Evaluation of rock slope failure activity by comparison of multi-sensor InSAR datasets in the Sothern Swiss Alps

Spaceborne synthetic aperture radar interferometry (InSAR) is commonly applied in mountain environments to detect and monitor mass movements to support local or regional natural hazard evaluation. InSAR technology is being increasingly used thanks to the recent open data policies or relatively low costs. Despite the remarkable advantage of observing wide regions, the technology presents intrinsic limitations which are emphasized or reduced depending on the satellite and the characteristics of the area investigated. Satellites with different revisiting times and operating in various bands, namely in the X (wavelength lambda = 3.1 cm), C (lambda of 5.6 cm), and L (lambda of 23.1 cm) bands, are suitable for observing mass movements with different characteristics depending on mountain relief, vegetation, and displacement rates. However, the use of a certain satellite can result in misleading displacement rates or a lack of measurements.

In this work, we compare the data from different satellites to highlight the capabilities and the general limitations of the method for application in a 1’500 km² wide area of the Southern Swiss Alps, covering the Canton Ticino and a portion of Canton Grisons. The main valleys have a north-south orientation, characterized by steep slopes of altitudes between 2’000 and 3’000 meters a.s.l., covered by typical alpine vegetation. The dataset processed includes the ERS, Envisat, Sentinel-1, and RadarSAT missions, both ascending and descending geometries for a time frame of several decades. The distribution of the instabilities of the whole region is provided by the update “Catalog of the instabilities of Canton Ticino, 2016” expanded to the adjacent Calanca and Mesolcina valleys of Canton Grisons. The mapping has been made by the Institute of Earth Sciences of the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) in the framework of the Interreg AMALPI 18 project and the mapping of the geological maps Osogna, Grono, Biasca, and Mesolcina of the Swiss Geological Atlas AG25. We validate the InSAR results by comparing the surface velocities with terrestrial monitoring, field observations, and historical information that describe the rock slope failure activity.

From the statistical information obtained by the comparison of slope displacements detected through the Permanent Scatterers technique PS, the areas affected by instability, and different movement rates, we make considerations on the use of the PS for monitoring rock slope failures of different types and rates of displacement in a mountain context.