Multi-Geometry Sentinel-1 InSAR for Characterizing Ground Deformation in Norway

Norway is susceptible to large rock avalanches due to its mountains, long fjords, and steep valley sides. In November 2018, the Geological Survey of Norway (NGU) launched a national public service named "InSAR-Norway Ground Motion Service" (insar.ngu.no), based on Sentinel-1 Persistent Scatterer Interferometry (PSI). The service provides access to InSAR ground deformation measurements for the mainland of Norway. The service is based on the EU Copernicus Sentinel-1 satellites, providing nationwide coverage every 6 days.

The InSAR-Norway operational service has been a game changer for rockslide mapping on a nationwide scale. In order to cover all areas, we are using data from a number of satellite geometries, both from ascending and descending orbits. In addition, there is a lot of overlap between different tracks due to the polar orbits and Norway's high latitude. In effect, every point of Norway's mainland is covered by at least 4 different InSAR line-of-sight (LOS) observation geometries. However, all this information comes at a cost of increased complexity for interpretation and analysis.

InSAR-detected surface displacements in mountainous areas can be caused by various processes corresponding to different hazard levels. In order to improve hazard and risk assessment, we need to discriminate rockslides to other unstable areas such as scree deposits, rock glaciers or solifluction. Each process has specific kinematics that we can contribute to document by taking benefit of multi-geometry Sentinel-1 data.

In this work, we present a regional study in the counties of Troms and Finnmark in northern Norway, where numerous unstable rock slopes and periglacial features are present. We are combining Sentinel-1 InSAR data from different geometries, in order to estimate 2D displacements (in the E-W plane or projected along the slope). Field investigation and comparison with in-situ measurements allow for interpretation and validation of the results. The study contributes to better characterize the kinematics of unstable areas and identify specific magnitudes and orientations of displacements depending on the different behaviour of periglacial landforms.