## 4 Conclusions  
This paper presented a study of the TCPInSAR technique in the investigation of the deformation of a linear infrastructure (i.e., the Donghai Bridge in China) based on only four ascending PALSAR images. Compared to the commonly-used PSInSAR technique, the TCPInSAR can identify the coherent points with a small dataset of SAR images and provide reliable deformation measurements without the error-prone phase unwrapping procedure. In addition, TCPInSAR will provide tools to achieve better co-registration between SAR images that are dominated by the low coherent ground objects, such as water. The main conclusions of this study can be summarized as follows:  
1. The results of the experiment have demonstrated the capability and precision of the TCPInSAR method in monitoring linear infrastructure. An average improvement in coherence of about 0.12 has been achieved by the TCP co-registration compared to the conventional globe co-registration. Up to three pixels of the differences can be found between the azimuth offsets derived from identified TCPs and evenly-distributed windows over the whole image, indicating that an un-neglected basis would be caused by the globe co-registration in the sea area. By assuming the TCPs on the island being stable, the RMS of the TCPInSAR-derived deformation rate is 1.2 mm/year, partly due to the single master used in the four interferograms. Since we only employed four PALSAR images with moderate resolution, this is acceptable precision in the monitoring of linear infrastructure.
2. Up to \(-\)1.2 cm cumulative LOS deformation (i.e., a \(-\)2.3 cm/year LOS deformation rate) has been detected in the cable-stayed section of the Donghai Bridge during January and July 2009. It is found that the deformation is highly relevant to the local temperature. This is expected since the longitudinal deformation of a bridge will be caused by the thermal expansion of the cable-stayed part. However, due to the great similarity between the direction of the pier-stayed part of the bridge and the azimuth direction of the used ascending PALSAR data, the longitudinal deformation is underestimated in this study. On the other hand, the detected \(\sim\)1 cm/year deformation of the pier-stayed bridge can be constituted by the transversal deformation associated with the seasonal winds and the tide, as well as the vertical deformation associated with the foundation settlement. Although further investigation should be carried out with more SAR images and environmental materials, this study provides significant insights on the dynamics of the Donghai Bridge.  
The ALOS PALSAR data were provided by the Japan Aerospace Exploration Agency (JAXA). The research was supported by the National Natural Science Foundation of China (nos. 41774023, 41704001, 41674010), the Research Grants Council (RGC) of the Hong Kong Special Administrative Region (Project Nos. PolyU 152214/14E, PolyU 152043/14E), the Science and Technology Project of Hunan Province (no. 2016 SK2002), the Project of Education Department of Hunan Province (no. 16K053), and the Land and Resources Research Project of Hunan Province (No. 2017-13). We appreciate the two anonymous reviewers for their comments and suggestions which greatly improved the manuscript.  
**Author Contributions:** [PERSON], [PERSON] and [PERSON] conceived, designed, and performed the experiments; [PERSON] and [PERSON] contributed to the analysis and discussions of the results; and [PERSON] drafted the manuscript. All authors reviewed and approved the manuscript.  
**Conflicts of Interest:** The authors declare no conflict of interest.