## 3 InSAR Historical Review (ERS, ENVISAT, Sentinel-1)  
The main objective of the InTarsis project is to devise a ground stability monitoring system based on InSAR to improve Atalaya Mining's control over its environmental liabilities. The first step consists of characterizing the deformation field in the target area to establish the monitoring baseline. Therefore, we have conducted a historical review of the SAR data in the ESA archives to identify the main deformation patterns. We downloaded all available data for the study area from the ERS (1991-2003), ENVISAT (2002-2012), and Sentinel-1 (2014--present) constellations. All three ESA constellations follow the same strategy for continuous monitoring of the planet with global coverage at medium resolution using C-band sensors suitable for global mapping and monitoring of areas with low to moderate penetration. We analyzed 481 images from 1992 to 2017 with different acquisition geometries, ascending and descending, from all tracks and frames covering the area. Finally, for this review, and depending on availability and suitability, we have selected 3 datasets:  
* 39 images from ERS1 and ERS2, descending track-366 from 1992 to 2001. * 22 images from ENVISAT, descending track-366 from 2003 to 2010. * 33 images from Sentinel-1, descending track-154 from 2015 to 2017. The main reason for working with descending images at this step is that it is the most suitable geometry to study the affected zone in the Atalaya open-pit, which is the main target of this study. For processing these datasets, we applied the Advanced Differential Interferometric SAR technique (A-DInSAR) using the SUBSIDENCE-GUI interferometric software based on the Coherent Pixels Technique (CPT) (Figure 2) developed at the Polytechnic University of Catalonia (UPC) and DARES [10; 28; 29; 30]. This software allows the user to perform the full interferometric chain by generating the interferograms starting from the SLC product and calculating the time series by applying different approaches based on multilooked images (coherence-based) and full-resolution techniques such as the recently developed Temporal Phase Coherence [31]. We clipped a region of interest (ROI) of 10 \(\times\) 11 km around the mining zone and we selected a multilooking window of 3 \(\times\) 15 samples which results in a ground resolution of around 60 \(\times\) 60 m for the three satellite constellations. The processing parameters generated a network of interferograms for each constellation that are worth comparing (Figure 3). The interferogram network of ERS satellites covers 5 years of images from mid-1995 to the end of 2000, images producing very low-quality interferograms are discarded. The resulting number of images available is not very high, around 4 images per year with high temporal baselines (temporal difference between acquisitions) which causes temporal decorrelation. Besides this, the spatial baseline (the spatial distance between the two sensor positions when the SAR pairs are acquired) is very large and this will affect the quality of the interferograms and the measurement coverage. The Envisat's network of interferograms shows less dispersion in the spatial baseline, but very important gaps in the temporal baseline, especially between 2007 and 2010, causing loss of coherence and therefore big zones without results, especially in areas where changes in the surface have been more important at that period. And finally, the Sentinel-1 cloud for the selected period, 2015-2017, shows a spectacular improvement in both temporal and spatial baselines, which will provide excellent interprogram quality and measurement coverage. The narrow Sentinel-1 orbital tube makes the spatial baselines very small, between \(\pm\)100 m, which ultimately results in very consistent displacement measures [32]. This dataset Sentinel-1 compiles images every 24 days, which we think is a good comprise for this study, even though the revisit time is of 6 days since April 2016.