Using radar data from ESA’s Envisat, ERS and Copernicus Sentinel-1 satellites, scientists have shown how satellite radar interferometry can shed light on landslide processes in the Swiss Alps. 

Populations residing in mountainous regions are under constant threat of geo-hazards, such as slope instability and rock falls. Understanding how these processes evolve over time can help estimate the hazard and support civil protection strategies. 

A research collaboration between two Swiss research entities - the Department of Earth Sciences of ETH Zurich, the WSL Institute for Snow and Avalanche Research SLF, located in Davos, and the Swiss company GAMMA Remote Sensing - sheds light on pros and cons of satellite radar interferometry as a tool for landslide hazard investigation. 

The scientists analysed more than a thousand Synthetic Aperture Radar (SAR) images from ESA missions to reconstruct the multi-decadal evolution of the Brienz/Brinzauls landslide complex, located in canton Graubünden, Switzerland, where a large slope failure occurred on 15 June 2023. 

The researchers used C-Band SAR datasets spanning the period 1992-2020, from ESA’s Heritage satellites ERS-1/2 and Envisat, as well as the European Union’s Copernicus Sentinel-1 mission. The study included RADARSAT data for time periods not covered by ESA missions. The results were recently presented at the General Assembly of the European Geosciences Union (EGU), and the full paper will be soon out in the scientific journal Landslides. 

The ERS heritage datasets, curated and made accessible by ESA’s Heritage Space programme – provide a long-term series of environmental data over our planet. ESA’s Envisat mission – which was operational for 10 years after its launch in 2002 – hosted an Advanced Synthetic Aperture Radar (ASAR) instrument. 

The availability of long-term datasets from these non-operational heritage missions, combined with current missions, such as Copernicus Sentinel-1, pave the way for back analyses based on Synthetic Aperture Radar Interferometry (InSAR). InSAR leverages the phase of the SAR signal, by combining two or more images over the same area to detect ground movements and their evolution over time.

The goal of the study was to reconstruct the multi-decadal spatial and temporal evolution of surface displacements at the Brienz/Brinzauls landslide complex. The researchers applied InSAR, multitemporal stacking, and Persistent Scatterer Interferometry (PSI) approaches, as used for the ESA Copernicus European Ground Motion Service (EGMS). 

“Heritage data are key to understanding the complexities of landslides and other geo-hazard processes, which might evolve over decades before having catastrophic consequences,” says Andrea Manconi, from the WSL Institute for Snow and Avalanche Research SLF, and lead author of the study.

“Compared with ERS and Envisat missions, Sentinel-1 systematic acquisitions provided better accuracies on displacements measured in Brienz. However, our analysis show that initial signs of ground deformation could be detected several years before the dramatic evolution experienced in spring 2023.” 

The study concluded that a combination of multiple remote sensing datasets is crucial for accurate hazard assessment. Furthermore, PSI results based on C-Band data alone may not be suitable to fully describe the complexities associated with large landslides scenarios, such as in Brienz. Instead, multitemporal InSAR stacking proves to be a valid approach to detect and measure spatial and temporal evolution of slope displacements.    

These results are of major relevance for understanding landslide processes, especially for those located in inaccessible regions, where remote sensing is the only viable data source to assess hazard potential and define risk scenarios.