Comparing Satellite Based and Ground Based Radar Interferometry and Field Observations at the Canillo Landslide (Pyrenees)

The landslide of El Forn de Canillo in the Principality of Andorra is one of the largest in the Pyrenees. In 2007 a monitoring system (boreholes equipped with inclinometers, extensometers and piezometers) was set up. Between 2010 and 2011, surface displacements were measured using differential interferometry techniques (GB-SAR and DInSAR). The interferograms of both radars have yielded mutually consistent results, compatible with the inclinometric measures. Furthermore, the observations with TerraSAR-X, with greater spatial coverage, have shown that the displacements are significantly higher in the upper part of the slope (up to 4 cm/year). Field surveys evidenced the presence of activity indicators (open tension cracks, ground disturbance and structural damages) that confirm the existence of these movements. In El Forn landslide, the combined use of radar techniques with conventional instrumentation allows for a more complete and representative interpretation of the behavior of the slope.