## 2 Test Site and Dataset  
### Test Site  
The test site selected to evaluate the performance of the proposed technique corresponds to the area of El Forn de Canillo (located in the geographical coordinates 42.5610 north latitude and 1.6018 western longitude), which constitutes one of the biggest landslides of the Andorran Pyrenees; see Figure 0(a). The landslide is composed of a sequence of slides and earth-flows with a complex structure, which affects an estimated mass of around 300 Mm\({}^{3}\). In this context, three major sliding units were identified in 1994 by [PERSON] [27]. The first one corresponds to a slide originated in the area of Pla del Gespit and Costa de les Gerqueres (see Figure 0(b)), located in the southwest of the landslide, which reached the foot of the hillside. A second unit originated under El Pic de Maians (see Figure 0(b)) reaching a height of \(1640\) m, and which overlaps with the previous sliding unit, closing in the Valira River valley. Finally, a new rotational slide with a lower extension originated on the hillside, known as La Roca del Forn (see Figure 0(b)), in the northeast side of the hillside, has been identified. The landslide originated due to a decompression phenomenon after the removal of the Valira Glacier, between the years \(13,000\) and \(16,000\) BP [27]. Throughout the years, the Valira River has been progressively eroding the base of the whole hillside mass without reaching the bedrock, thus originating the landslide [27]. Different observations accumulated during the last few decades have evidenced that the slide mass is still active today, with a residual displacement of few centimeters per year. Concretely, a local failure  
Figure 1: (**a**) General overview of the landslide of El Forn de Canillo; (**b**) landslide limits and location of the in-field monitoring network installed (Points S2 to S10). in the area, known as Cal Borro-Cal Ponet, located in the northeast extreme of the main body of the landslide, has been recently identified, showing a higher activity coinciding with periods of intense rains and snow melting [28]. In the year \(2000\), the Andorran authorities promoted several actions for the management of the risk related with the geo-hazard threats associated with landslides, rockfalls and debris flows in the Andorran Pyrenees. Some specific management plans were carried out for the monitoring of El Forn de Canillo. Between the years \(2007\) and \(2009\), a network of geotechnical devices, including inclinometers, rod extensometers and piezometers, was installed over the surface of El Forn de Canillo to characterize and understand the dynamics of the landslide. A total of 10 boreholes, referred to as _S2_ to _S10_ in Figure 1b and reaching a depth between \(40\) and \(60\) m, were drilled and equipped with this instrumentation. The measurements provided by these devices have been recently studied with the objective of locating the sliding surfaces and characterizing the displaced material [28]. Unfortunately, some of the boreholes did not reach the needed depth, and consequently, the installed devices did not work properly in some points. Nonetheless, the measurements and observations carried out evidenced that, in addition to a residual movement of the landslide main lobe of some millimeters per year, the most active part corresponds to the secondary landslide of Cal Borro-Cal Ponet, which, between May and June, \(2009\), registered a velocity up to roughly \(2\) cm/month [28]. Intense sudden rain events and snow melting were observed during this period. Only those inclinometers reaching the needed depth continue working to date. This is the case of the one referred to as _S10_, located in the maximum displacement rate area of Cal Borro-Cal Ponet, which will be employed to validate the PSI results obtained in this work. Finally, \(3\) GB-SAR campaigns carried out by the Institute of Geomatics (Spain) monitored a network composed of \(15\) corner reflectors over the area of Cal Borro-Cal Ponet.