Monitoring an Arctic cultural heritage site with state-of-the-art remote sensing techniques Lessons from the THETIDA project

The Svalbard archipelago lies 1100 km south of the North Pole and 800 km north of the Norwegian coast. The region is one of the most important and strategic terrestrial nodes on Earth, separating the Greenland Sea, the Barents Sea, and the Arctic Ocean. The cultural landscape reflects human life and activity in a harsh and fragile environment.We present here the preliminary results of the pilot site from the Thetida project the coal cableway station at Hiorthhamn, 1917 (Taubanestasjonen i Hiorthhamn). The study area was extended to the town of Longyearbyen, located across the bay from Hiorthhamn. Longyearbyen is the settlement with the largest number of Svalbard residents (approximately 2500) and with an impressive number of protected cultural heritage sites approximately 400. The total number of protected cultural heritage sites in Svalbard is 4590.Previous studies have shown that the main risks to the Hiorthhamn site are coastal erosion, permafrost degradation, rockfall, thaw slumps, snow avalanches, surface erosion and thermo-erosion gullies, weathering, river flooding, and solifluction. Previous data (NPI orthophotos from 1936, 2009 2011, field surveys with UAV and total station in 2019 and 2020) and the most recent remote sensing data (Planet Sky Sat images 2023) are used to assess the risk of degradation. Coastal erosion, calculated with the help of DSAS, for the sector where the site is located, shows high erosion rates of 0.77 m/yr (for the period 1927-2020) when compared to other studies from Svalbard. The latest forecast analysis estimates that the entire area will be eroded over the next two decades.Furthermore, previous studies have shown that InSAR-based time series of land deformation appears to show continuous subsidence over permafrost regions in recent years. In this study, a method based on persistent scattering interferometry was used to estimate land deformation in the wide area of Longyearbyen, Svalbard. The InSAR-based land deformation estimates were calculated by processing 268 Sentinel-1 images from early 2018 to late 2023. Within the city of Longyearbyen, regions of stable, uplifting, and subsiding ground motion were identified. The land deformation results were interpreted by considering in-situ permafrost data and building characteristics, such as roof material, age, and heating mechanisms under building foundations. The results are important for better understanding the dynamics of the permafrost landscape under a warming climate and for predicting flooding using SAR altimetry data. The study makes a significant contribution to the protection of cultural heritage. The coal cableway station is the most iconic and visible object in Hiorthhamn, so much so that it can be seen from Longyearbyen, encouraging tourists to take a boat or a kayak to visit. Longyearbyen is the main tourist attraction on the island. It is therefore important to assess and monitor the risk of degradation so that, together with the local authorities, the most sustainable and climate-friendly measures can be taken for future generations.Acknowledgment:This research has been funded by European Unions Horizon Europe research and innovation funding under Grant Agreement No: 101095253, THETIDA project.