A Study On The Mechanism Of Permafrost Surface Deformation Based On Multi-source Remote Sensing Data

The freeze-swelling and thaw-settling phenomena of permafrost can cause non-uniform deformation of the ground surface,which in turn affects the infrastructure construction stability in permafrost areas.The study on the mechanism of permafrost surface deformation can help to reveal the causes of permafrost deformation,determine the main influencing factors of permafrost surface instability,and provide technical support for the construction and maintenance of permafrost engineering projects.This thesis employs multi-source remote sensing data and selects the Norilsk region as the research area to study the permafrost surface deformation mechanism.Firstly,the Sentinel 1B data are processed by the Small Baseline Subset Interferometric Synthetic Aperture Radar technique to obtain the long-term surface deformation rate distribution.Meanwhile,the deformation results are decomposed into interannual deformation and seasonal deformation by using the sinusoidal decomposition model to study the deformation characteristics.Then Johansen model and Stefan model are used to process ERA5-land data,surface parameter data and MYD11A2 surface temperature data to extract soil thermal conductivity and interannual thawing depth of permafrost,and explore the influence mechanism of annual average temperature variation on interannual thawing of permafrost.In addition,this thesis extracts the evolution of snow and ice,water,and vegetation during summer thawing based on Sentinel 2 data,and investigates the seasonal thawing mechanism by combining temperature and soil water content data.Finally,this thesis uses a quadratic difference model to solve the topographic slope and compare it with the surface deformation rate to study the effect of the topographic slope on the surface deformation of permafrost.After research and analysis,it is found that permafrost surface deformation is the combined result of interannual deformation accumulating,summer melting and sinking,and topographic factors.A sustained rise in the annual average temperature increases the internal energy of the active layer and hinders the repeated ice segregation of unfrozen water,and then promotes the subsurface ice degradation near the permafrost table and the thickening of the active layer,which eventually leads to the deepening of interannual thawing and interannual surface subsidence.During the summer thawing process,the heat from the atmospheric system is absorbed by the active layer and transferred downward from above,the thawing front drops and the free water migrates downward under the combination of gravity and temperature gradient,causing the subsurface ice to gradually melt,thus leading to the summer thawing and sinking of the permafrost surface.And when the topographic slope is larger than 15°,the trend of the interannual sinking of permafrost and summer thawing will be intensified.Additionally,this thesis also proposes a method for monitoring the surface deformation of permafrost: employing air temperature and land surface temperature data to monitor the permafrost area,and when it is found that the annual average temperature continues to increase at a rate of 2℃/year for two consecutive years and causes a gradual deepening of the interannual thawing depth,permafrost areas with relatively large topographic slopes(greater than 15°)should be monitored by employing surface deformation monitoring techniques during the summer thaw period,and relevant measures should be taken in time for the areas with serious deformation.