The key challenge of PSInSAR(Permanent Scatter Interferometric Synthetic Aperture Radar)lies in the quality of Permanent Scatter(PS)points, which are difficult to extract accurately in fracture zones due to the complex natural ground cover and unique geomorphological environments. In such areas, the inability to reliably extract high-quality PS points limits the application of PSInSAR for monitoring interseismic deformation. To address the problem of high-quality PS point selection in fault zones and improve the effectiveness of PSInSAR technology for monitoring interseismic deformation, this paper presents a comparative study of coherence coefficient and amplitude deviation double thresholds. The study further integrates the Kolmogorov-Smirnov(KS)test and CR homogeneous pixel method, in addition to conventional coherence coefficient point selection techniques. Sentinel-1A SAR images from March 14, 2015, to February 16, 2020, are used as the data source, with the Wushan-Gangu section of the fault zone on the northern edge of the Western Qinling Mountains, near the northeastern edge of the Qinghai-Tibet Plateau, serving as the test area for PSInSAR processing. The quality and reliability of PS point selection using various methods are compared and analyzed.

Two sets of coherence coefficient T_γ and amplitude deviation D_γ double thresholds were tested. The coherence coefficient was set at T_γ=0.5, while the amplitude deviation D_γ was set to 0.5 and 0.3, resulting in 19806 and 2485 PS points, respectively. When the amplitude deviation threshold was lowered, the number of PS points on ridgelines decreased significantly, while there was little change in Gangu County, suggesting poor pixel amplitude stability in mountainous areas. Lowering the threshold eliminated many PS points, retaining only those with high amplitude and stable time series, typically found in hard targets like urban buildings. A KS double sample test was then applied in combination with the double threshold method, with all thresholds coefficient T_γ, amplitude deviation D_γ, and KS test P_γ set at 0.5. This approach yielded 1 313 PS points, showing a significant reduction in PS points on ridgelines and in Gangu County, while urban points became more concentrated on hard targets like buildings. Although the KS test reduced PS points in vegetated areas, it did not fully eliminate noise points. Finally, based on the double threshold results of coherence coefficient T_γ=0.5 and amplitude deviation D_γ=0.3, both the KS test and CR homogeneous pixel selection methods were applied. The CR homogeneous pixel method used a phase difference threshold P_γ=0.5 and a temporal phase stability threshold N_γ=50. This yielded 2 485 PS points for the double threshold method, 133 PS points for the double threshold plus KS test, and 414 PS points for the double threshold plus CR homogeneous pixel method. The latter two methods significantly reduced PS points, with a higher concentration of points in Gangu County, consistent with the expectation that PS points predominantly correspond to hard targets like buildings.

Statistical analysis of the results demonstrated that the combination of the coherence coefficient, amplitude deviation, and CR homogeneous pixel method provided the highest quality PS points, effectively excluding noise points in vegetated areas. The combination of coherence coefficient, amplitude deviation, and KS test ranked second, improving accuracy in urban areas but failing to eliminate noise in vegetated areas. Using Sentinel-1A SAR images and the Wushan-Gangu fault as the test area for time series PSInSAR processing, the accuracy of PS point selection was further verified. A comparative analysis of deformation monitoring results from the three methods revealed that both the KS test and CR homogeneous pixel method improved the accuracy of fault deformation monitoring, with the CR homogeneous pixel method yielding superior results. Monitoring data from 2015 to 2020 showed that the deformation rate of the northern block of the Wushan-Gangu fault ranged from -2 to -0.2mm/a, with an average deformation of approximately -1.7mm/a. In contrast, the southern block exhibited a deformation rate between 0.3 and 0.5mm/a, with an average deformation of about 1.8mm/a The relative average deformation rate between the northern and southern blocks was 0.7mm/a, indicating left-lateral strike-slip movement. Among the three methods, the double threshold plus CR homogeneous pixel method produced PS points with the smallest deformation rate standard deviation, indicating more stable and reliable deformation results.

This study focuses on four moderate-sized earthquakes in the northern margin of the Qaidam Basin, northeastern Tibet Plateau, China, of which one occurred in 2008, and three in 2009, respectively. We obtain coseismic displacement fields of these four events using Envisat descending ASAR data and D-InSAR technology. The results show that the 2008 earthquake has only one deformation center and the 2009 earthquakes have three deformation centers in their fields. The maximum displacement of 2008 and 2009 earthquakes are 0.097m and 0.41m in the LOS(line of sight), respectively. We invert ground displacements of these earthquakes based on elastic dislocation models to estimate slip distribution on fault planes. For the 2008 event, using a one-segment fault model, the inversion reveals peak slip of about 0.47m occurring at a depth of 19km. For the 2009 earthquakes, the ground displacement pattern observed by InSAR can be fitted by a three-segment fault model with smallest RMS of residuals. The three sectional fault model is considered the most reliable.

We achieved the coseismic displacements of the Napa M_W6.1 earthquake located in California US occurring on 24 August 2014 by using InSAR data from the newly launched ESA's Sentinel-1A satellite. The 30m×30m ASTER GDEM was used to remove the terrain effect, and phase unwrapping method of branch-cut algorithm was adopted. In order to obtain a better coseismic displacement field, we also tested 90m×90m SRTM data to remove the terrain effect and Minimum Cost Flow algorithm to unwrap the phase. Results showed that the earthquake caused a significant ground displacement with maximum uplift and subsidence of 0.1m and -0.09m in the satellite light of sight(LOS). Based on the Sentinel-1A dataset and sensitivity based iterative fitting(SBIF) method of restrictive least-squares algorithm, we obtained coseismic fault slip distribution and part of the earthquake source parameters. Inversion results show that the strike angle is 341.3°, the dip angle is 80°, rupture is given right-lateral fault, average rake angle is -176.38°, and the maximum slip is ~0.8m at a depth of 4.43km. The accumulative seismic moment is up to 1.6×10¹⁸N·m, equivalent to a magnitude of M_W6.14.

In the past few years, the improved InSAR technology based on time series analyses to many SAR images has been used for measurement of interseismic deformation along active fault. In the paper, we first made a summary and introduction to the basic principle and technical characteristics of existing Time Series InSAR methods(such as Stacking, PSInSAR, SBAS). Then we presented a case study on the central segment of Haiyuan Fault in west China. We attempt to use the PS-InSAR(Permanent Scatter InSAR)technique to estimate the motion rate fields of this fault. We processed and analyzed 17 scenes of ENVISAT/ASAR images in descending orbits from 2003-2010 using the PS-InSAR method. The results reveal the whole movement pattern around the Haiyuan Fault and a remarkable velocity gradient of about 5mm/a across the central segment of the fault. The motion scenes are consistent with left-lateral strike-slip. On this basis, we make a discussion on some issues about observation of fault activity using Time Series InSAR methods, such as the changes of LOS deformation rates with fault strike and region width observed across a fault, fault reciprocity and motion style indicated by Time Series InSAR rate map and the relationship between the InSAR LOS deformation and the ones from other methods. All these studies will benefit the promotion of InSAR application in detection of tectonic movement.

Vertical coseisimic deformation near seismogenic fault is one of the most important parameters for understanding the fault behavior, especially for thrust or normal fault, since near field vertical deformation provides meaningful information for understanding the rupture characteristics of the seismogenic fault and focal mechanism. Taking Wenchuan thrust earthquake for an example, we interpolate GPS horizontal observed deformation using Biharmonic spline interpolation and derive them into east-westward or north-southward deformation field. We first use reliable GPS observed value to correct InSAR reference point and unify both GPS and InSAR coordinate frame. We then make a profile using InSAR data and compare it to that from GPS data and we find GPS and InSAR observation reference point has a 9.93cm difference in the hanging wall side, and around -11.49cm in the footwall. After correction, we obtain a continuous vertical deformation field of the Wenchuan earthquake by combined calculation of GPS and InSAR LOS deformation field. The results show that the vertical deformation of both hanging wall and foot wall of the fault decreases rapidly, with deformation greater than 30cm within 50km across the fault zone. The uneven distribution of the vertical deformation has some peak values at near fault, mainly distributed at the southern section(the town of Yingxiu), the middle(Beichuan)and the northern end(Qingchuan)of the seismogenic fault. These three segments have their own characteristics. The southern section of the fault has an obvious asymmetric feature, which exhibits dramatic uplift reaching 550cm on the hanging wall, with the maximum uplift area located in Yingxiu town to Lianshanping. The middle section shows a strong anti-symmetric feature, with one side uplifting and the other subsiding. The largest uplifting of the southern segment reaches around 255cm, located at the east of Chaping, and the largest subsiding is in Yongqing, reaching around -215cm. The vertical deformation of the northern section is relatively small and distributed symmetrically mainly in the north of Qingchuan, with the maximum uplift to be 120cm, locating in the northernmost of the seismogenic fault.

Differential Synthetic Aperture Radar Interferometry (D-InSAR) is a newly developed technique for monitoring large-scale ground deformation with some prominent advantages such as high accuracy and pantoscopic view. The vertical crustal deformation accuracy can be measured by D-InSAR technology to the millimeter level, but due to restrictions of spatial, temporal decorrelation and atmospheric delay, the application to the monitoring of the crust long-term slow deformation is limited. The Permanent Scatterers approach, which is based on conventional InSAR technique, puts emphasis on processing time series of SAR interferograms by recognizing and analyzing single scatterers with a stable backscatter intensity or reliable phase behavior in time, to study the deformation histories of the earth's surface in a long time series. The PS approach can better conquer problems of temporal and spatial decorrelation, also the atmospheric delay effect, which will improve the efficiency of datum utilization when measuring large time scale deformation events. The PS-InSAR, as an innovation of D-InSAR technology, can overcome the loss of coherence time, and meanwhile, calculate and eliminate the atmospheric effects to ensure the normal operation of the interferometric processing. It acquires the accumulated deformation and its rates at the coherent points in the images.
In this paper, the basic principle, advantage and status of PS-InSAR are introduced. The slight deformation of Gangu area in the fault zone along the north fringe of west Qinling Mountains which is one of the major left-lateral strike-slip active faults in northeastern margin of Tibetan plateau is monitored by PS-InSAR technology using 14 scenes of ENVISAT ASAR data from May 2008 to September 2010. The result shows that the rate of the north wall of the fault zone is -1～-2mm/a, the rate of the south wall of the fault is 3～4mm/a, and relative slip rate between the two walls of the fault zone in Gangu area along the north fringe of west Qinling Mountains is approximately 5mm/a; the points target deformation rate and deformation direction both match with the left-lateral motion feature of the north fringe fault zone of west Qinling Mountains, and results have a good agreement with the study results by other scholars. This suggests that the PS-InSAR technology is capable of detecting crustal small deformation.