Leveraging Multi-Temporal InSAR Technique for Long-Term Structural Behaviour Monitoring of High-Speed Railway Bridges
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript utilizes high-resolution TerraSAR-X imagery and PS-InSAR technique to monitor railway bridges. By analysing the monitoring results in conjunction with temperature, concrete properties, and levelling measurements, the study demonstrates the effectiveness of the InSAR method in monitoring concrete railway bridges. By analysing the deformations of the two bridges, the study found recurring arch-shaped uplift along the line, which can be decomposed into long-term deformation caused by concrete structure and properties, and periodic deformation closely related to temperature. This manuscript provides an example for time-series InSAR monitoring of large infrastructures such as railways and bridges, with a rigorous analysis incorporating multiple factors. However, there are still some deficiencies, and detailed review comments are as follows:
In the introduction section, it is recommended that the authors include a description of the manuscript’s structure at the end of this section to help readers grasp the overall organization of the paper. Also, the review of relevant literature is too brief. It is suggested to add more content to enhance the manuscript's professionalism.
Line 207, “This study employs the PS‐InSAR technique, an approach capable of estimating surface displacements.” Regardless of which PSI method is used, it is advisable to cite the original authors’ literature.
When introducing experimental datasets and processing steps, it is advisable to indicate how many SAR images were used and how many interferograms were generated.
Line 274~281, “Parameters such as look scale, coherence threshold, and signal‐to‐noise ratio (SNR) directly influenced the final PS density. Initially, we expected more accurate analysis with a higher number of PSs; however, setting these parameters too low resulted in an excessive number of PSs, making it difficult to distinguish the bridge and introducing outliers with low coherence. Additionally, calculation time increased geometrically. Through trial and error, we determined an appropriate PS density. Figure 10 compares results by reflecting these differences. Figures 10 (a), (b), and (c) show images of the same area with low, moderate, and high filtering effects, respectively, after adjusting the parameters.” Can you specify which parameters were adjusted? Are there any metrics that can show the advantages and disadvantages of these adjustment strategies?
Line 291~294, “We set minimum and maximum velocity values to 1.3 times the most drastic subsidence velocity, based on survey records. Records of very drastic displacement exceeding set values or track maintenance and management were excluded from the PS‐InSAR results.” Is it appropriate to use only the maximum recorded value as a reference? What if the abnormal deformation of ground targets exceeding 1.3 times the recorded value is related to a hazard? Excluding it introduces monitoring blind spots and risks.
Figure 12, it is recommended to use gradient colors to reflect the deformation rates of each PS, rather than just plotting the positions of the PSs. This will help readers quickly identify areas with significant deformation on the bridge.
Line 356, “Figures 13 and 14 show the PS‐InSAR along the LOS direction of Bridges A and B.” What does “the PS-InSAR along the LOS direction” mean? Figure 13 should be the cumulative deformation profile of PS targets along the bridge.
Figure 15 and figure 17, what are the specific positions of spans ‘a’, ‘b’, ‘c’ and ‘I’, ‘ii’, ‘iii’ on the bridge?
Line 409~410, “The PS‐InSAR analysis results on the centre of spans confirmed a constant trend being repeated on an annual basis in the time‐series data of the six spans.” Please use mathematical tools specifically designed for periodic analysis, such as FFT or CWT, to quantify such periodic signal related to temperature.
Figure 19, how is this long term deformation calculated?
Line 528~531, “We compared the average displacements we found with the results of a numerical analysis, discovering a notable degree of consistency: 78.2% for Bridge A and 154% for Bridge B. This reinforces our findings and attests to the potential reliability of our approach.” This part of the conclusion does not exist in the manuscript, please add it.
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
The article presents the context of the problem to be solved in a clear and objective manner. It has potential for publication, as the subject is of interest, since the topic in question affects engineering works and railway systems. However, the final structure of the text should be reviewed, especially about presenting the conclusions clearly and separately from the discussions.
The article should undergo a review and below are some points to be observed by the authors:
– In item “2.2. Nature of the Post-tensioned Pre-stressed Concrete (PSC) Box Bridge”, the authors state that “External forces on the girder, such as driving load, wind load, and earthquakes, although brief compared to the satellite revisit cycle, are not suitable for InSAR analysis.”. Could the authors explain this statement better?
– In item “3.1. Data Acquisition”, the authors present the characteristics of the images used for the work. Is there any specific reason for collecting images in VV polarization? Is it possible to discuss this in the text?
– What software was used to process the TSX images? Could a description and respective reference be included in the text?
– Figure 11 presents a comparison between the results of the parametric analysis and field survey. How were the field data obtained and how accurate is it? Are the field data and the results extracted from the TSX images in the same reference system (ellipsoid or geoid)?
– In Figure 12, could the authors increase the size of the “PS” and apply a color (e.g., red) for better representation?
– The authors present a discussion about the results achieved and should have presented the conclusions separately in the text. I suggest that a specific section be created for the conclusions of the work and recommendations for future work.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this paper, the time series InSAR is used to monitor the deformation of the bridge, and the deformation of the whole bridge and different spans is obtained. At the same time, the influence of temperature on the deformation of the bridge is analyzed. The paper is innovative, but it’s recommended to modify the paper as follows :
1. The author should prove that the accuracy can be 0mm in the Line 83;
2. Figure 7 The author needs to give some explanation on the differences between the left picture and the right picture, and mark the number；
3. There are errors in the description of Figure 9, which need to be verified and corrected, and it is recommended to number the two images；
4. For Fig.10, it is recommended to mark the specific positions from the start point to the end point in Figure 11；
5. It is suggested that the values of parameters A, B and C set in Figure 11 and the bridge deformation should all be represented by lines for comparative analysis；
6. All graphs in this paper are recommended to use true color images；
7. It is suggested that all the interference deformation points in the paper should be displayed by color points according to the size of deformation；
8. It is recommended to mark span a, b, c and i, ii, and iii in Fig. 14.
Comments on the Quality of English LanguageThis paper is readable.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have revised the manuscript according to my comments, and my concerns are solved.
Comments on the Quality of English LanguageThe language is OK.
Reviewer 3 Report
Comments and Suggestions for AuthorsThere are no further suggestions for revision of this paper.
