Research On Surface Deformation Of Downtown Chengdu Based On Sentinel-1A Data

In recent years,the problem of land subsidence in urban areas has attracted more attention.In addition to traditional GPS and leveling,Synthetic Aperture Radar(SAR)is also being applied for monitoring land subsidence.Microwave remote sensing is efficient,and the scattering characteristics of the target involves frequency,phase,magnitude,polarization information,and etc.Differential Interferometric Synthetic Aperture Radar(D-InSAR)is a technology for measuring ground deformation based on Synthetic Aperture Radar Interferometry(InSAR).Digital Elevation Model(DEM)can be derived from InSAR technique,which can be used to remove topographic noise for detecting subtle ground deformation.Sentinel-1A is an Earth observation satellite with central wavelength up to 0.56 cm launched by the European Space Agency(ESA)on April 2014.The study area is located in the urban areas of Chengdu,and the central location of it is 103°55'48 "E and 30°40'48" N.In this thesis,the Sentinel-1A Interferometric Wide Swath(IW)mode data is processed using the two-track D-InSAR technique to process the 33 scenes from February 12,2017 to December 21,2018.The research contents are:(1)Compare the processing effects of ascending and decending data;(2)Compare the processing effects of VV polarization and VH polarization of Sentinel-1A data;(3)Compare the results of different filter methods and unwrapping methods for the study area;(4)Analyze the effects of precipitation and earthquake on surface deformation in the study area.The major work and accomplishments for the study area are as follows:(1)The coverage of the ascending image for the study area is better than that of the decending image,and the treatment effect is also slightly better than that of the decending image;(2)The VV polarization coherence results is higher than VH polarization by comparing the effects of interference and analyze the coefficient of coherence in the interferogram.(3)The best filtering method is the last one of Adaptive,boxcar,fixed-power index Goldstein and adjusted the power index Goldstein by the coefficient of correlation from analyze noise removal and boundary fringe effects.In the uwrapping method,the Minimum Cost Flow is better than the Region Growing,because of the less disentanglement island.(4)The total surface deformation of the study area from February 12,2017 to December 21,2017 is between-10 and 10 mm,and the total deformation around it is between-30 and 30 mm.Deformation results are basically consistent with GPS measurement data and historical data;(5)That the increase in precipitation in the study area and its surroundings will cause surface upraise in the study area.Because the study area is located in the Chengdu Plain,which is high in the west and low in the east,the groundwater content decreases from west to east.Affected by the precipitation on the west side,and the impact for a long time.During the period from February 12 to December 21,2017,the surface deformation in the study area is between 0 and 40 mm,which may be caused by the increase in precipitation.(6)The surface of the study area will rise due to the increase in the number of earthquakes in the surrounding area and the increase in magnitude.This lifting effect is obvious but has a short-term effect and is weak in a long period of time.It is relatively obvious to lift the amount of precipitation during periods of low precipitation,and the effect of the increase is weaker than that of precipitation in the long period of heavy rainfall and concentration,.During the period from February 12 to December 21,2017,the surface deformation of the study area was between 0 and 30 mm,which may be due to increased earthquakes and increased magnitude.