 m, implying that the relief amplitude from 45 to 69 m controls landslide development in the study area and more attention should be paid to this range in future risk assessment. The distance to rivers is also a causative factor for landslide development as river water could erode the slope toe. Both the InSAR analysis and field investigation showed that landslide sites are mainly distributed within 500 m from rivers in the study area (Figure 13d) because toe erosion is more likely to occur at slopes close to the river.