| The Tibetan Plateau is the main distribution area of permafrost in the middle and low latitedes and a climate change sensitive area,and its permafrost has undergone various degrees of degradation in the past decades.Surface deformation monitoring of permafrost in this area can help to further understand the degree of permafrost degradation in the context of global warming.Interferometric Synthetic Aperture Radar(InSAR)technology can monitor the surface deformation caused by the freezing and thawing of active layers on a regional scale.The permafrost on the Tibetan Plateau displays five different thermal stability states(Extremely stable,Stable,Semi-stable,Transitional and Unstable),representing the differences in long-term stability and susceptibility to degradation of permafrost at high altitudes in the Tibetan Plateau region.However,current InSAR-based surface deformation studies do not consider the differences and effects of permafrost thermal stability state,which makes the analysis of deformation patterns inadequate for permafrost deformation monitoring studies on a large scale.In summary,three permafrost areas with different thermal stability on the Tibetan Plateau were selected as the study areas,and the time series of surface deformation in each study area from March 2018 to February 2021 were obtained by SBAS-InSAR technique based on Sentinel-1A satellite descending SAR data,the accumulated deformation and linear deformation rates obtained were used to analyze the spatial and temporal distribution characteristics of surface deformation in different thermal stability states.Two deformation magnitude parameters,seasonal deformation amplitude and annual deformation rate,were fitted by the periodic deformation model to quantify and analyze the magnitude and characteristics of surface deformation in permafrost areas with different thermal stability.The main findings are as follows.(1)The overall deformation in the study area of Yeniugou,which is mainly Unstable and Transitional type permafrost,is relatively stable in the past three years.The seasonal deformation amplitude is mostly within 9.5 mm,with a mean value of3.3 mm,and the interannual deformation rate is mainly concentrated in-15.1?15mm/yr,with a mean value of-0.1 mm/yr.The area where subsidence occurs is mainly concentrated in the Unstable type permafrost area on both sides of the upper reaches of Yeniugou River.The subsidence area is characterized by a clear cyclic pattern.The seasonal deformation amplitude varies significantly with the slope angle,and the seasonal deformation rate is the largest on the north slope.The correlation between the interannual deformation rate and the ground ice content and the mean annual temperature is not obvious,and the seasonal amplitude and interannual rate in this study area are to some extent mutual controlling factors.(2)The Qumar River study area,which is dominated by Transitional and Semi-stable type permafrost,has an obvious subsidence trend in the past three years and experiences a very obvious cyclical freeze-thaw cycle with seasonal changes.The seasonal deformation amplitude is mostly within 25.8 mm,with a mean value of 12.9mm,and the interannual deformation rate is mainly concentrated in the range of-17.6to 5.5 mm/yr,with a mean value of-6.1 mm/yr.The area with large amount of subsidence is mainly distributed in the mountainous area north of Zonag Lake to the south of Kunlun Mountain Range,and the area north of Zonag Lake to the east of Yuexibagou,the mountain slope north of the Cuodarima Lake and Duoergaicuo Lake and the Fenghuoshan.There exists a situation where the Semi-stable type has a greater rate of surface subsidence than the Transitional permafrost.The seasonal deformation amplitude varies significantly with the slope angle,and the seasonal deformation of the northern slope is the largest.The higher ground ice content or the lower the mean annual ground temperature,the greater the subsidence rate.When the seasonal amplitude is less than 20 mm,it can be used as one of the control factors for the interannual deformation rate.(3)The overall linear deformation trend in the study area of Golmud,which is dominated by Semi-stable and Stable type permafrost,is obvious in the last three years.The seasonal deformation amplitude is mostly within 8 mm,with a mean value of 3.7 mm,and the interannual deformation rate is mainly concentrated in the range of-23 to 10 mm/yr,with a mean value of-6.5 mm/yr.The areas with higher subsidence are mainly located in the Stable and Semi-stable type permafrost areas in the foothills of Kunlun Mountains and the Transitional and Unstable type permafrost areas in the northeast corner,and there is a situation that the Stable type has a faster subsidence rate than the Unstable type permafrost area.The seasonal deformation amplitude significantly with the slope angle,and the seasonal deformation variable is the largest on the north and south slopes.Both the seasonal amplitude and interannual rate are not mutually controlling factors in this study area.(4)The cumulative deformation of the surface in the study area of Yeniugou,where the overall thermal stability is poor,is not large.The main subsidence area belongs to the Unstable type permafrost,and the magnitude of seasonal deformation in the subsidence area is large.However,the subsidence trend in the study areas of Qumar River and Golmud,which have an overall better thermal stability,is obvious.The former is dominated by cyclic deformation,while the latter is dominated by linear deformation.Ground ice content and annual mean ground temperature are the main environmental factors affecting the magnitude of interannual deformation rate.In addition,slope angle has a greater influence on the amplitude of seasonal deformation in the three study areas,followed by NDVI and soil bulk density. |
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