Study On Ground Subsidence And Snow Depth Estimation With InSAR Technology

The exploitation and utilization of underground resources not only bring great benefits to China's economic development,but also bring lots negative impacts to the local ecological and geological environment,as well as the human environment.Timely and effective monitoring of ground surface subsidence is of great practical significance in grasping the degree of surface damage,reasonably arranging resource extraction,guiding environmental restoration,and disaster prediction.As one of the most active and widely distributed elements in the global cryosphere,snow cover plays an important role in the global water cycle.Snow depth is one of the important parameters of the snow water equivalent invers ion,its accurate inversion plays an important role in regional hydrology.The traditional ground-based monitoring methods consume a lot of manpower,material and financial resources,and in many ways cannot meet the actual needs.Therefore,Interferometric Synthetic Aperture Radar(In SAR),which has the characteristics of high temporal-spatial resolution,wide coverage,all-time and all-weather observation,has gradually become a new approach of earth observation.In the vertical deformation monitoring of the mining area,firstly,two scenes of Sentinel-1A radar images were used to acquire line-of-sight displacement by D-In SAR technology from February 17,2016 to April 5,2016 in Xuangang mine area.Then the vertical deformation was calculated by the regular and Li et al.2015 method,respectively.Through comparison,it is found that the vertical deformations calculated by the two methods have similar characteristics in spatial distribution,and there are differences only in the local settlement values.Therefore,when the law of large-scale vertical deformation monitoring is required in mining area,the monitoring accuracy of regular method can meet the actual needs.In the monitoring of ground surface subsidence in urban area of Taiyuan City,33 pairs of Sentinel-1A radar images were used to obtain subsidence law of time series by Small Baseline Subset In SAR(SBAS-In SAR)from February 18,2018 to March 3,2020.A comprehens ive analysis of the obtained annual average subsidence rate and cumulative subsidence of time series found that the main settlement areas in the last two years were Xiaodian district,north of Jinyuan d istrict and near Yangjiayu in urban area of Taiyuan City.The subsidence characteristics are related to the increase of overground buildings and structures loads and groundwater demand due to the rapid development of Taiyuan City.In the snow depth invers ion,three methods were used for snow depth invers ion in the Altay region.(1)The snow phase was acquired based on two scenes of radar images that before and after snowfall by D-In SAR,then the propagation path of radar beams in snow was used to establish the relationship between snow phase and snow depth;(2)the phase difference of multiple consecutive interference pairs was obtained by D-In SAR,combined the changes in measured snow depth,the snow phase difference and the measured snow depth change was established by the linear and nonlinear fitting method;(3)Based on the backscattered intens ity of radar images,combined with the measured snow depth to establish the relationship between the bac kscattered intensity and the measured snow depth.After comparing with the measured snow depth,it is found that the invers ion snow depth by first method is consistent with the trend of the measured snow depth,but less than the measured snow depth when there is no multiple snow cover or snow melting during two radar image acquisitions;the root mean square error of the inversion snow depth from the linear and nonlinear fitting formula is about 1.98 cm and 1.89 cm within a snowfall cycle(from winter to spring),respectively;when the snow depth within a snowfall is greater than 16 cm and less than 18.1 cm,the difference between the snow depth obtained from the backscatter intensity fitting formula and the measured snow depth is more smaller.Therefore,when the In SAR technology was used to invert snow depth,one or more of the above methods should be used to invert snow depth according to different snowfall laws in different areas.