## 3 Methods
### Ground Motion  
For each InSAR method and track, the following ground motion products were generated at 20-m resolution: (i) the average line-of-sight (LOS) velocity for each pixel over the 2017-2019 period of observation; (ii) a time-series of ground motion throughout the same period of observation. The former assumes a linear model of deformation, whereas  
Figure 4: The coverage based on (**a**) combining the ascending and descending track geometries, and (**b**) the area common to both tracks. the latter determines the relative change in LOS displacement between each SAR image acquisition assuming a non-linear model of deformation. Ground motion is measured in the satellite LOS, which varies 29-46\({}^{\circ}\) from the surface normal across the swath from the near-to-far range. It should be noted that results from opposing geometries can appear to contradict each other. For example, the motion of an area of ground towards the satellite in the ascending data and might appear as motion away from the satellite in the descending data. However, this is simply a consequence of the side-looking geometry of the satellite, incidence angles, and steep topography (see Figure 5). The difference in coverage between the conventional SBAS method and the ISBAS method for the western part of the study area is illustrated in Figure 6. Owing to only sparse vegetation, both techniques provide reasonable coverage of measurements over the site and identify areas that appear to be in significant motion. However, there are some significant gaps in the coverage of the SBAS results when compared to the ISBAS survey. The coverage and measurement densities for the different approaches, excluding layover and shadow areas, are shown in Table 2. Providing more than double the spatial coverage, it is clear that the ISBAS survey is superior to the SBAS method in being able to provide ubiquitous coverage of all visible slopes in the Lake Sarez area. This concurs with the observations of studies in other regions (e.g., [44]) and can be attributed to the intermittent nature of coherence associated with land cover types, such as vegetation and snow cover, that vary over time. With this in mind, only the ISBAS results will be considered from this point onwards. Figure 5: Line-of-sight (LOS) motion on a west-facing slope viewed from opposing geometries. Should point A move downslope to point B between acquisitions, the ascending data would register a decrease in distance by an amount LOS\({}_{\text{asc}}\) whereas the descending data would identify an increase of LOS\({}_{\text{desc}}\). Owing to the imaging geometry, LOS\({}_{\text{asc}}\) < LOS\({}_{\text{desc}}\) meaning that the descending data is much more sensitive to changes. Figure 7 shows the ISBAS average velocities from both geometries, and it can be seen that the wider surroundings of Lake Sarez are very dynamic. In this figure, the blue colour indicates motion towards the sensor and red away. Additionally, in this case, the ascending geometry (Figure 7a) is viewing from the left and the descending (Figure 7b) from the right. With a few exceptions, the observed motion can be predominantly attributed to mass movements down the steep slopes. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Track** & **InSAR Method** & **Coverage (\%)** &
\begin{tabular}{c} **Average Measurement** \\ **Density (Pixels Per km2)** \\ \end{tabular} \\ \hline Ascending (N\({}^{\circ}\) 100) & SBAS & 44 & 1100 \\  & ISBAS & 100 & 2500 \\ Descending (N\({}^{\circ}\) 5) & SBAS & 35 & 875 \\  & ISBAS & 100 & 2500 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Coverage and density of ground motion measurements from the two tracks and InSAR methods across the study area, with areas of layover and shadow excluded. Figure 6: A comparison of the coverage between the SBAS and ISBAS methods for (**a**) ascending (track N\({}^{\circ}\) 100) and (**b**) descending (track N\({}^{\circ}\) 5) geometries for the western part of the study area. Layover and shadow areas have been excluded.