Research Of Space-borne Interferometric SAR Fault Zone Deformation Monitoring Based On Reconstructed Phase

With the long-term accumulation of stress,slow crustal tectonic movement occurs in seismic fracture zone,which intuitively reflects in ground deformation.The surface deformation monitoring of fault zone has instructional significance on the understanding of seismic source,earthquake cycle,seismic hazard and dynamic characteristics of seismogenic fault.Differential synthetic aperture radar interferometry(DInSAR)is a kind of new remote sensing techniques that has been developed since the late 1990s.By utilizing the phase differences between two SAR images acquired in same area with similar angle,this technique can obtain large continuous deformation fields with high accuracy.Therefore,the DInSAR technique has been widely used in all kinds of ground deformation monitoring.Due to the interference of temporal/spatial decorrelation and atmospheric phase delay,a series of multi-baseline DInSAR techniques has been developed.Traditional point-target based observation methods(e.g.precise leveling,global positioning system and so on)have high costs and are difficult to monitor land deformation from a macroscopic view,and the multi-baseline DInSAR techniques overcome these shortcomings and become one of the most promising techniques.Such techniques obtain differential interferograms with different temporal/spatial baselines by utilizing multiple SAR images,and separate the coherent targets' phase components contributed by ground deformation by taking advantage of their different spatial/temporal characteristics.The final measurements of multi-baseline DInSAR techniques are the deformation of extracted coherent targets.If the density of coherent targets is low,the macroscopic surface deformation phenomenon of the study area cannot be exhibited effectively.The main challenge of extracting the surface deformation field of fault zone by utilizing multi-baseline DInSAR techniques is that the density of monitoring measurements cannot be effectively enhanced.There are mainly two reasons causing this problem:1)the earthquake fault zones are usually untraversed and with high vegetation coverage,there is lack of coherent targets such as artificial structures.2)the magnitude of ground deformation of fault zone is relatively small,usually interferograms with relatively long temporal baseline are needed to extract effective deformation information.Therefore the decorrelation of the corresponding interferograms is inevitably high,leading to the decrease of the number of the coherent targets.The recently developed phase reconstruction technique is capable of minimizing the interferometric decorrelation noise in multi-baseline DInSAR by reforming stable phase components based on the coherence matrix estimated from each multi-look target.In this way,the number of coherent targets is essentially increased,which makes this technique one of the hottest technologies in radar interferometry.In this dissertation,the basic theory and processing strategy of multi-baseline DInSAR techniques are systematically analyzed,the fundamental reason for the restriction of increasing the density of monitoring measurements is studied,and the corresponding solutions are explored.The main research work in this dissertation is listed below:(1)The basic theory of the phase reconstruction technique is further studied.The two most commonly used phase reconstruction algorithms-phase triangulation and phase linking method-are evaluated using both simulated and real data.The experimental results demonstrate that the phase reconstruction techniques effectively enhance the data coherence in areas of moderate coherence,which lays the foundation of the increase of deformation measurements in multi-baseline DInSAR techniques.Besides,a comparative analysis of these two methods are conducted,which comes to the conclusion that both methods are of high success rate and reliability,while the computational efficiency of the phase linking method is superior to the phase triangulation method.(2)Combined with phase reconstruction techniques,traditional multi-baseline DInSAR processing strategy is improved,and a complete processing scheme aim at deformation monitoring of fault zone is designed.Due to the relatively small magnitude of deformation of fault zone,corresponding fault model is introduced in order to avoid the erroneous eliminations of the phase contributed by ground deformation during the process of estimating and eliminating phase induced by atmospheric phase screen.(3)The designed processing scheme is applied to 19 ASAR images acquired over Longmen Shan fault zone,the corresponding LOS deformation field is extracted,and the effectiveness of the designed processing scheme is verified.In order to validate the application effect of the phase reconstruction technique,the monitoring results with and without utilizing phase reconstruction technique are presented.Through comprehensive analysis,it is validated that phase reconstruction techniques are capable of effectively increasing the density of deformation measurements in seismic fault zone.