Study On Surface Deformation Monitoring In Mining Area And Atmospheric Delay Correction Of InSAR

As an important basic energy source in China,coal resources have a beneficial impact on the economic development and social progress.However,the large-scale mining of coal is invitation to ecological environmental disasters and causes surface deformation.It is of great significance to acquire the subsidence information timely and master the changes of surface displacement for the rational and effective mining of coal resources,mine disasters warning and the protection of ecological environment.The conventional monitoring methods have some drawbacks such as high cost,large workload,low observation efficiency,low point density,and long time-consuming,which make them difficult to adapt to large-scale deformation monitoring task in the mining area.InSAR(Interferometry Synthetic Aperture Radar)technology has developed into an important method for observing ground deformation,because of its advantages of high spatial resolution,strong penetration,large monitoring range,allweather,all-day,continuous space coverage and high security.However,the issues of complex geographical environment,large deformation gradient,fast rate and lush vegetation in mining area are still the barrier of the application of InSAR technology.Therefore,in view of the shortcomings of InSAR application in mining areas,this paper took the Yuxian Coal Mine in Hebei Province as the research area to explore the monitoring methods of the ground surface subsidence with large gradient and multidimension.On the other hand,the existence of atmospheric water vapor makes the radar signal propagation path warp and the speed slow down,resulting in an additional delay through the interference phase,which causes monitoring errors to the decimeter level and decays the performance of deformation monitoring in terms of the reliability and accuracy.In this regard,this dissertation proposed an ensemble method with multiple models to reduce the error from atmosphere and took Hong Kong as the research area.The main contents of this paper are as follows:(1)The theoretical principle and research development status of InSAR were introduced.The principle and technical process of InSAR,D-InSAR(Differential Interferometry Synthetic Aperture Radar),PS-InSAR(Persistent Scatterer Interferometric Synthetic Aperture Radar),SBAS-InSAR(Small Baseline Subset Interferometric Synthetic Aperture Radar)and offset tracking were presented,respectively,and the delay effect of atmosphere was analyzed.Seven TerraSAR-X images were chosen to monitor the surface subsidence in Yuxian Coal Mine,Hebei Province based on D-InSAR technology.Monitoring results showed that several obvious subsidence funnels appear in the mining area due to the large-scale coal mining.The maximum settlement amount reached 382.86 mm,the average settlement rate was about 5.07 mm/y.Moreover,the leveling data of the nearest neighbour were used to verify the D-InSAR monitoring results,which confirmed the effectiveness of D-InSAR for deformation monitoring in the mining area.20 TerraSAR-X images were selected to obtain the deformation information in Yu County using PS-InSAR and SBAS-InSAR.Results showed that there was significant subsidence in the center area in Yu County,while slight rise in the southern area.A high consistency and correlation was presented between the two methods results,which demostrated the validity of MT-InSAR(MultiTemporal InSAR)in urban area deformation monitoring.(2)19 TerraSAR-X and 16 Sentinel-1 images were used to obtain the subsidence information in the radar line of sight of the Yuxian Coal Mine based on SBAS-InSAR,and two-dimensional deformation rates in the vertical direction and the east-west direction were captured by combining decreasing TerraSAR-X and ascending Sentinel-1 images.Considering the advantage of high precision of SBAS-InSAR in small-scale deformation and the great potential of offset tracking technology in field of large-scale deformation,this dissertation proposed a method combining SBAS-InSAR and offset tracking technology to monitor large gradient deformation based on spatial coherence map,the precision leveling data was used to verify the fusion results.The average error was about 59.3 mml between fusion resuls and leveling data,which indicates that the intergration of phase information and intensity information of SAR images could detect more reliable deformation information in large scale deformation regions.(3)In view of the influence of atmospheric delay erros in InSAR process,Power law,ERA-Interim,MERRA,GACOS and WRF were carried out respectively to estimate the atmospheric delay phase of InSAR in Hong Kong.Correction results of each method were compared and analyzed in terms of reliability and accuracy.Aiming at the defects of a single method or a single model in atmospheric correction,this work tried to estimate the atmospheric delay error by ensembling multiple methods.The comparative analysis with the results from one method alone proves the feasibility of InSAR atmospheric delay correction by combining multiple methods.