## 5 Comparison and Discussion  
Quantitative accuracy assessment is essential for evaluating the usability and reliability of InSAR-derived deformation [49]. However, except for the one GPS station, no other ground measurements are available, and thus, an alternative approach was used to perform cross-validation among the results from the three InSAR methods.  
To compare the deformation results obtained from the D-InSAR, PS and SBAS-InSAR methods, the mean deformation velocity of D-InSAR processing results was calculated by averaging the displacement values. As explained in previous Section 4.2.1, the rate of deformation in 2003-2006 is different from that in 2006-2010, and the D-InSAR derived deformation is obtained from the data in 2007-2009. That is, the D-InSAR results are only comparable to the deformation rate in 2006-2010. Therefore, the deformation rate of PS and SBAS-InSAR in 2006-2010 are considered for further comparison. We selected 500 reference points from the PS-InSAR results in the study area, including both the stable and deformed areas (Figure 9d). The LOS displacement velocity for these  
Figure 8: (**a–d**) Comparison of time series deformation obtained by the PS-InSAR and SBAS-InSAR methods at the selected locations T1 to T4 (Figure 7).  
points was plotted compared with the SBAS and D-InSAR results, and the correlation coefficients were calculated. The results show good agreement between the SBAS and D-InSAR methods with a correlation of 0.75, and the RMSE was approximately 4.918 mm/year. However, the results from the D-InSAR and PS-InSAR were not as comparable, with a low correlation of 0.54 and an RMSE of 6.043 mm/year. However, all the three methods could identify the main deformation areas, except for one of the main deformation areas in PS-InSAR indicated in black circles in Figure 7a. This may be caused by low backscatter in the wide non-urban land use, where the sufficient number of PS points could not be detected in the PS-InSAR processing.  
Although the XJKL is the only GPS station located within the study area and is insufficient to measure and represent the entire deformation area, it provides a means of assessing the accuracy of the InSAR data and methods used in this study. The deformation rate at the XJKL continuous GPS station was 9.6 mm/year, while the D-InSAR and SBAS-InSAR derived deformation rates were 1.2 and 7.4 mm/year, respectively. No displacement was found in the PS-InSAR measurement results. In addition, the identified deformation area and the temporal evolution pattern in this study agree well with the results obtained by [PERSON] et al. [36]. In our study, the maximum deformations from 2003 to 2010 for SBAS and PS-InSAR were approximately 22.7 cm and 17.8 cm, respectively, and the results of D-InSAR was 13 cm for the period 2007 to 2009, which are comparable to the previous research results in which the maximum uplift magnitude was reported as 20 cm over the years 2006 to 2010 [36]. The comparison result shows slight differences between the two results, which might be caused by the differences in the deformation trend in the different periods, rather than any deficiencies in one method over the other. As shown in Figure 6, the deformation was evident and more accelerated from 2006 to 2010 than during the previous time of 2003 to 2006.  
Figure 9: Comparison of mean deformation velocity among D-InSAR, PS-InSAR and SBAS-InSAR methods (**a-c**) for the selected locations, shown as pink cross lines, in (**d**), showing the distribution of the selected 500 reference points. The blue triangle denotes the location of previous GPS station [36].