FrostInSAR: Upscaling the investigation of periglacial landforms in the Norwegian Arctic using Synthetic Aperture Radar Interferometry

In polar and mountainous regions, the cold climate leads to temperature fluctuations around 0 °C. The ground freezes and thaws, which causes heave and subsidence of the ground surface due to the transition between water and ice. In inclined terrain, rocks and sediments tend to move downslope under the effect of the gravity. These processes impact the ground stability, which can pose a hazard for population and infrastructure. Climatic, geologic and topographic factors control the spatial distribution and temporal behaviour of processes driven by frost and gravity, which determine the characteristics of the ground dynamics. However, the interactions between the environmental variables and the ground properties are complex and challenging to study. The availability of extensive and frequent satellite imagery provides a valuable tool to enlarge the investigation in hard-to-access polar and mountainous regions. FrostInSAR project takes advantage of the open access images acquired by the Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) satellites to analyse selected study areas in Northern Norway and Svalbard. The SAR Interferometry (InSAR) technique allows for measuring surface displacements at centimetre to millimetre accuracy, by comparing images taken at different times. The analysed changes are compared with other datasets, such as temperature measurements and field-based maps. Between 2017 and 2021, the Ph.D. candidate Line Rouyet developed InSAR displacement maps and time series and related the results to environmental variables to understand the spatio-temporal factors controlling the ground dynamics in areas with seasonal or perennial frozen ground (permafrost). The Ph.D. project focused on study areas in Troms and Finnmark (Northern Norway) and on Spitsbergen (Svalbard). FrostInSAR results show that InSAR is able to document moving landforms characterised by displacement rates ranging from millimetre to metre during a season or a year. InSAR also contributes to investigate the processes causing ground movement, as well as their relations with environmental factors, such as the temperature and the ground composition. The Ph.D. thesis highlights the potential for future exploitation of InSAR technology to improve our understanding of the processes shaping cold climate landscapes, for identifying hazardous landforms at large scale and monitoring the evolution of arctic environments affected by climate change.

FrostInSAR demonstrated the ability of InSAR to document the kinematic properties of the periglacial ground dynamics, both related to the ground freeze-thaw cycles in permafrost lowlands and the gradual downslope creeping landforms in mountainous environments. The research suggests novel ways to develop dedicated InSAR products relevant for the assessment of geohazards and the systematic observation of ground dynamics in the context of climate change. Future research in this scope is expected these coming years, especially within the framework of the Norwegian and European Ground Motion Mapping Services, the Svalbard Integrated Arctic Observing System (SIOS) and the European Space Agency Climate Change Initiative (CCI) Permafrost.

In perennial frozen ground (permafrost), the upper layer (active layer) is subject to seasonal freeze/thaw. This induces ground heave/subsidence that can affect the stability of infrastructure and slopes. In a context of climate change, the Nordic Arctic is affected by warming and permafrost degradation and is a key region in research in periglacial environments. FrostInSAR is a Ph.D. project that aims to study the potential of satellite remote sensing to upscale traditional point-scale measurements in periglacial landscape dynamics in the Arctic. By combining ground deformation derived from Synthetic Aperture Radar Interferometry (InSAR) with field observations and in-situ measurements, the project aims to measure, explain and predict the state and evolution of ground deformation related to freeze/thaw processes. This will contribute to enable adapted responses from stakeholders to deal with infrastructure and slope instability and to face the potential consequences of climate change. The Ph.D. research includes the implementation of signal processing algorithms to suit new SAR data and applications, and the development of explanatory and predictive models relating InSAR deformation to environmental variables. Sentinel-1a/b will provide valuable data to overcome some limitations of the technology related to phase ambiguity and coherence loss thanks to its short repeat pass and frequency. In addition, Radarsat-2 and TerraSAR-X data will contribute to get better spatial resolution. The project is designed to include study sites in Northern Norway and Svalbard in areas with perennial frozen ground (permafrost) or seasonally frozen ground. The project includes partners from Norut, the University Centre in Svalbard (UNIS), The Arctic University of Norway (UiT), The University of Oulu (UOulu), the ESA GlobPermafrost project via the coordinating partner ZAMG, the Austrian Zentralanstalt für Meteorologie und Geodynamik and The Chinese University of Hong Kong (CUHK).