Description: In permafrost areas, seasonal freeze-thaw cycles of active layer result in upward and downward movements of the ground. Additionally, relatively uniform thawing of the ice-rich layer at the permafrost table can contribute to net long-term surface lowering. We use a simple method to quantify surface lowering (subsidence) and uplift in a yedoma area of the Lena River Delta, Siberian Arctic (Kurungnakh Island), using reference rods (metal pipes and fiberglass rods) installed deeply in permafrost. The metal pipes were 2 m long and 3 cm in diameter and were anchored at least 1 m below the typical active layer. The fiberglass rods were 2 m long and 1 cm in diameter and were anchored at least 70 m below the typical active layer. We assume, therefore, that the rods were motionless relative to the permafrost. The plexiglass plate with a size of 10 by 10 cm was fixed in its horizontal position by the rod but could move freely with the surface vertically along the rod. We repeatedly measured distance between the top of a rod and a plexiglass plate resting on the ground surface. Several distance measurements around each rod were taken at each visit and averaged. Altogether 12 metal pipes were installed at the study site in April 2013 and 19 fiberglass rods were installed in April 2014. Measurements were conducted during field campaigns from spring 2013 to summer 2017 with some gaps. We provide here the measured distances between the top of a rod and a plexiglass plate. To obtain the ground displacement, the user have to define the period of interest and calculate the displacement.

Description: 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.

Description: Time series of TerraSAR-X backscatter intensity and 11-day interferometric coherence with high temporal resolution have been used to interpret major seasonal land surface changes in a variety of tundra environments, namely an area of wet polygonal tundra, a drier Ice Complex upland area, a recently drained well-vegetated lake basin, a partly well-vegetated floodplain, a bare sandbank, and a very dry area of rocky outcrops. Seasonal variations in intensity and coherence were evaluated in the context of meteorological conditions such as air temperatures, precipitation and snow cover status. The TSX signal appeared to have very limited penetration through vegetation and the observed variations in backscatter and coherence were therefore mainly attributed to processes in the upper layer of vegetation. Variations in the TSX backscatter intensities were mostly moderate throughout the annual cycle. Backscatter was found to be insensitive to ground freezing and thawing as well as being generally insensitive to precipitation, but it was sensitive to (i) an individual rain event at the time of SAR acquisition, (ii) an individual snow shower coinciding with unusually high air temperature, and (iii) the spring melt of the snowpack (likely with a refrozen icy crust on the surface). Flooding of the sandbank was clearly detectable from extremely low backscatter values. The selected regions of interest (ROIs) demonstrated generally good separability on the basis of differences in their backscatter intensities: rough and very sparsely vegetated rocky outcrops yielded the highest backscatter and the smooth barren sandbank yielded the lowest backscatter. The backscatter from the vegetated ROIs yielding intermediate values, with the less vegetated ROIs returning lower backscatter. Interferometric coherence comprises both amplitude and phase signal components and should therefore be more sensitive to surface changes than backscatter intensity alone, especially at the X-band frequency, an assumption that is strongly supported by the results of our investigations. The coherence decreased dramatically with the onset of snow cover in all of the landscape types. The snow melt period was also clearly identified by another reduction in coherence. The snow shower that affected the backscatter also caused a reduction in coherence. January and February yielded the highest coherence values for all of the ROIs (with mean values of up to 0.9 for the rocky outcrops).