## 4 Measurement and Results/Discussion
### I-180 Slope  
One of the results depicted in Figure 9a illustrates the overall deformation measured by the DSS, situated just below the crack location in Figure 5a. This measurement accounts for the average strain multiplied by the length between anchor poles. Notably, this output indicated substantial movement at the toe of the slope that was imperceptible to the naked eye. Subsequently, during field reconnaissance on 26 April 2019, a pot-belly-like deformation was observed in segments 6 through 10, which qualitatively confirmed the findings presented in Figure 9a. This measurement result is notable considering that the slope was actually visually identified to have failed in May 2019. It is worth mentioning that the measurement between 9 November 2018, and 17 January 2019 could not be obtained due to unstable readings from the device. Although the exact cause was not determined, the research team speculated that the extremely cold temperature during that period may have contributed to the issue. Moreover, it was observed that the fully charged lithium-ion battery showed 12.7 V in the laboratory exhibited less than 11 V while in the field. While a drop in voltage of this magnitude is typical for lithium-ion batteries in cold weather, it may affect the performance of sensitive equipment. The measurement readings resumed on 17 January 2019 and persisted until 25 April 2019. However, in May 2019, the slope experienced significant movement, and the measurement readings were discontinued. For the TS-based results, the vector square root sum was applied to the deformation (in three dimensions) obtained from the total-station-based surface survey, shown in Figure 9b as a two-dimensional plot. The magnitude of deformation shown in Figure 9b includes the deformation that occurred from the failure in May 2019. The figure shows a sharper deformation gradient towards the north, where a substantial vertical drop and opening were observed. At the downslope side, the deformation is approximately 7 cm, which is lower than that measured by the DSS. However, it is noted that DSS-measured deformation is the relative deformation between anchor poles, not the total deformation. It is also noted that the DSS-measured deformation data may be affected by the temperature, especially during extremely cold weather. Therefore, in this study, DSS data were not corrected for the temperature, nor edited to show the total deformation, due to the lack of science/engineering for clearly separating the effect of temperature from DSS-measured  
Figure 9: Deformation profiles of I-180 slope obtained from different methods. (**a**) Downward deformation monitored by DSS. Note: (100 mm = 2.5% downward strain) (**b**) Deformation (m) contour measured by TS (Difference between before and after the failure. Arrows indicate the direction of the movement). (**c**) Deformation profile from the UAS-based method (Unit of the color bar is in cm). deformation installed between semi-rigid anchors. Therefore, a direct comparison of the deformation magnitude of the survey and that of DSS was not conducted. UAS-based deformation surveying is based on the multiscale cloud comparison (M3C2) algorithm within the CloudCompare software, as developed by [PERSON] et al. [31]. This algorithm finds differences between two-point clouds (at different time periods) by calculating the average distance of matching points. This algorithm is point cloud-based; therefore, it has fewer geometry-related errors. Because of this feature, the M3C2 method has gained popularity in recent years, as addressed in [PERSON] et al. [32] and [PERSON] et al. [33]. In this study, the point clouds of the site are compared against each other from Spring 2019 to Spring 2021. A UAS-based method in Figure 9c shows concentrated deformation along the failure line (shown in bright green). Some areas are impeded due to the presence of heavy vegetation and no data appear in these regions (white spots).