| Facing with global warming,the qinghai-tibet plateau underground ice melting,frozen layer thinning and active layer thickness increase of permafrost degradation problem is becoming more and more serious,active layer of the dynamic changes of the freezing process also made the permafrost produce seasonal subsidence and uplift,the resulting construction engineering disasters and natural disasters is also rising,profoundly influenced the cold and the ecological environment,economic construction,engineering construction,etc.Therefore,it is of great practical significance to carry out long-term monitoring of surface deformation in permafrost regions for the study of the law of earth change,the protection of frozen soil environment and the safe operation of major projects.InSAR(Interferometric Synthertic Aperture Radar)technology has been gradually applied to monitoring permafrost deformation due to its high measurement accuracy,all-weather,all-day and high coverage characteristics.However,the single-orbit InSAR technology can only obtain the deformation characteristics of the line of sight(LOS),so it is unable to grasp the real deformation law of permafrost more comprehensively.So in this paper,the Beiluhe as the research area of permafrost along the qinghai-tibet railway,based on ascending and descending InSAR results,combined with the geometric parameters of radar information,Obtained the real two-dimensional surface time series deformation results of permafrost from 2015 to2020.Based on this analysis,the real two-dimensional deformation temporal and spatial distribution characteristics of permafrost were analyzed,the active layer thickness of the study area was inverted,and study the relationship between different environmental factors and the real two-dimensional deformation of permafrost.The main research results and conclusions are as follows:(1)The spatial and temporal distribution characteristics of surface deformation in the study area are different in east-west direction and vertical direction,and the main deformation is vertical subsidence,but the deformation ability in east-west direction is weak.In general,the vertical deformation presents an obvious spatial distribution pattern of slope erosion and subsidence on both sides of the gully and accumulation and uplift in the gully.On the basis of the linear uplift or subsidence trend,the deformation of time series shows obvious periodic change characteristics,and the average cumulative shape variable of subsidence and uplift region from 2015 to 2020 is 57 mm and 24 mm,respectively.The east-west deformation presents a spatial pattern along slope direction.The cumulative deformation of time series mainly shows a linear increasing trend,but has a certain fluctuation.The average cumulative deformation shape variable in the east-west deformation region from 2015 to 2020 is less than 25 mm.(2)The spatial distribution of annual vertical deformation and seasonal deformation variables of permafrost is related to surface type and topography,and the spatial distribution of east-west annual deformation is mainly affected by topography,but the dominant factor affecting the spatial distribution of permafrost deformation is soil moisture content.In the flat region,the annual and seasonal vertical deformation rates of vertical and horizontal deformation are larger,and decrease with the increase of elevation and slope.The difference of hydrothermal conditions leads to the obvious difference of permafrost deformation in different slope directions.The east-west deformation and vertical seasonal deformation of the shady slope are both greater than that of the sunny slope.The vertical deformation and seasonal deformation in the alpine meadow area are greater than that in the alpine desert area,but the east-west deformation has no obvious change.(3)The response of surface deformation to climate in permafrost region is significant.The vertical periodic deformation is consistent with the temperature curve change,but the extreme points of frost heaving and thawing are all later than the corresponding time of 0? temperature,indicating that the surface deformation in the permafrost region is affected by temperature,but with a certain lag.The response of frost heaving and thawing in alpine meadow to air temperature is later than that in alpine desert area because of the regulating mechanism of vegetation to the internal environment of the surface.After heavy or continuous rainfall,the surface subsidence is obvious,which proves that rainfall can promote the surface subsidence in permafrost regions.(4)Due to the influence of permafrost on the Qinghai-Tibet Highway and Railway,the real two-dimensional surface deformation features of winter freezing and summer thawing are obvious.The vertical deformation of the railway and highway buffer zones in the study area is mainly subsidence,and the east-west deformation presents extrusion deformation from the middle to the two sides.The farther the distance between the two sides of the railway,the smaller the shape variable.The vertical time series deformation on both sides of the railway is mainly characterized by the seasonal characteristics of frost heaving,summer thawing and long-term subsidence trend,which may be affected by the traffic operation,and the subsidence period can last until December.The east-west time series deformation shows the characteristics of moving away from the railway track in summer thawing period and close to the railway track in winter frost heaving period.(5)Existing research results and field investigation have verified the reliability of the annual average thickness of active layer in 2017 and 2018.However,there is a significant underestimation of the thickness of active layer in the alpine meadow and the alpine desert.The thickness of active layer in the alpine meadow is about 1.5m,and the thickness of active layer in the alpine desert is between 1.5m and 3m,with great fluctuation. |
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