Abstract
In permafrost areas, seasonal freeze-thaw cycles result in upward and downward movements of the ground. For some permafrost areas, long-term downward movements were reported during the last decade. We measured seasonal and multi-year ground movements in a yedoma region of the Lena River Delta, Siberia, in 2013–2017, using reference rods installed deep in the permafrost. The seasonal subsidence was 1.7 ± 1.5 cm in the cold summer of 2013 and 4.8 ± 2 cm in the warm summer of 2014. Furthermore, we measured a pronounced multi-year net subsidence of 9.3 ± 5.7 cm from spring 2013 to the end of summer 2017. Importantly, we observed a high spatial variability of subsidence of up to 6 cm across a sub-meter horizontal scale. In summer 2013, we accompanied our field measurements with Differential Synthetic Aperture Radar Interferometry (DInSAR) on repeat-pass TerraSAR-X (TSX) data from the summer of 2013 to detect summer thaw subsidence over the same study area. Interferometry was strongly affected by a fast phase coherence loss, atmospheric artifacts, and possibly the choice of reference point. A cumulative ground movement map, built from a continuous interferogram stack, did not reveal a subsidence on the upland but showed a distinct subsidence of up to 2 cm in most of the thermokarst basins. There, the spatial pattern of DInSAR-measured subsidence corresponded well with relative surface wetness identified with the near infra-red band of a high-resolution optical image. Our study suggests that (i) although X-band SAR has serious limitations for ground movement monitoring in permafrost landscapes, it can provide valuable information for specific environments like thermokarst basins, and (ii) due to the high sub-pixel spatial variability of ground movements, a validation scheme needs to be developed and implemented for future DInSAR studies in permafrost environments.
Highlights
In the Northern Hemisphere, permafrost occupies up to 18% of the land area [1], and its depth reaches up to 1500 m below the land surface in particular areas of Eastern Siberia [2]
This study contributes to the developing method of Differential Synthetic Aperture Radar Interferometry (DInSAR) estimation of ground displacements related to thawing and freezing processes in permafrost environments
We show the interferometric processing steps and intermediate results to demonstrate the general limitations of X-band DInSAR for permafrost subsidence monitoring
Summary
In the Northern Hemisphere, permafrost occupies up to 18% of the land area [1], and its depth reaches up to 1500 m below the land surface in particular areas of Eastern Siberia [2]. Cycles of freezing and thawing in the active layer result in seasonal vertical movements of the ground surface in both directions, i.e., uplift and settlement or subsidence. The magnitude of these movements largely depends on the ice/water content and its distribution in the active layer. The longer waves can be more sensitive to the soil moisture changes between SAR acquisitions due to potentially deeper penetration into the ground, causing larger errors in displacement estimations (e.g., [19]) Another potential problem for DInSAR is a non-uniform distribution of water/ice in the ground, which leads to heterogeneous uplift/subsidence within a DInSAR resolution cell. We compare the DInSAR results with the surface wetness spatial distribution estimated from the near infra-red band of a high-resolution optical image
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
