Abstract
The assessment of the natural hazards related to slow slope gravitational mass movements and to permafrost deformation is essential for the proactive management of the risk in the Alpine environment and for the relevant information on climate changes that can be derived from the study of the evolution of such phenomena. In this context, in the Alpine region, many kinds of landforms like rock and debris-covered glaciers or landslides can be affected by these phenomena. To this aim in-situ, proximal and remote sensing technologies can be used. In particular, Synthetic Aperture Radar (SAR) data and techniques have the surplus-value respect to other geodetic methods of providing information over distributed areas even at night-time and through the cloud cover.
Many new generation SAR techniques and data are available to monitor superficial deformations, but especially in the challenging mountain environments, the best solution for all these phenomena does not exist. This is due to the different characteristics of techniques (such as amplitude tracking, SAR simple- or multi-interferometry), data (in terms of wavelength, spatial and temporal resolution) and superficial deformations (which are characterized by different ranges, temporal evolutions, and seasonality behaviours, while the related areas of interest differ for size, steepness, spatial heterogeneity and soil properties).
This work considers two very different test sites characterized by superficial deformation phenomena located in South Tyrol (Italy): the Lazaun rock glacier and the Corvara landslide. However, in terms of analysis with SAR data, both present problems typical of mountainous areas. This makes possible to define and test criteria for the choice of SAR data and techniques.
The Lazaun rock glacier is situated in the southern Ötztal Alps (upper Schnals Valley, South Tyrol) and covers an area of 0.12 km2. The medium-sized active rock glacier extends from 2480 to 2700 meters a.s.l. and it moves downstream because of the deformation of internal ice. Very high-resolution TerraSAR-X images were used for Differential SAR Interferometry and amplitude tracking processing to monitor its displacement. Moreover, Sentinel-1 data were processed through the Small Baseline Subset technique and from the combination of both ascending and descending acquisition geometries it was possible to estimate the vertical displacement rate in the area of interest, identifying mass movements and other displacements related to the permafrost creep.
The Corvara landslide is located in Badia Valley with a surface area of 2.5 km2. Being a vegetated area, the installation of artificial scatterers allowed to measure the displacements occurred from 2016 to 2018 through the analysis of the amplitude of very high-resolution TerraSAR-X data. Moreover, the application of a multi-temporal technique of Differential SAR Interferometry to Sentinel-1 data permitted to monitor the landslide with extensive spatial coverage and to retrieve the displacement evolution of the area during the snow-free period.
GNSS, UAV and Ground-Based SAR campaigns in the first case and GNSS in the second one were used for comparison and validation of the results obtained from SAR satellite data.
Processing and analysis were conducted within the ALPSMOTION project funded by the Province of Bolzano Italy. It will also be described an unsupervised method to update the regional rock glacier inventory exploiting interferometric SAR coherence and based on Sentinel-1 data, to discriminate between moving and no-moving landforms over large spatial areas developed in this project.