## 3 Data and Methods
### Differential SAR Interferometry Displacement Time Series Generation  
DInSAR has become an increasingly popular methodology to monitor geomorphological activity in periglasical landscapes in the recent years [10; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45], especially since the availability of Copernicus mission Sentinel-1. For this study, we used cost-free and open-access C-band (wavelength = 5.6 cm) SAR data obtained by the Sentinel-1 satellite constellation providing a repetition rate of 6 days over Europe. In order to ensure a consistent time series, we limited our analysis to the time period, during which both satellites were available, starting from January 2017 until December 2021 covering 5 years of data. We collected all Single Look Complex (SLC) acquisitions in the IW mode with VV polarization (resolution rg \(\times\) az: 2.3 m \(\times\) 13.9 m) available at the Alaska Satellite Facility [72] from 4 orbits covering our study sites (descending orbits: 66-293 acq, 168-293 acq; ascending orbits: 15-286 acq, 117-291 acq). Each orbit was processed individually based on the following processing steps carried out using a semi-automated approach based on snappy (python wrapper for SNAP functionalities--version 8) by ESA and Pyrate (version 0.5) by GeoScience Australia. These preprocessing steps require a high-quality DEM. We used the SwissALT3D DEM by Swisstopo (resolution: 2 m) [73] for the study sites in Grison and the digital terrain model Tyrol by Land Tirol (resolution: 1 m) [74] for the Kaiserbergtal site. The processing started with the execution of the following steps in snappy: First, (i) the most recent orbit file was applied and (ii) the bursts of interest were split using separate areas of interest for the Kaiserbergtal and the Grison sites. Each scene was then (iii) coregistered to the nearest observation in time in the same orbit using Back Geocoding. (iv) The Enhanced Spectral Diversity correction was additionally used in cases in which several bursts needed to be processed. Afterwards, (v) the differential interferogram was calculated for the coregistered dataset, including the subtraction of the topographic phase using the previously mentioned high-resolution DEMs and then (vi) debrusted. In  
Figure 2: Flowchart of the study presenting five major parts of the methodology: **(i)** Generation of the Differential SAR Interferometry (DInSAR) displacement time series from Sentinel-1 single look complex (SLC) data. **(ii)** Decomposition of line-of-sight (LOS) displacement from ascending and descending orbit into horizontal East-West and vertical Up-Down displacement. Consecutively, elevation change and direction of movement are derived. **(iii)** Generation of reference data from orthophotos and UAV imagery to assess the accuracy of decomposed DInSAR displacement rates. **(iv)** Calculation of seasonal movement. **(v)** Correlation analysis of the spatiotemporal dynamics. order to maintain the highest possible resolution, we avoided the commonly used uniform Multilooking Operator (e.g., [34; 41; 42]) and applied instead (vii) a weak Goldstein Phase Filter [75] (alpha = 0.5, fft size = 64, window size = 7) to dampen the effects of outliers and decorrelated pixels, while keeping the original resolution of 2.3 m \(\times\) 13.9 m. The result was (viii) cropped to the individual study sites to reduce the processing time for the (ix) phase unwrapping carried out in snaph [76] using the Minimum Cost Flow algorithm (MCF). The resulting unwrapped phase information was then (x) projected to Cartesian coordinates at a spatial sampling of 5 m using the high-resolution DEM. The unwrapped interferograms were then screened and scenes with average coherence values below a certain threshold were excluded from further analysis. Visual inspection showed that a coherence threshold of 0.5 is suited best to exclude scenes with widespread decorrelation of the phase signal. These scenes were mostly acquisitions with changing snow cover conditions during autumn, winter and spring.