## 5 Discussion
### General Displacement Patterns and Measurement Errors with Respect to Previous Findings  
The ground heave right after thaw has been also observed by [PERSON] et al. [10] for Sentinel-1 and has been attributed to excess snowmelt water percolating into the soil and eventually producing heave of up to 1 cm as observed in situ by [PERSON] [66].  
[PERSON] et al. [12] also show lower InSAR-derived displacements (from X-band) than in situ observation and attribute this to the shorter observation period, the temporal offset of the satellite acquisitions and undersampling of the SAR data in relationship to large local variations of the rates of movements, which can cause phase unwrapping errors. We have applied an offset correction to the C-band observation to account for the temporal offset and confirmed the approach by comparison to very dense X-band observations (starting at first day of thaw). We have applied a scaling factor to correct the line of sight observations for viewing geometry in addition. The nevertheless remaining underestimation indicates additional factors. This may include the in situ measurement technique. The plates which are used may alter the heat transfer and only represent sites which are not shaded by vegetation. The satellite retrievals also include such sites. This issue may not apply at high Arctic sites as investigated by [PERSON] et al. [12], where the offset correction might result in better agreement with the in situ measurements. Smaller values than in situ records have been also reported for L-band in comparison to frost tube measurements [20]. The year of the in situ measurements did, however, not coincide with the satellite observations. Further cases of underestimation are also known from other environments and phenomena, e.g., related to mining [67]. The rate of displacement in mid-thaw season is, however, similar between the in situ and satellite observations. This indicates an impact on the InSAR retrievals at the beginning of thaw.  
The larger subsidence in lacustrine floodplains (partially drained lakes) agrees with previous findings, (e.g., [12; 14; 68]). Our results further show that summer temperature differences between the years also have a higher impact in such areas as also over dry to moist tundra what is of relevance in the context of climate change.  
Changes in surface moisture are expected to impact the retrieval as the radar signal may penetrate deeper into the soil under dryer conditions, (e.g., [10; 11; 12]). The found apparent relationship between DDT and subsidence for the dominating landscape type indicates a limited impact on central Yamal.  
Stacking a series of Sentinel-1 12-days interferograms over one summer season in a row results in an expected displacement error on the order of 1 cm due to noise and atmospheric artifacts in the troposphere [14]. A similar error is expected for X-band data. For low-land permafrost we should however also take into account possible effects on the interferometric phase of varying ionospheric, soil moisture, snow cover, and vegetation conditions, what may limit the accuracy of the estimated deformation. In addition, on local areas undersampling of the SAR data in relationship to the large rates of movements can cause phase unwrapping errors, leading to an underestimation of the displacement.