InSAR Monitoring Using Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) Techniques for Ground Deformation Measurement in Metropolitan Area of Concepción, Chile

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors employed multi-temporal InSAR to monitor the deformation of Concepción, Chile. They utilized two types of InSAR techniques, namely PSI and SBAS, and conducted a comparative analysis of the results. By leveraging data from both ascending and descending satellite paths, two-dimensional displacements were derived. The outcomes hold the potential to contribute significantly to the assessment of ground deformation within the Metropolitan area and urban planning. The manuscript is comprehensive, and with minor adjustments, it can be considered for publication.

 

1）In Line 73, the word "ad-dressed" should be corrected to "addressed" to eliminate the hyphenation issue and enhance readability.

 

2）In Figure 5, the authors should review the workflow. The term "temporal phase unwrapping" appears before "spatial phase unwrapping." It's important to ensure that the sequence of processing steps is logically structured.

 

3) The figures within the manuscript would benefit from higher resolutions, especially Figure 7. Enhanced clarity in these figures is essential for readers to obtain accurate information.

 

4）In Lines 230 and 231, the deformation rates are described as -22.4 mm/yr and 4.6 mm/yr, while Figure 7(b) labels them as -22.5 mm/yr and 4.5 mm/yr. The authors should harmonize these values for consistency.

 

5）The red lines in Figure 7(b) are not clearly explained. The authors should provide a legend or description to clarify their significance.

 

6）For Figures 8 and 9, it is advisable to maintain a consistent range for colorbars to facilitate comparisons.

 

7) In Figure 11, "Frecuencia" should be corrected to "Frequency".

Comments on the Quality of English Language

In Line 73, the word "ad-dressed" should be corrected to "addressed" to eliminate the hyphenation issue and enhance readability.

In Figure 11, "Frecuencia" should be corrected to "Frequency".

Author Response

Dear reviewer 1,

We appreciate your review,

We have responded to all your suggestions and comments,

we hope we have reached your requirements,

Best regards!!

1）In Line 73, the word "ad-dressed" should be corrected to "addressed" to eliminate the hyphenation issue and enhance readability.

Thank for the comment, Corrected !!!

2）In Figure 5, the authors should review the workflow. The term "temporal phase unwrapping" appears before "spatial phase unwrapping." It's important to ensure that the sequence of processing steps is logically structured.

Thanks, Corrected!!

3) The figures within the manuscript would benefit from higher resolutions, especially Figure 7. Enhanced clarity in these figures is essential for readers to obtain accurate information.

 Corrected (Attached .zip Figures high resolution)

4）In Lines 230 and 231, the deformation rates are described as -22.4 mm/yr and 4.6 mm/yr, while Figure 7(b) labels them as -22.5 mm/yr and 4.5 mm/yr. The authors should harmonize these values for consistency.

Thank for the comment, we corrected the typo in the text with the correct values already written in the Figure 7.

5）The red lines in Figure 7(b) are not clearly explained. The authors should provide a legend or description to clarify their significance.

The red lines represent the regression straight lines estimated basing on the GNSS data (blue dots), we updated the Figure’ caption, thank you

6）For Figures 8 and 9, it is advisable to maintain a consistent range for colorbars to facilitate comparisons.

The constant range of the color bars indicate different movements, so different colors for LOS, Up, horizontal displacement.

7) In Figure 11, "Frecuencia" should be corrected to "Frequency".

Thanks, Corrected!!!

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Comments can be found in the attached document.

Comments for author File: Comments.pdf

Author Response

Dear reviewer 2,

We appreciate your review,

We have responded to all your suggestions and comments,

we hope we have reached your requirements,

Best regards!!

Reply comment 1-2

Right, thanks for the comment, we added a paragraph to clarify that in section 2.4 at lines 245-247

Reply comment 3

Correct, sorry for the typo…indeed the acquisitions comes from both Sentinel 1A and Sentinel 1B for both ascending and descending geometries. We updated Table 1, and global coverage of sentinel 1 in LATAM, up to 12 days of review time

https://sentinels.copernicus.eu/web/sentinel/missions/sentinel-1/satellite-description/geographical-coverage

 

Reply comment 4

Sorry, corrected!!

 

Reply comment 5

Added caption figure 10a, Thanks!!

 

Reply comment 6,

Sorry, deleted

Thank you!!

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The paper of Giorgini et al. deals on the issue of comparing two techniques for processing DInSAR data in a rigorous and sufficiently clear manner. Although they describe a methodology that has already been consolidated for many years (the two processing chains SBAS and STAMPS, there is extensive scientific literature on this topic) and the calibration of the results with a GPS station, the paper is clearly written with a good illustration of the obtained results, therefore I suggest the publication on RS.

Author Response

Dear reviewer 3,

We appreciate your review,

We have responded to all your suggestions, comments and extensive modifications to English.

we hope we have reached your requirements,

Best regards!!

Reviewer 4 Report

Comments and Suggestions for Authors

This paper processes Sentinel-1 InSAR data over Concepcion, Chile using two well-known techniques to understand the patterns of ground deformation. The deformation is loosely and unconvincingly related to new measurements of the horizontal-to-vertical spectral ratio (HVSR) of soil properties in a small part of the city.

I have some major issues with this paper as it stands, which are detailed below:

1.       The horizontal-to-vertical spectral ratio (HVSR) measurements are important. Were these new measurements done by you? If so explain how. It’s the comparison to the InSAR velocities that I think is not correct for this paper. Perhaps publishing them separately would be more appropriate? The site conditions details how the velocity of seismic waves are affected by soil properties. I don’t see a clear justification (geophysical or otherwise) as to how this is relevant to ground deformation measured using InSAR. Since this is the main aim of the paper, I would like there to be a strong justification for making the comparison. And then a rigorous comparison between measured InSAR velocities and soil types/properties.

2.       Another important issue I have is that all you have done is presented velocity maps using two different well-known techniques on the same data. I don’t see an extensive comparison of the similarities and differences and a discussion on why these arise.

3.       Lines: 332-33: There is no clarity on what you are talking about. “characterized by low (0.84 333 Hz) to high frequencies (2.50 to 3.46 Hz as shown in the figure”. What are you talking about here?

4.       Paragraph between lines 338-348 feels important but I don’t understand what you are saying here.

5.       Table 4: Where are these measurements taken with respect to where you have InSAR measurements?

6.       You mention the impact of subduction several times in the manuscript. But there is no discussion about how subduction processes impact measurements of vertical deformation, how this may vary in space and the relative impact of this with respect to anthropogenic activity, such as ground water extraction. For example, is the measured subsidence related to long-term postseismic relaxation or interseismic loading, or none of the above?

7.       The introduction is far too long. We do not need the history of InSAR techniques as this has been covered extensively in other papers/books. Please just state what you are doing and why.

8.       Why did you use two different resolutions for the SBAS and PSI processing? For a fair comparison I would also average the PSI results to the same resolution.

9.       What did you do with the north component of motion when doing the decomposition? Int eh GPS velocities in Figure 7 show that they are significant.

Minor points:

1.       Section 1.2 / Figure 1: where are the GNSS data from? Are these data you collected as part of this research or obtained from other sources? What reference frame are they in? If the GNSS are from another source, please cite and explain.

2.       Figure 2: Please cite the source of the geological units. Unless this is from your own field mapping, in which case please say so.

3.       You have not explained what HVSR is.

4.       Fig 8: Please use the same scale for the PSI and SBAS comparison.

5.       Line 285 spelling: lite -> light

6.       Figure 10. The labels for a) and b) do not match the figure panels

7.       Table 3: I’m not sire if you have your min-mean-max velocities in the right order for the Up velocities

8.       Figure 9: Please flip the scale so the minimum value is at the bottom.

9.       Figure 10. Please check if the scale for the vertical velocity is correct

Comments on the Quality of English Language

Extensive English language checks required.

Author Response

Dear reviewer 4,

We appreciate your review,

We have responded to all your suggestions, comments and extensive modifications to English.

we hope we have reached your requirements,

Best regards!!

1. The horizontal-to-vertical spectral ratio (HVSR) measurements are important. Were these new measurements done by you? If so explain how. It’s the comparison to the InSAR velocities that I think is not correct for this paper. Perhaps publishing them separately would be more appropriate? The site conditions details how the velocity of seismic waves are affected by soil properties. I don’t see a clear justification (geophysical or otherwise) as to how this is relevant to ground deformation measured using InSAR. Since this is the main aim of the paper, I would like there to be a strong justification for making the comparison. And then a rigorous comparison between measured InSAR velocities and soil types/properties.

Thank you for your comments and suggestions, we believe that HVSR measurements are important as strain is directly related to stiffer soils where frequencies tend to be lower, therefore we believe this can open new perspectives by expanding testing areas HVSR in areas prone to deformation.

The tests were carried out by us during the period April-May 2023 in 20 places in the city of Concepción (lines 372-380), where the following points stand out with their respective frequencies (Table 4). Noise measurements were recorded with triaxial geophones (Tromino Engy 3G) provided by the engineering faculty of the University of Concepción, which allow recording environmental vibrations on the ground surface in North-South, East-West and vertical directions. .

2. Another important issue I have is that all you have done is presented velocity maps using two different well-known techniques on the same data. I don’t see an extensive comparison of the similarities and differences and a discussion on why these arise.

Thank you for the comment. We improved the paper by adding a couple of paragraphs in sections 3.1 (lines 297-300) and 3.2 (lines 322-325)

3. Lines: 332-33: There is no clarity on what you are talking about. “characterized by low (0.84 333 Hz) to high frequencies (2.50 to 3.46 Hz as shown in the figure”. What are you talking about here?

Improved paragraph explained, Added line 344-352 Thanks.

4. Paragraph between lines 338-348 feels important but I don’t understand what you are saying here.

Corrected paragraph 339-343

5. Table 4: Where are these measurements taken with respect to where you have InSAR measurements?

Thanks for the comments, the horizontal-to-vertical spectral ratio (HVSR) measurement points are indicated with A, B,C,D,E and F, with their respective locations in Figure 10b and 10c.Thanks!!

6. You mention the impact of subduction several times in the manuscript. But there is no discussion about how subduction processes impact measurements of vertical deformation, how this may vary in space and the relative impact of this with respect to anthropogenic activity, such as ground water extraction. For example, is the measured subsidence related to long-term postseismic relaxation or interseismic loading, or none of the above?

Thanks for the comments, the paper is contextualized in the Chilean subsuction area described in Fig1. This region was affected by the 8.8 Mw earthquake in 2010, which caused extensive damage to the metropolitan area and infrastructure, in addition to prolonged post-seismic deformation, which has developed in recent decades through the coupling of the plates, that is why we are interested in concentrating our work in this area.

7. The introduction is far too long. We do not need the history of InSAR techniques as this has been covered extensively in other papers/books. Please just state what you are doing and why.

Improved introduction writing, Thanks.

8. Why did you use two different resolutions for the SBAS and PSI processing? For a fair comparison I would also average the PSI results to the same resolution.

As we stated in section 2.3 (lines 201-206), despite the fact that both PSI and SBAS computation are based on the same dataset, the SBAS technique inherently provides outputs on a regular grid 90m x 90m, whereas PSI outputs are given on an irregular spatial distribution at a maximum density given by the raw data pixel dimensions. Therefore, some of the results are bounded to be spatially inhomogeneous for reasons intrinsic to the processing approach. Nevertheless, for certain direct comparisons like in section 3.1, we averaged the PSI value into the cells given by the SBAS grid to have coherent values.

9. What did you do with the north component of motion when doing the decomposition? Int eh GPS velocities in Figure 7 show that they are significant.

Dear reviewer, as we now clarify in section 2.4 at lines 247-249, the SAR technique is inherently almost blind to displacements ongoing along the north-south direction because of the acquisition geometry. Therefore, it is meaningless to apply GNSS correction along a direction for which we have no significant data.

Minor points:

1. Section 1.2 / Figure 1: where are the GNSS data from? Are these data you collected as part of this research or obtained from other sources? What reference frame are they in? If the GNSS are from another source, please cite and explain.

Added caption and reference 

Yáñez-Cuadra, V., Moreno, M., Ortega-Culaciati, F., Donoso, F., Báez, J. C., & Tassara, A. (2023). Mosaicking Andean morphostructure and seismic cycle crustal deformation patterns using GNSS velocities and machine learning. Frontiers in Earth Science, 11, 1096238.

Moreno, M., Melnick, D., Rosenau, M., Baez, J., Klotz, J., Oncken, O., ... & Hase, H. (2012). Toward understanding tectonic control on the Mw 8.8 2010 Maule Chile earthquake. Earth and Planetary Science Letters, 321, 152-165.

2. Figure 2: Please cite the source of the geological units. Unless this is from your own field mapping, in which case please say so.

Added reference

SERNAGEOMN—National Geology and Mining Service, Source Open Geological Map of Chile. Available online: https://www.sernageomin.cl/geologia/ (accessed on 15 May 2023).

3. You have not explained what HVSR is.

Added acronym, thanks!!

4. Fig 8: Please use the same scale for the PSI and SBAS comparison.

Corrected, Thanks!

5. 5.Line 285 spelling: lite -> light

Corrected, Thanks!

6. Figure 10. The labels for a) and b) do not match the figure panels

Corrected, Thanks!

7. Table 3: I’m not sire if you have your min-mean-max velocities in the right order for the Up velocities

Correct, thank you for this comment. We definitely corrected the typo by updating the table with the correct numbers.

8. Figure 9: Please flip the scale so the minimum value is at the bottom.

Done, thank you.  

10. Figure 10. Please check if the scale for the vertical velocity is correct

Corrected, Thanks!

Author Response File: Author Response.docx