## 4 Results and Discussion  
### Lungui Highway  
Figure 5 shows the linear velocities comparison between the linear model and seasonal model. Figure 5a illustrates the mean value of all the temporal deformation velocities between every two time-adjacent SAR acquisitions obtained from the linear model. For comparison, the corresponding linear average velocity for the seasonal model is calculated through the LP deformation components acquired, according to Equation (3). As shown in Figure 5, linear model and seasonal model results show good agreement in spatial distribution, with the color ranging from light green to orange, and deformation rates generally ranging from \(-35\) mm/yr to \(5\) mm/yr. It can be seen that the fast subsiding points densely distribute in the lower left corner and the upper right part for both models, with the velocity mainly ranging from \(-25\) mm/yr to \(-45\) mm/yr. The maximum deformation rate is up to \(-39\) mm/yr for the linear model. The main difference between the two images are two areas (see the area within solid rectangle A,B in Figure 5a). The maximum subsidence rate detected at subsidence bowl A is \(-38\) mm/yr from the linear model, whereas it is only \(-24\) mm/yr from the seasonal model. In contrast, at the subsidence bowl B, the linear model shows smaller area, whereas the subsidence rate of the seasonal model is more serious, with a maximum value up to \(-45\) mm/yr. Figure 4: Average coherence maps. (**a**) Lungui Highway; (**b**) G1501 Highway. Figures 6 and 7 show the time series deformation generated from the linear model and seasonal model, respectively. From the spatial distribution, the results of the linear model and seasonal model are consistent, with two main obvious subsidence bowls in the upper right and lower left of the area, respectively. From the temporal variation, we can see both the results show serious fluctuation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Deformation Model** & **Subsidence Increase Period** & **Subsidence Decreasing Period** & **Maximum Subsidence** & **Maximum Fluctuation** \\  & **(yyyy/mm/dd)** & **(yyyy/mm/dd)** & **(mm)** & **(mm)** \\ \hline Linear & 2014/11/18–2015/08/31 & & \(-\)71 & \(67\) \\ model & 2015/11/05–2015/11/27 & & & \((2015/08/31)\) & \(67\) \\ Seasonal model & 2014/11/18–2015/06/26 & & & \(-\)66 \\  & 2015/09/22–2015/11/27 & 2015/06/26–2015/09/22 & & \(62\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of experimental results between the linear model and seasonal model. Figure 5: Average linear velocities of Lungui Highway. **(a)** Linear model; **(b)** Seasonal model. Figure 6: Time series deformation of Lungui Highway based on the linear model (referenced to 27 October 2014). The quantitative comparison of each highest oscillation, including subsidence increasing, subsidence decreasing period, the maximum subsidence, and fluctuations, are shown in Table 2. For the result of the linear model, the subsidence was increasing from 18 November 2014 to 31 August 2015, whereas a decreasing trend occurred from 22 September 2015. The peak subsidence occurred at 31 August 2015, with a magnitude of -71 mm. The overall deformation mainly distributes within the range of -20 to 0 mm. For the result of the seasonal model, similar subsiding increasing trend can be found until 25 June 2015. However, from 26 June 2015 to 22 September 2015, the seasonal results showed an obvious jump in subsidence reduction, with the maximum subsidence recovery of 32 mm. From October 2014 to November 2015, another subsiding period started. The key reason for this temporal periodical variation is supposed to be related to the local hydrogeological conditions discussed as follows. From Figure 2c, we can see the densely distributed ponds along this route (small dark rectangles). Most of those areas are breeding ponds, near Ronggui Channel and Shunde Branch Channel.