## 3 Dataset and Methodology
### Sentinel-1 DInSAR Applied to Dry Andes  
The Sentinel-1 is a two-satellite constellation of the European Space Agency (ESA). The first satellite, Sentinel-1A, was launched in April 2014 and the second, Sentinel-1B, in April 2016. Compared to older constellations, Sentinel-1 offers remarkable features that have notably widened the applications of SAR interferometry [62; 63]. Chiefly, Sentinel-1 assures continuity in worldwide acquisitions, with a revisit time varying between six and 24 days, depending on the place. Additionally the orbital tube has a diameter of 300 m, minimizing the baselines between images and hence, providing less noisy interferograms compared to other sensors like Envisat, ERS, and Cosmo-SkyMed. Finally, the Sentinel-1 data is freely available without any restrictions for use. These characteristics result in a reliable system that has changed the DInSAR paradigm, providing a new and powerful tool for monitoring purposes. Differential SAR interferometry consists of the exploitation of the phase differences between two SAR images of the same area acquired at different times or from slightly different positions [64]. The interferometric phase is directly related to the differences in the satellite-target travel of the radar signal. These differences include the movements of the target between both acquisitions. However, the identification of these movements is not always a straightforward process. The phase is also affected by other components, such as the differences in the weather conditions at the acquisition times, the distance between the acquisition positions, or noise. Moreover, it must be taken into account that the phase values are known modulus \(2\pi\), i.e., the real phase differences are wrapped in the interval \([-\pi,\pi]\). The process of recovering the real values of the phase, called phase unwrapping, is an ill-posed problem. This aspect limits the ability to measure relatively fast movements (1 m/year). This is key to interpreting the DInSAR data properly for displacement detection. The relation between phase difference and displacement is proportional to the wavelength of the SAR signal. A phase variation of \(2\pi\) between pixels of the interferogram corresponds to half a wavelength of relative displacement between the corresponding points on the ground [64]. In the case of Sentinel-1, which operates in C-band, this is equivalent to 2.8 cm. However, the displacements measured by DInSAR are always in line of sight (LOS), i.e., it measures the projection of the real displacement in the sensor-target line. This means that the real displacements are usually underestimated. Under favorable conditions of low atmospheric components and noise, it is possible to measure displacement between points up to one tenth or less of the wavelength. This corresponds to approximately 3 mm of LOS displacement [61]. In this work, we analyze the interferograms with short temporal baselines (6, 12, 24, and 48 days). This is done in order to maintain high coherence and thereby maximize the covered areas. Table 1 shows the minimum displacement rate that is detectable for these temporal baselines. For example, the minimum detectable movement in a six-day interferogram is approximately 17 cm/year, while in a 48-day interferogram, it is 2.2 cm/year. It is worth noting that these numbers must be taken as an approximation and they can change as a function of coherence and noise level. Establishing a maximum observable displacement value is a more complex task. The main reason for this is that it not only depends on the wavelength, but also on the random characteristics of the movement and terrain. However, a rough approximation can be arrived at by assuming that the maximum detectable movement is below half a wavelength (2.8 cm for Sentinel-1). This corresponds to 170 cm/year for the six-day interferograms to 21.3 cm/year for the 48-day readings. This work focuses on the detection of active periglacial phenomena, and not on the determination of their magnitude of displacement.