## 5 Conclusions  
This study evaluated the features and field applicability of different deformation measurement methods--Distributed Strain Sensing (DSS), Uncrewed Aerial System (UAS), and Total Station (TS)--based on multiple years of experience in monitoring deformation for two roadside slopes. The two sites have varying conditions such as soil type, geographical locations, and weather conditions. From the comparative study, the following conclusions are obtained. The DSS-based method was the quickest and easy method to measure the deformation of the ground surface. The installation of measurement poles was easy. The measurement took typically an hour for one site and needed only one operator. The method was little impaired by vegetation or snow covering once the system was installed. Training an operator was easy. The remote control and remote measurement were possible in some models. However, the fiber optic cable of DSS might suffer from the activity of wild animals and low-temperature-related voltage drops from the batteries. In addition, the PVC posts driven into the ground were observed to be unstable due to shrinkage cracks which impaired measurement in highly plastic soils. Galvanized zinc pipes with a depth deeper than the frost depth and dry cracks might be more adequate for these soils. DSS used one long fiber optic cable; therefore, a damaged section anywhere in the system could disable the measurement after the damage point. To prevent this issue, installing redundant lines of DSS might be required. The UAS-based method offered fast surveying even for a large job site. It was flexible to various weather conditions, except for snow coverings encountered in this study and some strong wind. The method could measure the 3-D surface deformation for the entire area of interest (not just at discrete points) with unmatched high resolution, providing deformation images extensively and clearly. The result of the UAS-based method generally agreed well qualitatively with those of other methods. The method provided rational deformation data even for relatively thick (0.3 m) vegetation areas. Acquiring and maintaining the dedicated equipment, such as a high-quality UAS, UAS license, and specialized software, for the UAS-based method may be expensive. Moreover, it is recommended to have one drone operator and one highway safety crew member. Traditional TS surveying was a popular technique; however, this method can be challenging to reliably deploy on certain slopes given moisture and safety concerns. The method was a two-person task; however, the output and measurement effectiveness were not better than the DSS or UAS-based methods. It was, however, noted that the TS method could be the most economic for certain slopes, particularly when the number of measurement points are not very high. Due to the substantial differences in the measurement principles of the DSS, UAS, and TS, it was not possible to compare their errors directly. Nevertheless, these techniques are selectively preferred for their ability to remotely sense deformation, which is crucial for safety and operational purposes. Figure 11: UAS-based deformation profile of Highway 84 (From Spring 2019 to Spring 2021, Unit of the color bar is in m). The authors propose a potential for combining different techniques to improve monitoring capabilities. While UAS can quickly monitor large and remote sites, it may face limitations in adverse weather conditions such as snow and strong wind. DSS can complement UAS by enabling remote/real-time measurements that can be conducted in small intervals and capture direct quasi-subsurface movement through anchor poles, indicating soil movement not affected by weathering elements. Conceptualization, C.R.S. ; Methodology, C.R.S., R.L.W., N.G. and A.S.; Formal analysis, R.L.W. ; Investigation, B.B. ; Data curation, B.B. and N.G. ; Writing--original draft, C.R.S. ; Writing--review & editing, R.L.W., B.B., N.G. and M.N. ; Supervision, A.S.; Funding acquisition, C.R.S. and R.L.W.