## 5 Conclusions  
The aim of this study was to evaluate the application of InSAR to remotely monitoring ground motion in high mountain terrain, where steep topography, variations in snow cover, and general inaccessibility combine to make conventional surveying extremely challenging. Using the Lake Sarez area in Tajikistan as a case study, two stacks of Sentinel-1 data from ascending and descending image geometries were processed, demonstrating that both surveys were severely affected by layover and shadow. Indeed, if focussing on areas that were mutually visible in both geometries, it was found that only 32% of the total ground area could be covered. The proportion of ground that was cumulatively covered by the geometries was much higher at 88%, and much higher than either the ascending or descending coverage alone, which was calculated to be 54% and 77%, respectively. If available, it is clear that both geometries should be interpreted separately to ensure the maximum possibility of identifying ground motion associated with geohazards in mountainous areas. This was also reinforced by the observation that neither of the geometries  
Figure 9: Time-series of ISBAS-derived cumulative LOS ground displacement for point B (indicated in Figure 6), the Usoy Dam. was singly able to identify all of the potential landslides whereas, in combination, the prospect was maximised. Regarding snow cover, the effect that even sporadic cover can have upon a conventional InSAR method could be severely limiting in achieving a detailed and comprehensive survey across the landscape. The Lake Sarez area is affected by variable snow cover in the winter months only, and then to an extent of only around 60%. This did not preclude the application of the APSISIM implementation of the ISBAS technique and, from the extent of the average motion maps and the time-series that were produced, did not appear to affect the results at all. Indeed, the method was shown to provide 100% coverage of the area not precluded by layover and shadow, which is more than double the amount possible using a conventional SBAS technique. While the coverage obtainable using an SBAS approach may be improved through careful selection of a temporal subset of SAR images not containing snow, the ISBAS method can be readily applied to the entire SAR stack due to its built-in consideration of intermittent coherence. The result obtained using the ISBAS method confirm the occurrence of ground motion across landslide areas identified in previous studies, agreeing in terms of the extent and direction of motion, and rates measured in the field and in previous InSAR studies. Importantly, this was achieved at high resolution (20 m) using freely available Sentinel-1 data, without recourse to any ground survey data, and without having to install corner reflectors or alike in the field. Notable areas of ground motion included the Right Bank (Pravoberezhniy) landslide, with rates of up to 105 mm/year. In contrast, the Usoy Dam was found to be stable overall, but with seasonal displacements of up to ~8 mm between spring and autumn. Monitoring high mountain terrain with EO data can be challenging, especially when using SAR data with an oblique viewing angle. However, as demonstrated here, extreme variations in topography, inaccessibility, and snow cover are not a barrier to the acquisition of dense measurements of ground motion as long as an appropriate InSAR method is utilised. Furthermore, an operational satellite mission acquiring data from ascending and descending geometries, such as Sentinel-1, with a good archive and a secure plan for the future provides a strong basis for a cost-effective routine remote and high-resolution monitoring system for geohazards in mountainous regions. Conceptualization, A.S. and S.G.; methodology, D.G., A.-A. and R.G. ; formal analysis, A.S., D.G. and A.A.; writing--original draft preparation, A.S., S.G. and B.D.I.B.-B. ; writing--review and editing, D.G., A.A., R.G., S.M. All authors have read and agreed to the published version of the manuscript.