Optimization of 3D Borehole Electrical Resistivity Tomography (ERT) Measurements for Real-Time Subsurface Imaging

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. This study proposes an optimized 3D borehole resistivity tomography (ERT) measurement method to achieve real-time underground grouting imaging and measurement. The abstract of a research paper usually consists of four parts: research background, research methods and content, research results, and conclusions. However, the research methods, content, and results presented in the abstract of this study are extremely vague, and there is no specific statement of the results. Therefore, the reviewer believes that the author needs to improve the abstract section.
2. Although the introduction of this article provides some research status on grouting, it is insufficient. Because the author did not summarize and elaborate on the current research status, deficiencies, and limitations of the research content and techniques used to present this study. The author should appropriately address the shortcomings and deficiencies of the current research in the introduction section of the manuscript. At the end of the introduction, provide the research framework of this manuscript.
3. In the "2. Principles of Electrical Resistance Tomography" section, the author presents the working principle of ERT (electrical resistivity tomography), a geophysical technique used to image the subsurface by measuring resistivity. However, the explanation of this part is purely textual. The reviewer believes that adding a schematic diagram by the author will provide readers and reviewers with a more intuitive understanding of this principle, especially helpful for beginners. 
4. Seepage is a common issue involved in all underground engineering operations and requires monitoring and optimization. Therefore, the first sentence of the introduction needs the support of the following papers to enhance its persuasiveness: Wellhead Stability during Development Process of Hydrate Reservoir in the Northern South China Sea: Evolution and Mechanism; The Crack Propagation Behaviour of CO2 Fracturing Fluid in Unconventional Low Permeability Reservoirs: Factor Analysis and Mechanism Revelation. 
5. In the study, the author used array optimization techniques based on the Jacobian matrix method. What is the progressiveness or advantage of this optimization technology compared with other commonly used optimization technologies? Moreover, Figure 3 presents the cumulative sensitivity matrix (two-dimensional plane) of an optimized array that is not completely symmetrical. From Figure 3, we can see that the cumulative sensitivity matrix is very low in some positions. How to process the measurement results of these locations to meet the requirements of accuracy and precision?
6. In the "Effect of additional equipment" section, the author concludes through comparative experiments that a safe distance of 1 meter should be maintained between the measuring hole and the needle. However, the research results show that the impact is relatively small at a distance of 1 meter, and almost no impact at a distance greater than 1 meter. Would it be better to set the distance between the measuring hole and the needle to be greater than 1m from time to time? But why did the author choose 1m? Subsequently, the author stated that the processing software would be switched to RES3DINV. What is the purpose and purpose of switching to RES3DINV?
7. Will the depth of the target layer detected have an impact on the measurement results? Because the construction depth is not fixed and may be very deep. At this point, the probe may not be fully inserted into the target layer. At this point, how can the accuracy of the measurement results be ensured for the target layer that the probe cannot reach?

Author Response

We thank reviewer 1 for the useful comments and improvements in the MS. We addressed all the comments and suggestions, with the exception comment 3, where we feel that an extra figure (in the 12 already in the text) extends the length significantly. We have some references for details of the ERT method. We hope we have replied in a satisfactory way.

 

1. This study proposes an optimized 3D borehole resistivity tomography (ERT) measurement method to achieve real-time underground grouting imaging and measurement. The abstract of a research paper usually consists of four parts: research background, research methods and content, research results, and conclusions. However, the research methods, content, and results presented in the abstract of this study are extremely vague, and there is no specific statement of the results. Therefore, the reviewer believes that the author needs to improve the abstract section.

We thank the reviewer for this comment. The abstract indeed needed improvement. We re-written the abstract to reflect reviewers comments.

2. Although the introduction of this article provides some research status on grouting, it is insufficient. Because the author did not summarize and elaborate on the current research status, deficiencies, and limitations of the research content and techniques used to present this study. The author should appropriately address the shortcomings and deficiencies of the current research in the introduction section of the manuscript. At the end of the introduction, provide the research framework of this manuscript.

We would like to note that the main message of this work is not imaging grouting, but rather on how to use ERT on monitoring the subsurface (grouting included). We added a section with current status (line 51-65 and references)

 

3. In the "2. Principles of Electrical Resistance Tomography" section, the author presents the working principle of ERT (electrical resistivity tomography), a geophysical technique used to image the subsurface by measuring resistivity. However, the explanation of this part is purely textual. The reviewer believes that adding a schematic diagram by the author will provide readers and reviewers with a more intuitive understanding of this principle, especially helpful for beginners. 

We haven’t;’ included a n extra figure, since we feel we already have 12 in the MS and reader could easily find one in the dozens of published papers.

 

4. Seepage is a common issue involved in all underground engineering operations and requires monitoring and optimization. Therefore, the first sentence of the introduction needs the support of the following papers to enhance its persuasiveness: Wellhead Stability during Development Process of Hydrate Reservoir in the Northern South China Sea: Evolution and Mechanism; The Crack Propagation Behaviour of CO2 Fracturing Fluid in Unconventional Low Permeability Reservoirs: Factor Analysis and Mechanism Revelation. 

 

We added the two references.

 

 

5. In the study, the author used array optimization techniques based on the Jacobian matrix method. What is the progressiveness or advantage of this optimization technology compared with other commonly used optimization technologies? Moreover, Figure 3 presents the cumulative sensitivity matrix (two-dimensional plane) of an optimized array that is not completely symmetrical. From Figure 3, we can see that the cumulative sensitivity matrix is very low in some positions. How to process the measurement results of these locations to meet the requirements of accuracy and precision?

We added a section (189-199) descbirbing the resolution matrix and what it shows. Regarding the areas with low resolution, we added ad section (220-224) expaling what is the area of interest in this example.

6. In the "Effect of additional equipment" section, the author concludes through comparative experiments that a safe distance of 1 meter should be maintained between the measuring hole and the needle. However, the research results show that the impact is relatively small at a distance of 1 meter, and almost no impact at a distance greater than 1 meter. Would it be better to set the distance between the measuring hole and the needle to be greater than 1m from time to time? But why did the author choose 1m? Subsequently, the author stated that the processing software would be switched to RES3DINV. What is the purpose and purpose of switching to RES3DINV?

We agree with reviewer, the definition of safe distance is problematic. We added a section (268-272). For the res3dinf, we added a section (273-275) explaining the reason to switch.

 

7. Will the depth of the target layer detected have an impact on the measurement results? Because the construction depth is not fixed and may be very deep. At this point, the probe may not be fully inserted into the target layer. At this point, how can the accuracy of the measurement results be ensured for the target layer that the probe cannot reach?

The depth of the target layer does not have an impact, as long as the measuring electrodes have similar distance from the target. If for instance the target is on the area of the low resolution, than either change the measuring setup or the location of the electrodes. We consider this a “tailored made” setup, based on what size, depth, resistivity contrast has the target. We added a section on 411-414 to explain this.

Reviewer 2 Report

Comments and Suggestions for Authors

(1) There are many typos in the text. The paper reads like a summary report rather than a rigorous scientific paper. 

(2) Some figures are not clear, such as the legend and text in the figures. There is a lack of necessary illustrations in some photos, where there are so many objects in the photos.

(3)  It still takes 21 mins to obtain an image. Has the injection process continued during the 21 mins. If yes, it is a problem to explain the obtained image as the monitored process is  dynamic.

(4) It is not clear how the authors define the 'resolution' as indicated in line 284.

(5) The inversion software used in this work has been mentioned, however, there is a lack of statement regarding to the settings for inversion. 

(6) Take Figure 12 as an example, how many digits should be used in the legend? It is suggested to keep consistency. 

 

Author Response

We thank reviewer 2 for the useful comments and improvements in the MS. We addressed all the comments and suggestions. We hope we have replied in a satisfactory way.

 

 

 

1. There are many typos in the text. The paper reads like a summary report rather than a rigorous scientific paper. 

We updated the text in various sections to reflect reviewers comments. We hoe it is satisfactory.

2. Some figures are not clear, such as the legend and text in the figures. There is a lack of necessary illustrations in some photos, where there are so many objects in the photos.

We remade figures 1,6,7,8,9,11,12,13

 

3. It still takes 21 mins to obtain an image. Has the injection process continued during the 21 mins. If yes, it is a problem to explain the obtained image as the monitored process is  dynamic.

 

We thank the reviewer for this comment. There is a hardware limitation is this system, to prevents us to stop “stacking measures” and consequently reduce the acquisition time. Yet, if even faster acquisition is needed, someone can further reduce the amount of measures, and sacrificing the spatial resolution further. We added a section in the conclusion to mention this (208-212) to make it clear.

 

4. It is not clear how the authors define the 'resolution' as indicated in line 284.

We agree with reviewer about the confusion with resolution. We added a section (220-224) to describe the inversion resolution and a section (424-426) to describe the spatial resolution.

 

5. The inversion software used in this work has been mentioned, however, there is a lack of statement regarding to the settings for inversion. 

We added a section (184-189) to diusccss the inversion settings.

 

6. Take Figure 12 as an example, how many digits should be used in the legend? It is suggested to keep consistency. 

We updated figure 12

Reviewer 3 Report

Comments and Suggestions for Authors

Below are suggestions and corrections provided for the manuscript titled 'Optimization of 3D Borehole Electrical Resistivity Tomography (ERT) Measurements for Real-Time Subsurface Grouting Imaging'."

The Methods section lacks a coherent structure and logical flow. Details concerning measurement planes, optimization algorithms, and instrumentation are presented in a disorganized manner. It is strongly recommended that the section be subdivided into clearly labeled subsections (e.g., 3.1 Numerical Optimization, 3.2 Laboratory Setup, 3.3 Metal Interference Assessment) to improve readability and comprehension.

The reproducibility of the experimental procedure is questionable, primarily due to inconsistencies in the iron content of the sandbags used in the setup. This heterogeneity introduces significant uncertainty into the resistivity measurements and subsequent interpretation. A more rigorous control or quantification of this variability is necessary.

The manuscript heavily relies on visual interpretation of ERT reconstructions, with limited quantitative support. Key metrics such as normalized root mean square (RMS) error, resistivity contrast ratios, and uncertainty estimates are either insufficiently reported or entirely absent. Inclusion of these quantitative validations is essential for substantiating the findings.

The absence of subheadings in critical sections such as Methods and Results undermines the logical flow and hampers reader navigation. Structured formatting with appropriate subheadings is necessary to enhance clarity and cohesion.

References to figures within the text (e.g., “see Figure 3”) are not well contextualized. Each figure should be integrated more meaningfully into the narrative, with explicit explanations of its relevance to the discussion.

The Conclusion is underdeveloped and contains repetitive content. It should be rewritten in a concise, structured, bullet-point format, clearly restating the main findings and their broader implications for real-time subsurface monitoring and optimization methodologies.

While the manuscript is generally comprehensible, it contains numerous grammatical errors, inconsistent verb tenses, and weak transitions between sentences. Academic tone is sometimes lacking. For instance, statements like “The iron in solution strongly increases electrical conductivity…” should be rephrased in more formal scientific language. A comprehensive professional proofreading is strongly advised.

The discussion lacks sufficient comparative analysis with existing optimization methodologies. The manuscript should explicitly highlight how the proposed approach advances or differs from prior work (e.g., references [11], [12]), both in terms of theoretical contribution and practical implementation.

There are multiple formatting inconsistencies in the reference list, particularly with line breaks and doi presentations. The references should be carefully revised to ensure full compliance with the target journal’s formatting guidelines.

All figures should be provided in high resolution, and figure captions must be sufficiently detailed to enable interpretation without relying solely on the main text.

The manuscript presents a potentially valuable contribution to the field of geophysical imaging and subsurface grouting monitoring. However, it is not currently suitable for publication in its present form. Major revisions are necessary—particularly in terms of methodological clarity, quantitative rigor, language quality, and structural organization. If these issues are addressed comprehensively, the manuscript may be reconsidered for publication following re-review.

Author Response

We thank reviewer 3 for the useful comments and improvements in the MS. We addressed all the comments and suggestions. We tried to change the subsections according to the suggestions. We hope we have replied in a satisfactory way.

 

1. Below are suggestions and corrections provided for the manuscript titled 'Optimization of 3D Borehole Electrical Resistivity Tomography (ERT) Measurements for Real-Time Subsurface Grouting Imaging'."
2. The Methods section lacks a coherent structure and logical flow. Details concerning measurement planes, optimization algorithms, and instrumentation are presented in a disorganized manner. It is strongly recommended that the section be subdivided into clearly labeled subsections (e.g., 3.1 Numerical Optimization, 3.2 Laboratory Setup, 3.3 Metal Interference Assessment) to improve readability and comprehension.

We changed the subheadings (introduced section 4)

 

 

3. The reproducibility of the experimental procedure is questionable, primarily due to inconsistencies in the iron content of the sandbags used in the setup. This heterogeneity introduces significant uncertainty into the resistivity measurements and subsequent interpretation. A more rigorous control or quantification of this variability is necessary.

It’s not possible in this lab scale to have reproducibility, due to the extremely high costs associated with this lab test. In this work, we aim to provide a flowchart on how someone could optimize a monitoring setup, with both numerical and lab results. This work should not be used as is, but rather as a logical flowchart on how to reduce measures. The stings are tailored made  for this setup, but the steps can be applied everywhere. We updated the abstract and conclusions to reflect this comments

 

4. The manuscript heavily relies on visual interpretation of ERT reconstructions, with limited quantitative support. Key metrics such as normalized root mean square (RMS) error, resistivity contrast ratios, and uncertainty estimates are either insufficiently reported or entirely absent. Inclusion of these quantitative validations is essential for substantiating the findings.

We thank the reviewer for these comments. Adding some quantitative support would help to better understand the results. In fact, we were quite troubled with what kind of metrics we could use to show this.

We added lines 326-341 to describe the challenges we faced in this task and why we continued with the visual inspection.

 

 

5. The absence of subheadings in critical sections such as Methods and Results undermines the logical flow and hampers reader navigation. Structured formatting with appropriate subheadings is necessary to enhance clarity and cohesion.

We changed the subheadings (introduced section 4)

 

6. References to figures within the text (e.g., “see Figure 3”) are not well contextualized. Each figure should be integrated more meaningfully into the narrative, with explicit explanations of its relevance to the discussion.

Especially for figure 3, we added a section to describe the resolution matrix (196-206).

We changed all captions. We hoe this is up to reviewers satisfaction.

 

7. The Conclusion is underdeveloped and contains repetitive content. It should be rewritten in a concise, structured, bullet-point format, clearly restating the main findings and their broader implications for real-time subsurface monitoring and optimization methodologies.

We updated the conclusions.

 

8. While the manuscript is generally comprehensible, it contains numerous grammatical errors, inconsistent verb tenses, and weak transitions between sentences. Academic tone is sometimes lacking. For instance, statements like “The iron in solution strongly increases electrical conductivity…” should be rephrased in more formal scientific language. A comprehensive professional proofreading is strongly advised.

We changed some sentences and fixed some typos. We don’t claim that are text is flawless, yet the “a professional proofreading is strongly advised” is a bit unfair. We made several improvements and changes in the whole text, both grammar and spelling.

 We note that the author has published more than 30 papers and has never needed the use of professional proofreading. We leave this comment to the editor.

 

9. The discussion lacks sufficient comparative analysis with existing optimization methodologies. The manuscript should explicitly highlight how the proposed approach advances or differs from prior work (e.g., references [11], [12]), both in terms of theoretical contribution and practical implementation.

 

We added section 51-64, changed the abstract and added the section 429-433 to address those issues, We hope that this is satisfactory for the reviewer.

 

10. There are multiple formatting inconsistencies in the reference list, particularly with line breaks and doi presentations. The references should be carefully revised to ensure full compliance with the target journal’s formatting guidelines.

We updated all references accorind to MDPI standards. .

 

11. All figures should be provided in high resolution, and figure captions must be sufficiently detailed to enable interpretation without relying solely on the main text.

All captions are changed.

 

12. The manuscript presents a potentially valuable contribution to the field of geophysical imaging and subsurface grouting monitoring. However, it is not currently suitable for publication in its present form. Major revisions are necessary—particularly in terms of methodological clarity, quantitative rigor, language quality, and structural organization. If these issues are addressed comprehensively, the manuscript may be reconsidered for publication following re-review.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the paper carefully, and it can be accepted for publication now.

Reviewer 2 Report

Comments and Suggestions for Authors

none

Reviewer 3 Report

Comments and Suggestions for Authors

I have reviewed the revised version of the manuscript titled “Optimization of 3D borehole Electrical Resistivity Tomography (ERT) measurements for real-time subsurface imaging” and find that the authors have addressed my previous concerns. Manuscript can be accepted for publication in this form.