## 3 InSAR Utilizations in the Selected Literature Collection
### Development and Utilization of Spaceborne InSAR  
Over the past few decades, there has been a significant increase in the deployment and operation of SAR satellite platforms, reflecting substantial growth in both their numbers and capabilities (Figure 5a). SAR systems can be categorized by the increase of wavelength into the X, C, and L bands, with longer wavelengths providing enhanced penetration capabilities into vegetation and soil. Moreover, the spatial resolution of SAR imagery has seen marked improvements over the years, evolving from the coarse resolution of ERS-1/2, suitable for large-scale deformation measurement but limited in detail, to the high resolution exemplified by TerraSAR-X and COSMO-SkyMed.  
Out of the 80 selected research articles utilizing InSAR, Sentinel-1A/1B stands out as the most frequently used SAR data source, accounting for 52 studies (Figure 5b). This prominence is primarily attributed to its free and open data policy, high temporal resolution,  
Figure 5: (**a**) Major spaceborne SAR platforms over recent decades, along with their spatial resolutions and band types. The two red dashed lines represent the year 2013 and year 2023, respectively. (**b**) The proportion of different SAR data sources employed during this period. Notes: (1) The Sentinel-1B has stopped providing data since December 2021 due to a power issue. (2) As Sentinel 1A and Sentinel 1B are typically used together in most studies, the statistics are conducted based on the Sentinel-1 constellation as a unit. (3) Some studies may use more than one SAR data source. (Software: Origin 2022).  
and comprehensive and consistent global coverage, which make it highly accessible and practical for researchers worldwide. The launch of Sentinel-1B in 2016 and its pairing with Sentinel-1A reduced the revisit time from 12 days to 6 days, thereby facilitating more frequent monitoring of dynamic landslide processes. Envisat and ALOS-1/2 also feature prominently, reflecting their historical significance in studies requiring long-time series analysis or comparisons with historical data. Platforms such as TerraSAR-X, COSMO-SkyMed, and RADARSAT-2, although offering high-resolution imagery, are less commonly used due to data access restrictions and the costs associated with commercial data.  
To gain a more detailed understanding of the application of InSAR in landslide monitoring and susceptibility mapping, we classified the selected articles based on their research topics and whether InSAR was utilized (Figure 6). Landslide monitoring has consistently integrated InSAR throughout the entire period as it typically requires the measurement of surface deformation. For LSM, however, although InSAR was acknowledged and utilized in a limited number of studies prior to 2020, its prevalence has significantly increased in recent years, particularly between 2021 and 2023. This surge indicates the growing exploration of InSAR's capabilities in enhancing the accuracy and reliability of landslide susceptibility assessments, emphasizing the importance of a review to provide a comprehensive understanding of current advancements of InSAR in this field.