Monitoring and Cause Analysis of Land Subsidence along the Yangtze River Utilizing Time-Series InSAR
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThere are some points I would like to get answers from authors are it is not clear the motivation on the paper on the following questions:
1) Why only 42 Sentinel-1 SLC are selected? I believe that S1 data availability is much larger over the AOI. Please explain and justify the selection of the dataset.
2) Which is their relative orbit? And their time distribution?
3) Are you comparing PSI/SBAS Line-of-Sight directly with Levelling? One of those datasets need to be projected into the same up/down or LoS geometry. Please specify and include this information in the text.
3.1.) if this was not done, it may be the case that the final results are actually fitting better the levelling dataset. please verify
Line 112 : Please correct by changing "spatial resolution of 5m x 20m (azimuthal direction x distance direction)" by "spatial resolution of 20m x 5m (azimuthal direction x range direction) " which is the correct way.
Comments on the Quality of English LanguageSmall editing corrections are needed regarding usage of articles, nothing critical but good to make it review by a native English speaker
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper presents an analysis of land subsidence in the Yangtze River area in Nanjing China, using Time Series InSAR from April 2015 and November 2021. The images were processed with PS-InSAR and SBAS-InSAR methods and the authors compared the results
The studied area is relevant because of its economic growth which has boosted the construction of high buildings and the development of infrastructure, thus studies like those presented in this paper, are welcome to understand the geotechnical challenges that engineers will face.
The paper could be published after the authors improve the paper and reply adequately next questions:
1. As the study presented is on land subsidence the geologic and stratigraphic setting of the zone must be well described.
2. Figure 7 does not allow see the evolution of land subsidence, a figure where the three data of subsidence along the time for each point are plotted is necessary. In this missing figure, also the discrepancies between the data could be easily identified.
3. In section 5.1 "The Influence of Underground Traffic Engineering on Land Subsidence", the authors suggest that Nanjing Metro Line 10 construction and operation have caused land subsidence. They wrote in lines 372-373, and lines 388 -389:
" As illustrated in Figure 11, the area along the Nanjing Metro Line 10 has been undergoing low-speed subsidence since its completion in 2014."
"Therefore, it can be concluded that after the completion of Nanjing Metro Line 10, the ground deformation in this area was consistently sinking year by year."
It is not clear if the construction and operation of the Metro Line caused subsidence, or if the authors want to show that critical infrastructure like the Metro Line is located in the subsidence area.
The authors must rewrite this section to clarify it. In the case that The Metro Line is causing subsidence, the authors must show evidence that does not leave doubts about the subsidence caused by the construction and operation of Nanjing Metro Line 10.
4. The authors stated in lines 405-407:
" Figure 13 demonstrates that 405 as the construction land areas continued to increase annually, the cumulative subsidence of the feature points in the areas also increased, indicating a significant correlation between the two factors."
This suggests that the weight of buildings is causing subsidence, which implies that the subsidence area limit should correspond with the urban area over time. The authors must prove this to confirm the proposed correlation in Figure 13.
5. Point 3 in the conclusion section, line 450-452: " Analyzing the factors that caused the land subsidence in this area, it was found that the subsidence was the result of a combination of many factors, such as the construction and operation of subway engineering projects, the yearly increase of ground buildings area, and the fragile geological conditions."
The authors do not present conclusive evidence of the contribution of the construction of buildings and infrastructure to land subsidence. Figure 11 does not show a strip of subsidence along the Metro Line, and Figure 13 is inconclusive, as I stated in comment point 4. They must show separately the contribution of each factor.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript uses 42 Sentinel-1A images from 2015 to 2021 to monitor the land subsidence along the Yangtze River in Nanjing by time-series InSAR technology, and obtains the deformation rate of the study area and the deformation field of the typical area. By analyzing the causes, it is found that underground engineering, ground load and fragile soil are the main causes of land subsidence. This research has certain reference value for similar fields. I agree with the acceptance of the manuscript, but there is a question.
Since there are already leveling points to verify the monitoring accuracy, please explain why two time-series InSAR methods are used to monitor the deformation of this region?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe main concerns are covered in this version 2 so the paper can provides now a better methodological comparison among the different techniques. Thank you for that.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe formulated questions were answered, the doubts on ambiguous paragraphs were clarified and the observations were attended.
