A Low-Cost Web Application System for Monitoring Geometrical Impacts of Surface Subsidence
Round 1
Reviewer 1 Report (New Reviewer)
In this paper, a Web application system is developed to monitor the geometric impact of land subsidence. The satellite images obtained from Sentinel-1 SAR constellation and SBAS-dinSAR are processed by the software package in the SBASdinSAR processing chain to obtain the surface deformation information in the image, which can provide new information data for the monitoring solution. The application effect of the system is illustrated in the Onyeama mine area in Nigeria, where the cumulative horizontal and vertical surface deformation values from 2016 to 2020 are obtained by the application system. Holt-winter analysis, a time-series prediction method, is used to predict the surface deformation value in the next five years based on the deformation data from 2016 to 2020, which can provide a certain reference for geological disaster warning and future development plan. This paper is logical and orderly, and provides a new idea for the formulation of surface subsidence monitoring methods in this area. However, there are still some problems as follows:
1. In line 25-26, the paper does not explain the rules of observation point layout and why the edge of the research area is. Are there many measuring points and few observation points in the middle part?
2. In line 299, the collected secondary data GPS (X,Y,Z) is mentioned. Why is this data not used in the verification of the monitoring results of the Web program and the correctness of the prediction model?
3. In line 375, it is mentioned that the average level deformation in 2016 is (-25.487 = low risk, -35.126 = medium risk and -44.775 = high risk). It is not clear how the risk range is divided here. For example, the low-risk value in 2016 was -25.487, why is the low-risk value in 2020 -28.134?
4. Line 410, the subheading of this subparagraph 4.2 is the result of the average absolute vertical deformation. How can the diagram 9B in it be said to show the average absolute horizontal deformation in 2020?
5. Line 447, 4.3 In summary, the author mentioned the prediction of the absolute horizontal and vertical deformation of the study area in the next five years, but when the current data from 2016 to 2020 is used to predict the future changes in 2021-2025, the prediction sample is not too small? The population expansion, climate conditions and the change of rock strata activity all have an impact on the prediction. In addition, when verifying the correctness of the prediction model, the original data of 2016-2018 is used as the training sample to predict the deformation value of 2019-2020, and then compared with the actual surface deformation value of 2019-2020. This prediction model is originally established with the data of 2016-2020 as the original data. Why not use GPS measurements from 14 observation points obtained in the field to verify the prediction accuracy?
6. The article is to establish a web system to provide early warning information for the surface subsidence, but article is described by the web system for the 2016-2020 the mean surface level in 5 years, vertical deformation value of data, recommendations can also summarize the five years since the trend of the surface vertical and horizontal deformation and the ecological change, the influence of construction safety, In addition, when analyzing the causes of surface deformation, the word "may" is often used, which is not rigorous. It is suggested that in addition to providing vertical and horizontal deformation data, the author can analyze the differences of surface deformation in different years, comprehensively consider the influence of overlying rock changes in mining area, urban expansion speed and climate conditions on surface deformation, and summarize the variation rules. In order to better provide early warning for surface subsidence, make the article more rich and full.
Author Response
Response to Reviewer 1 Comments
Point 1: In line 25-26, the paper does not explain the rules of observation point layout and why the edge of the research area is. Are there many measuring points and few observation points in the middle part?
Response 1: The observation and measuring points were selected at few accessible known locations (major settlements) within the study area with visible evidence of subsidence over the years. It was not systematic but random using a GPS measuring devise to observe the X, Y, Z locations. The few observation points in the middle is because those areas are highly inaccessible and risky. Hence, we have more observation points around the edges (major settlements).
Point 2: In line 299, the collected secondary data GPS (X,Y,Z) is mentioned. Why is this data not used in the verification of the monitoring results of the Web program and the correctness of the prediction model?
Response 2: The GPS X, Y, Z points was first used to extract the deformation values from the DInSAR processed time series map along the years. Thus verifying the observation points along the monitoring results of the Web program. Furthermore, these extracted deformation values was used to make forecast with the prediction model. The correctness or validation accuracy of the prediction model was assessed based on the Mean Absolute Percentage Error (MAPE) (Please see subparagraph 4.5).
Point 3: In line 375, it is mentioned that the average level deformation in 2016 is (-25.487 = low risk, -35.126 = medium risk and -44.775 = high risk). It is not clear how the risk range is divided here. For example, the low-risk value in 2016 was -25.487, why is the low-risk value in 2020 -28.134?
Response 3: To convert the unwrapped phase in radian units to absolute displacements, the Phase to Displacement Operator in SNAP software is applied. It translates the phase into surface changes along the line-of-sight (LOS). The LOS is the line between the sensor and a pixel. Furthermore, the Colour Manipulation Slider Tool in SNAP is applied to highlight areas of low, medium and high risk respectively. Accordingly, positive values mean uplift and negative values mean subsidence of the surface. The risks are divided according to the range of time series deformation values for each year. Depending on the range of deformation values, it may differ year to year; hence the difference in 2016 to 2020.
Point 4: Line 410, the subheading of this subparagraph 4.2 is the result of the average absolute vertical deformation. How come the diagram 9B in it be said to show the average absolute horizontal deformation in 2020?
Response 4: The observation has been noted and corrected accordingly in the revised manuscript.
Point 5: Line 447, 4.3 In summary, the author mentioned the prediction of the absolute horizontal and vertical deformation of the study area in the next five years, but when the current data from 2016 to 2020 is used to predict the future changes in 2021-2025, the prediction sample is not too small? The population expansion, climate conditions and the change of rock strata activity all have an impact on the prediction. In addition, when verifying the correctness of the prediction model, the original data of 2016-2018 is used as the training sample to predict the deformation value of 2019-2020, and then compared with the actual surface deformation value of 2019-2020. This prediction model is originally established with the data of 2016-2020 as the original data. Why not use GPS measurements from 14 observation points obtained in the field to verify the prediction accuracy?
Response 5: The GPS X, Y, Z points was first used to extract the deformation values from the DInSAR processed time series map along the years. Furthermore, these extracted deformation values was used to make only forecast with the prediction model. The GPS X, Y, Z was not used to verify the prediction accuracy because;
- Since the prediction is in the future, there is a possibility that population expansion, climate conditions and the change of rock strata activity, which have impact on the prediction, might change over time.
- These levels of changes cannot be ascertained now until in future and will require further GPS X, Y, Z observations to be made. Using the current GPS X, Y, Z measurement to verify the prediction accuracy of the future without taking cognizance of these levels of changes, which cannot be ascertained now, may report a biased result.
- Our decision to verify the prediction accuracy using the original and actual deformation values was made after reviewing various research material on our prediction model.
Point 6: The article is to establish a web system to provide early warning information for the surface subsidence, but article is described by the web system for the 2016-2020 the mean surface level in 5 years, vertical deformation value of data, recommendations can also summarize the five years since the trend of the surface vertical and horizontal deformation and the ecological change, the influence of construction safety, In addition, when analyzing the causes of surface deformation, the word "may" is often used, which is not rigorous. It is suggested that in addition to providing vertical and horizontal deformation data, the author can analyze the differences of surface deformation in different years, comprehensively consider the influence of overlying rock changes in mining area, urban expansion speed and climate conditions on surface deformation, and summarize the variation rules. In order to better provide early warning for surface subsidence, make the article more rich and full.
Response 6: The response was noted and corrections applied in the revised manuscript. However, because of limitation due to non-availability of data, we may not comprehensively consider influence of overlying rock changes in mining area, ecological change, urban expansion speed and climate conditions on surface deformation, and summarize the variation rules. This is beyond the scope of this work, but will be considered as a recommendation for further studies.
Author Response File: 
Author Response.docx
Reviewer 2 Report (New Reviewer)
Yes, I agree with the authors of the manuscript that the mapping of unstable regions is a very serious problem. Therefore, from this point of view, I consider experimental research to be very relevant. At the same time, I consider the information obtained as part of the research to be valuable.
Although the manuscript is well written, some corrections need to be made and especially in the graphic area. It is necessary to improve the quality of several images, because the text in them is unreadable.
Overall, the contribution is processed at a good level, and with a little graphic editing of the images, it can be published in the Sustainability journal.
I would like to thank the editor for allowing me to review this type of work and the authors for their research efforts.
Author Response
Response to Reviewer 2 Comments
Point 1: Yes, I agree with the authors of the manuscript that the mapping of unstable regions is a very serious problem. Therefore, from this point of view, I consider experimental research very relevant. At the same time, I consider the information obtained as part of the research to be valuable.
Response 1: Experimental research are carried out in controlled conditions under which measurements are made (e.g. laboratory experiments in physics or chemistry). This is an Observational research using Synthetic Aperture Radar (SAR) and Small Baseline Differential Interferometric Synthetic Aperture Radar (SBAS-DInSAR) techniques to develop a Web Application System, which proved early warning for surface subsidence information. Hence, no experiment is possible, but observations are made in uncontrolled or semi-controlled conditions. The source of data as well as observation methods were clearly specified in the manuscript.
Point 2: Although the manuscript is well written, some corrections need to be made and especially in the graphic area. It is necessary to improve the quality of several images, because the text in them is unreadable.
Response 2: The observation has been noted and corrected accordingly in the revised manuscript.
Point 3: Overall, the contribution is processed at a good level, and with a little graphic editing of the images, it can be published in the Sustainability journal.
Response 3: Thanks you for the observation and review.
Point 4: I would like to thank the editor for allowing me to review this type of work and the authors for their research efforts.
Response 4: Thank you for the observation and review.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report (New Reviewer)
The contribution is publishable in its current form.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
I have systematically gone through the manuscript it is good; the authors propose a “low cost web application system for monitoring geometrical impacts of 1 surface subsidence”. It is an interesting issue for the disaster risk reduction. However, the manuscripts need to be improved and carefully revised.
Abstract: This section is concise summary of the research. However, the abstract of the present manuscript is full of general statement. It must highlight methodology and findings.
Methodology: The study proposes use of Sentinel-1 SAR satellite images and Differential Interferometric Synthetic Aperture Radar 16 (DInSAR) for monitoring of land subsidence. Hence, author must discuss source of data download and processing software’s. The web link part is discussed in details.
I also suggest that Fig. 11 and 13 should be added as supplementary materials.
Conclusion section must include the method and findings part. It should avoid general statement.
Written grammar and English should be checked properly before the publication.
Reviewer 2 Report
The authors demonstrate a monitoring platform that provides the results of InSAR results.
It is a topic of interest to researchers in the related area. This study only provides an interaction system, and its contribution to scientific research is limited. This manuscript is more of an analysis of the deformation with the InSAR technique than developing a system.
-It is suggested to revise the abstract. The study focuses on all the geometrical deformation, not only the mining.
-Please improve the quality of Fig1 by increasing the resolution and including the north arrow, scale bar, and annotation.
- The web application model
Please clarify the function of the system. Were the downloading and processing done separately, while the system merely an interface for user interaction?
4.1 Average absolute horizontal deformation results
How is the absolute horizontal deformation calculated? The one stack SBAS-InSAR only provides the measurements in the LOS direction.
