## 4 Results and Discussion
### G1501 Highway  
During our data processing for the G1501 Highway area, unexpected orbital errors appeared in most interferograms. As shown in Figure 12, the original generated deformation map is obviously disturbed with orbital signal (the fringes ranging from green to red color in Figure 12b). The second-order polynomial fitting method is used here to remove the orbital error. As shown in Figure 12c, after simulating and deleting the linear orbital error component, the deformation signal has been extracted, with several obvious subsiding areas [44]. Figure 11: The magnitude distribution of settlement points in Lungui Road from 27 October 2014 to 27 November 2015 (\(x\) axis defines each deformation interval; \(y\) axis defines the proportion of total high coherence points). Figure 12: (**a**) The amplitude map over G1501 Highway; (**b**) The deformation map with obvious orbital error (27 October 2014 to 26 June 2015); (**c**) Corrected deformation map without orbital error (27 October 2014 to 26 June 2015). Figure 13 shows the average linear velocities comparison for two models over G1051 Highway. As shown in Figure 13, the linear model and seasonal model demonstrate good agreement in spatial distribution, with the deformation velocity generally ranging from \(-27\) to \(-8\) mm/yr and the color ranging from light green to orange yellow. The large subsidence points are mainly concentrated in the upper left and bottom right part of the images, with the maximum velocity up to \(-63\) mm/yr detected from linear model and \(-57\) mm/yr from seasonal model. Figure 14: Time series deformation of G1501 Highway based on the linear model (referenced to 27 October 2014). Figure 13: The average velocity maps over G1501 Highway generated by two models. (**a**) Linear model result; (**b**) Seasonal model result. The time series deformation results of G1051 area obtained by the linear model and seasonal model are shown in Figures 14 and 15, respectively. From Figure 14, no obvious discipline of the temporal deformation variation can be found, and the temporal evolution over this stretch of highway performed relatively smoothly. From January 2015 to August 2015, the subsidence is slightly increasing, whereas from August 2015 to November 2015, the subsidence showed a slowly decreasing fluctuation, with the maximum cumulative deformation of \(-65\)mm in August 2015. In contrast, the results generated by the seasonal model showed a more obvious periodic fluctuation. The subsidence gradually increased from December 2014 to June 2015, with the peak value of \(-67\) mm in June 2015, and began decreasing from June 2015. The maximum recovery of subsidence is \(21\) mm. Since G1501 Highway is under similar geotechnical environment with Lungui Highway, the reasons for this typical seasonal variation are supposed to be related to the hydrogeological conditions and climate factors including precipitation and temperature. From the spatial distribution, deformation generated by both models are generally consistent, with the obvious subsiding bowls distributed in the middle and lower parts of the map. Figure 17 demonstrates the time series deformation of feature point D and E (the corresponding locations in deformation map and Google Maps are shown in Figure 16). Point D was located at the junction of N59 rural road and G1501 Highway. From Figure 16 we can see that the linear model results show a slow subsiding with slight fluctuations, whereas the seasonal model result presents obvious periodic variations. In June 2015, the maximum cumulative deformation of \(-48\)mm occurred. Similar characteristics can be found at point E, as shown in Figure 17b. For the periods of February 2015 to June 2015 and October 2015 to November 2015, the deformation was gradually increasing, with the maximum magnitude of \(-32\)mm. From June to October 2015, apparent subsidence recovery occurred. Figure 15: Time series deformation of G1501 Highway based on seasonal model (referenced to 27 October 2014).