Extraction of Remote Sensing Alteration Information Based on Integrated Spectral Mixture Analysis and Fractal Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The text femonstrates scientific mastery of the subject. Very well written. Congratulations. 

 

Comments for author File: Comments.pdf

Author Response

Dear reviewer 

Thank you very much for your positive feedback and helpful suggestions on our manuscript.

We have carefully checked all the highlighted points and corrected the errors accordingly. Additionally, regarding the term "endmembers," we have confirmed that the correct and widely accepted form in remote sensing literature is indeed "endmembers," rather than "end members."

Thank you once again for your time and valuable input.

Sincerely.
Kai Qiao

Reviewer 2 Report

Comments and Suggestions for Authors

This paper needs in the geology section a section on the spectroscopy of the minerals in section. The lack of referencing the minerals in the host lithologies and the alteration minerals in section 2 is distressing.

 

I am not sure you understand economic geology, alteration mineralogy, and mineral spectroscopy with the choice of fractals for isolating the regions of interest. Better approaches would be using decision trees, clustering algorithms, and other machine learning approaches instead of fractals. These approaches are more in line with how alteration minerals, economic geology, mineral exploration are pieced together by exploration geologists and would have a greater impact and adoption by the wider community.

 

Figure 1: It is hard to determine the workflow from this figure as this figure does not describe a linear process or an integrated process. This figure needs to either be in a data science workflow or a remote sensing / image processing workflow. This is neither.

 

Section 2.1: Need to list the minerals associated with each of the rock formations. This can be summarized in table. 

 

Figure 3: needs latitude and longitude on the bounding images.

 

Line 179: The mixing equation should be properly rendered. This is not the proper representation of the spectral mixing equation in vector notation or mathematical notation. There is no summation, please find the correct equation to represent spectral mixing using greek letters and subscripts. The other options are representations in vector notation. 

 

Lines 180-184: Find the original SMACC paper by Gruninger circa 2004 and reference appropriately. Your reference is derivative. This will help your writing of the paragraph.

 

Lines 185-190. Your reference is for Vertex Component Analysis and not SMACC. You are conflating two similar approaches. Read the previous recommendation.

 

Line 202: Consider rephrasing since Mandelbrot introduce the concept of fractals in the 1983 (see your reference) not the 1970’s.

 

Line 220: Need equation number. 

Line 222: Need equation number.

Line 225: Provide equation for correlation coefficient to prevent confusion with Pearson’s R.

 

Line 242: Which Linear transformation? This should be specified. Did you run PCA or MNF prior to SMACC?

 

Line 267: This can be brought out as an equation.

 

Table 2: My interpretation of the table is that DN1 corresponds to Band 2. DN typically represents the digital number within a band these formula can be readily misinterpreted. My suggestion is replace DN with Band2(DN) etc to clarify the band that is being used in the equation. Also add reference to F3, F4, F6, into the table either in the caption or as a legend to the table.

 

Section 4.2: Really should be in the geology section. The reference to the USGS spectral library should be in the methods section if used for spectral mapping.

 

Line 290: This is not properly referenced. Since the USGS spectral library is used, it needs to be properly referenced.

 

Figure 7: Highlight the Fe, OH-, CO3 2-, groups on the plots. This show the regions of interest in the spectral features.

 

Lines 298-300: This needs clarification that PCA was conducted on a subset of the 9 bands, to 4 bands, Band 2, 4, 8A, and 11 also explaining the subletting for the other channels as well. This is not clear.

 

Lines 342-347: Create a table with the mean and standard deviation and mean + N*Sigma for each image. This will document the words provided. 

 

Figure 8: 

Line 349: place the (a), (b), etc prior to the mention. For example, (a) Iron-stained.

 

Figure 10:

Line 391: See recommendation for Line 349

 

Lines 398-400: This description of the units and their mineralogy should reside in the geology section. 

 

Figure 11 (Line 432). Needs latitude and longitude on the boundaries (Figures 10, 8, 6, 3). It would be nice to see a partial transparency of Figure 2 underlain on this figure. If not underlain, a side by side of the geology map (Figure 2) with the result (Figure 11).

 

Line 435: Plot the traverse on figure 11.

 

Figure 12: Describe if these photomicrographs are microscope, hand sample, reflected light, SEM and/or EPMA images.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English is okay.

Author Response

Dear reviewer

Re: Manuscript ID: minerals-3716081

Thank you for your comments concerning our manuscript entitled "Extraction of Remote Sensing Alteration Information Based on Integrated Spectral Mixture Analysis and Fractal Analysis". Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the revised manuscript file. Revisions in the text are shown using a red highlight for additions and a strikethrough font for deletions. The responses to the reviewer's comments are marked in red and presented as follows.

In the following, I will respond to each of the suggestions and questions raised by the reviewers.

Q1. Suggestions from reviewer: It is hard to determine the workflow from this figure as this figure does not describe a linear process or an integrated process. This figure needs to either be in a data science workflow or a remote sensing / image processing workflow. This is neither.

Response: Thank you for your valuable comment. We fully agree with your suggestion that the original Figure 1 lacked clarity in presenting a coherent and linear workflow. In response, we have removed Figure 1 from the revised manuscript to avoid confusion and improve the overall presentation. We appreciate your insight, which helped enhance the structure of our work.

Q2. Suggestions from reviewer: Section 2.1: Need to list the minerals associated with each of the rock formations. This can be summarized in table. 

Response: Thank you for your valuable suggestion. In response, we have added a detailed description of the representative minerals associated with each rock formation directly in Section 2.1 of the revised manuscript. While we did not present the information in a separate table, the mineralogical associations have been clearly stated in the text to enhance clarity and comprehensiveness. We hope this revision adequately addresses your concern.

Q3. Suggestions from reviewer: Figure 3: needs latitude and longitude on the bounding images. (Line 432). Needs latitude and longitude on the boundaries (Figures 10, 8, 6, 3).

Response: Thank you for your helpful suggestion regarding including latitude and longitude grids on the boundary of Figures 3, 6, 8, and 10. We fully understand the importance of geographical reference for improving interpretability. However, due to confidentiality regulations imposed by our institution's science and technology department, geospatial coordinates such as latitude and longitude are restricted from publicly disseminated figures. Therefore, we regret that we cannot include this information in the revised manuscript. We appreciate your understanding on this matter.

Q4. Suggestions from reviewer: Line 179: The mixing equation should be properly rendered. This is not the proper representation of the spectral mixing equation in vector notation or mathematical notation. There is no summation, please find the correct equation to represent spectral mixing using greek letters and subscripts. The other options are representations in vector notation.

Response: Thank you for your valuable suggestion. In response to your comment, we have revised the spectral mixing equation to ensure it is properly expressed using appropriate vector and mathematical notation, including Greek letters and subscripts. Specifically, we have included the summation form to accurately reflect the linear spectral mixture model (LSMM), which is commonly used in hyperspectral unmixing analysis. The corrected equation has been incorporated into the revised manuscript (see Line 218). We appreciate your guidance in improving the scientific rigor and clarity of the manuscript.

Q5. Suggestions from reviewers: Lines 180-184: Find the original SMACC paper by Gruninger circa 2004 and reference appropriately. Your reference is derivative. This will help your writing of the paragraph.

Response: We are grateful for the suggestion. In response, we have revised the citation and included the original SMACC paper by Gruninger et al. (2004) as Reference [48] in the revised manuscript. This adjustment ensures the originality and accuracy of the referenced source. We also refined the related paragraph better to reflect the theoretical basis of the SMACC model. Thank you again for pointing this out.

Q6. Suggestions from reviewer: Lines 185-190. Your reference is for Vertex Component Analysis and not SMACC. You are conflating two similar approaches. Read the previous recommendation.

Response: Thank you for your valuable feedback. We acknowledge the confusion between the original manuscript's SMACC (Sequential Maximum Angle Convex Cone) and VCA (Vertex Component Analysis) approaches. Following your recommendation, we have thoroughly reviewed the relevant literature and corrected the citation accordingly. The revised manuscript now properly attributes the SMACC algorithm to Gruninger et al. (2004), and the incorrect reference to VCA has been removed. The associated paragraph has also been updated to describe the SMACC methodology accurately. We appreciate your careful review, which has helped improve the clarity and accuracy of our manuscript.

Q7. Suggestions from reviewer: Line 202: Consider rephrasing since Mandelbrot introduce the concept of fractals in the 1983 (see your reference) not the 1970's.

Response: Thank you for pointing out this important detail. We have corrected the statement in the revised manuscript to accurately reflect that the concept of fractals was formally introduced by Mandelbrot in 1983, as referenced in our citation. We appreciate your careful review and constructive suggestions, which helped improve the accuracy of our historical context.

Q8. Suggestions from reviewer: Line 220: Need equation number; Line 222: Need equation number.

Response: Thank you for your helpful suggestion. We have added the appropriate equation numbers to the equations referenced on lines 220 and 222 in the revised manuscript to ensure clarity and consistency in presentation.

Q9. Suggestions from reviewer: Line 225: Provide equation for correlation coefficient to prevent confusion with Pearson's R.

Response: Thank you for the valuable comment. To address this concern, we have revised the manuscript to specify the statistical metric used clearly. In particular, the term "correlation coefficient" has been replaced with "coefficient of determination (R²)" to avoid confusion with Pearson's correlation coefficient. This clarification has been implemented in Lines 260–264 of the revised manuscript.

Q10. Suggestions from reviewer: Line 242: Which Linear transformation? This should be specified. Did you run PCA or MNF prior to SMACC?

Response: Thank you for your helpful comment. In response, we have clarified the preprocessing step preceding the SMACC algorithm. Specifically, we applied the Minimum Noise Fraction (MNF) transformation to the hyperspectral data before performing endmember extraction with SMACC. This has now been explicitly stated in Lines 279–281 of the revised manuscript.

Q11. Suggestions from reviewer: Line 267: This can be brought out as an equation.

Response: Thank you for the suggestion. In the revised manuscript, we have now explicitly presented this expression as a formal equation to enhance clarity and readability. The updated content can be found at Line 308.

Q12. Suggestions from reviewer: Table 2: My interpretation of the table is that DN1 corresponds to Band 2. DN typically represents the digital number within a band these formula can be readily misinterpreted. My suggestion is replace DN with Band2(DN) etc to clarify the band that is being used in the equation. Also add reference to F3, F4, F6, into the table either in the caption or as a legend to the table.

Response: Thank you for your valuable suggestion. While we did not revise the notation to express DN as Band2(DN) explicitly, we revised the main text to provide a more detailed explanation of "DN" and its association with specific spectral bands. Regarding F3, F4, and F6, we did not explain them individually; however, we clarified the overall meaning and role of F (fractional abundance) in the spectral unmixing model. We believe this improved contextual description effectively addresses potential confusion. Please refer to Lines 296–312 for the revised text.

Q13. Suggestions from reviewer: Section 4.2: Really should be in the geology section. The reference to the USGS spectral library should be in the methods section if used for spectral mapping.

Response: Thank you for your valuable suggestion. In response, we have revised the manuscript accordingly. The relevant content has been relocated from the original Section 4.2 to Section 2.3 "Overview of Remote Sensing Data" (Lines 170–188) to reflect its methodological nature. The use of the USGS spectral library for spectral mapping has also been clarified and appropriately referenced in this section to ensure consistency with the study's methodological framework.

Q14. Suggestions from reviewer: Line 290: This is not properly referenced. Since the USGS spectral library is used, it needs to be properly referenced.

Response: Thank you for your helpful comment. We have revised the manuscript to cite the USGS spectral library properly. The revised version has added the corrected reference (see Lines 184–188).

Q15. Suggestions from reviewer: Figure 7: Highlight the Fe, OH^-, CO₃²⁻, groups on the plots. This show the regions of interest in the spectral features.

Response: Thank you for your constructive suggestion. In response to your comment, we have revised Figure 7 to highlight the key absorption features corresponding to Fe³⁺, OH⁻, and CO₃²⁻ groups. These markers have been added directly to the spectral plots to clearly indicate the regions of interest, thereby improving the interpretability of diagnostic spectral features associated with iron-stained, Al–OH, Mg–OH, and carbonate alteration minerals. The updated figure can be found in the revised manuscript, as shown in Figure 7.

Q16. Suggestions from reviewer: Lines 298-300: This needs clarification that PCA was conducted on a subset of the 9 bands, to 4 bands, Band 2, 4, 8A, and 11 also explaining the subletting for the other channels as well. This is not clear.

Response: Thank you for your insightful comment. We have revised the manuscript to clarify that Principal Component Analysis (PCA) was performed on a subset of four Sentinel-2 bands (Band 2, Band 4, Band 8A, and Band 11) specifically for extracting iron-stained alteration anomalies. The rationale for selecting these bands has also been explicitly stated based on their spectral absorption and reflection characteristics. These revisions are reflected in Lines 328–339 of the updated manuscript.

Q17. Suggestions from reviewer: Lines 342-347: Create a table with the mean and standard deviation and mean + N*Sigma for each image. This will document the words provided.

Response: Thank you for your constructive suggestion. In response, we have created Table 4 titled "Statistical summary of alteration anomaly values for different alteration types in the Saga area", which includes the mean, standard deviation, and mean ± N×σ values for each type of alteration anomaly image. This addition provides a quantitative basis for the threshold selection described in the text and enhances the reproducibility and clarity of the methodology. Please refer to Table 4 in the revised manuscript.

Q18. Suggestions from reviewer: Figure 8: Line 349: place the (a), (b), etc prior to the mention. For example, (a) Iron-stained.

Response: Thank you for your suggestion. In the revised manuscript, we have adjusted the labeling format in the figure caption to place the subfigure indicators (a), (b), etc. before the corresponding descriptions—for example, "(a) Iron-stained" instead of "Iron-stained (a)." The revised caption can be found at Line 378.

Q19. Suggestions from reviewer: Figure 10:Line 391: See recommendation for Line 349

Response: Thank you for your comment. As recommended, we have revised the caption for Figure 10 to follow the same format used in Figure 8. The updated caption is shown at Line 420.

Q20. Suggestions from reviewer: Lines 398-400: This description of the units and their mineralogy should reside in the geology section.

Response: Thank you for your suggestion. In response, we have removed the description of lithological units and their associated mineralogy from this section and appropriately incorporated it into the revised geological background.

Q21. Suggestions from reviewer: Figure 11 (Line 432). It would be nice to see a partial transparency of Figure 2 underlain on this figure. If not underlain, a side by side of the geology map (Figure 2) with the result (Figure 11).

Response: Thank you for your valuable suggestion. In response, we have revised Figure 11 to include the geological map (originally Figure 2) as a partially transparent underlay beneath the alteration anomaly results. The revised figure is presented at Line 462 of the manuscript.

Q22. Suggestions from reviewer: Line 435: Plot the traverse on figure 11.

Response: Thank you for your suggestion. The field verification points are distributed within a relatively small area of the identified mineralization potential zones. Due to the limited spatial extent and the high density of information already present in Figure 11, adding the verification points directly on the map may compromise the overall clarity and readability of the figure. Therefore, we have chosen not to mark these points separately in the current version to maintain the figure's visual effectiveness.

Q23. Suggestions from reviewer: Figure 12: Describe if these photomicrographs are microscope, hand sample, reflected light, SEM and/or EPMA images.

Response: Thank you for your valuable comment. We have revised the manuscript to clarify the observation methods used for the photomicrographs shown in Figure 12. Specifically, we have added detailed descriptions in the figure caption and corresponding text (Lines 464–498) to indicate the imaging techniques employed. Figure 12c was obtained using cross-polarized light from a thin section under a transmitted light microscope, while Figures 12d–f were captured using reflected light under cross-polarized conditions. The other images (Figures 12a and 12b) are hand specimen photographs taken under natural light. No SEM or EPMA methods were used.

We have also re-examined the full text, and where errors were made in the review, we have reworked them accordingly. We would love to thank you for allowing us to resubmit a revised copy of the manuscript, and we highly appreciate your time and consideration. We also hope that the revised article will meet your expectations.

Thank you and best regards.

Sincerely.

Kai Qiao

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The research question in the introduction is not clearly stated. Please revise this section to explicitly define the research question and emphasize the significance of your study.

Please include a proper citation for the ENVI software mentioned in lines 145–146.

The method used to determine the composition of the measured region is unclear. Please clarify the procedure to ensure it is evident how the data presented in Figure 7 was obtained.

In the laboratory analysis section, please specify which types of characterizations were conducted to validate the remote sensing results.

Author Response

Dear reviewer

Re: Manuscript ID: minerals-3716081

Thank you for your comments concerning our manuscript entitled "Extraction of Remote Sensing Alteration Information Based on Integrated Spectral Mixture Analysis and Fractal Analysis". Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. Based on the instructions provided in your letter, we uploaded the revised manuscript file. Revisions in the text are shown using a red highlight for additions and a strikethrough font for deletions. The responses to the reviewer's comments are marked in red and presented as follows.

In the following, I will respond to each of the suggestions and questions raised by the reviewers.

Q1. Suggestions from reviewer: The research question in the introduction is not clearly stated. Please revise this section to explicitly define the research question and emphasize the significance of your study.

Response: Thank you for your constructive feedback regarding the clarity of the research question in the introduction. In the revised manuscript (Lines 100–118), we have explicitly defined the central research question as follows: "How can remote sensing techniques be effectively applied to identify and extract mineralization-related alteration anomalies in high-altitude, geologically complex regions such as the Saga area of Tibet, where field-based geological investigations are limited?" We also elaborated on the scientific significance of this study by emphasizing the challenges of traditional geological mapping in the Saga region due to its remote and rugged terrain. The introduction now clearly outlines the rationale for adopting a remote sensing–based approach and highlights the value of the proposed methodology for mineral exploration in inaccessible or extreme environments.

Q2. Suggestions from reviewer: Please include a proper citation for the ENVI software mentioned in lines 145–146.

Response: Thank you for your suggestion. In the revised manuscript (Lines 162–163), we have included a proper citation for the ENVI software used in the study as follows. We appreciate the reviewer's attention to citation accuracy.

Q3. Suggestions from reviewer: The method used to determine the composition of the measured region is unclear. Please clarify the procedure to ensure it is evident how the data presented in Figure 7 was obtained.

Response: Thank you for your comment. We have revised and relocated the relevant description to Section 2.3 "Overview of Remote Sensing Data" (Lines 170–188), where we clarified the procedure used to determine the spectral composition of the measured region. The method now explicitly explains the data source (USGS spectral library), the diagnostic absorption feature analysis, and how the representative spectra for different alteration types in Figure 4 (Original Figure 7) were obtained.

Q4. Suggestions from reviewer: In the laboratory analysis section, please specify which types of characterizations were conducted to validate the remote sensing results.

Response: Thank you for your valuable suggestion. We have revised and supplemented the laboratory analysis section (Lines 463–498) to specify the characterization methods used to validate the remote sensing results. Specifically, we describe the use of thin-section petrography under both transmitted and reflected light microscopy to analyze mineral assemblages and alteration types observed in the field. These analyses confirm the presence of mineralization consistent with the remotely sensed anomalies.

We have also re-examined the full text, and where errors were made in the review, we have reworked them accordingly. We would love to thank you for allowing us to resubmit a revised copy of the manuscript, and we highly appreciate your time and consideration. We also hope that the revised article will meet your expectations.

Thank you and best regards.

Sincerely.

Kai Qiao

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

This paper can be published.

Author Response

Dear Reviewer,

We sincerely thank you for your positive evaluation of our manuscript and for recommending its acceptance. We greatly appreciate your careful review and support, which have been very encouraging for our research.

With best regards,
Sincerely,