## 3 Methods  
A set of differential interferograms was first generated for each Sentinel-1 stack using a 180-day limit on the temporal baseline, 150 m on the orbital baseline, and a multi-look factor of 7 \(\times\) 2 pixels (Table 1). In doing so, the topographic phase was simulated and removed with the aid of the SRTM DEM. The resultant pixel spacing in ground-range is approximately 20 m.  
Each set of differential interferograms were processed separately utilizing two different InSAR approaches: the first using a conventional SBAS approach, following [PERSON] et al. [38]; and the second using the ISBAS approach. The ISBAS processing was undertaken using the Advanced Pixel System using Intermittent SBAS (APSISTM) method (developed by Terra Motion Limited), which is an implementation of the ISBAS approach of [PERSON] et al. [39], but with additional capability for higher resolution processing, full stereo InSAR analysis and the ability to simulate the imaging geometry--important when monitoring areas of extreme topography. The processing for the two approaches is almost the same, except that the SBAS processing considers only pixels with consistent coherence throughout the entire stack, whereas the enhanced ISBAS processing considers pixels that satisfy the coherence threshold in a minimum number of interferograms--in doing so, permitting the analysis of features that are intermittently coherent. The optimum interferograms threshold can be identified based on an empirical relationship between the standard error of the ISBAS velocity solutions and the number of interferograms [44]. In this case, the minimum number of interferograms for the ISBAS processing was set as 350 (see Table 1), meaning that the maximum standard error was expected to be 0.59 mm/year. Average velocities and time-series of ground motion for the entire period of SAR observations were then computed relative to a reference point (located at 38.320\({}^{\circ}\) N, 72.612\({}^{\circ}\) E) located on a mountain ridge 5 km north of Lake Sarez. The same reference point was used for each InSAR method, and it was assumed to be stable based on its location away from potentially unstable slopes and its high temporal coherence. Providing measurements at \(\sim\)20 m resolution, these ground motion products were computed for each satellite track in an attempt to maximise the potential to identify potential ground motion hazards in the Lake Sarez area. Geometric distortions occur in the Sentinel-1 imagery, which are generated by topographic features on the ground and are a consequence of the side-looking geometry and the SAR operational parameters (e.g., incidence angle). These manifest as areas of layover and shadow that essentially obscure measurement of the affected areas (Figure 2). These effects are not a consequence of the choice of the InSAR processing technique but are an inherent limitation associated with all InSAR methods. However, as alluded to above, the area affected by layover and shadow can be extensive in mountainous areas [7] and need to be excluded from any InSAR analysis [49]. As part of the processing, a full simulation of the SAR imaging geometry is performed using the SRTM DEM and the satellite orbit parameters. The output of this is layover and shadow masks that delineate the effect that the mountainous topography has upon the ability to monitor ground motion through satellite InSAR surveys. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Geometry**} & **Angle of** & **Max.** & **Max.** & **Multi-Look** & **Coherence** & **N\({}^{\circ}\) of Inter-** & **Interreogram** & **Reference Point** \\  & **Inclence at** & **AOI Centre** & **Baseline (m)** & **Baseline (days)** & **Range** & **Threshold** & **ferograms** & **Threshold** & **(lat/long)** \\ \hline Ascending & \(\sim\)37\({}^{\circ}\) & 150 & 180 & 7:2 & 0.45 & 710 & 350 & 38.320\({}^{\circ}\)/ \\ Descending & \(\sim\)35\({}^{\circ}\) & 150 & 180 & 7:2 & 0.45 & 701 & 350 & 72.612\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}