Inland Water Quality Monitoring Using Airborne Small Cameras: Enhancing Suspended Sediment Retrieval and Mitigating Sun Glint Effects

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript explores the use of multispectral and hyperspectral UAV platforms for monitoring Total Suspended Solids (TSS) in inland waters, addressing critical challenges such as sun glint effects and radiometric accuracy. While the study demonstrates a comprehensive approach and provides valuable insights, it requires significant revisions to improve clarity, depth, and scientific rigor. The introduction and abstract should be streamlined to highlight the research’s novelty, while the methodology needs a clearer explanation of data quality control and error handling. The results section, although rich in content, often lacks in-depth analysis and connection to existing literature, particularly concerning spectral correlations and correction methods. The conclusions should better emphasize the study’s contributions and provide actionable recommendations. With these improvements, the paper could make a substantial contribution to UAV-based water quality monitoring research.

 

 

specific comments:

Abstract 

The abstract is too long, contains redundant information, and lacks clear structure. 

Introduction

Lines 44–49: The description of TSS’s definition and importance is repetitive.

Lines 51–62: The limitations of satellite remote sensing are scattered.L

ines 70–90): While UAV advantages are mentioned, limitations are not explored in detail.

 

Results and Discussion

Lines 307–329: The discussion of image stitching failures is limited to describing the phenomenon.

Lines 375–438: While sun glint effects and correction methods are discussed, a comparison of their applicability is missing.

Lines 473–521: The discussion on TSS concentration and spectral correlation focuses on the NIR region but overlooks variations at low or high concentrations.

Lines 561–583: The TSS maps related to the Brumadinho disaster lack sufficient explanation.

Conclusion 

Lines 596–609: The conclusions are too general and fail to highlight the core contributions of the study.

Lines 610–646: The recommendations for UAV platforms are insufficiently supported.

Formatting and Language

Lines 183–204 and 564–573: The figure captions are too brief and require more detailed annotations.

Comments on the Quality of English Language

No

Author Response

Revisor 1

 

The manuscript explores the use of multispectral and hyperspectral UAV platforms for monitoring Total Suspended Solids (TSS) in inland waters, addressing critical challenges such as sun glint effects and radiometric accuracy. While the study demonstrates a comprehensive approach and provides valuable insights, it requires significant revisions to improve clarity, depth, and scientific rigor. The introduction and abstract should be streamlined to highlight the research’s novelty, while the methodology needs a clearer explanation of data quality control and error handling. The results section, although rich in content, often lacks in-depth analysis and connection to existing literature, particularly concerning spectral correlations and correction methods. The conclusions should better emphasize the study’s contributions and provide actionable recommendations. With these improvements, the paper could make a substantial contribution to UAV-based water quality monitoring research.

R: A more detailed explanation of data quality control and error handling has been provided. Additionally, statistical metrics for evaluating the results have been included in Section 2.4, along with expanded paragraphs clarifying the methodology.

             

specific comments:

Abstract 

The abstract is too long, contains redundant information, and lacks clear structure. 

R: Thank you for the observation. We noticed the redundant information in the summary and have made the necessary adjustments to eliminate it. We believe the revised text is now clearer and more concise.

 

Introduction

Lines 44–49: The description of TSS’s definition and importance is repetitive.

R: We have also made adjustments to remove redundancies, and we now believe the text is clearer and more concise.

 

 

 

Lines 51–62: The limitations of satellite remote sensing are scattered.

R: The paragraph has been revised to present the limitations in a more structured and cohesive manner.

 

Lines 70–90): While UAV advantages are mentioned, limitations are not explored in detail.

R: The penultimate paragraph of the introduction focuses entirely on the limitations of UAVs, particularly regarding water quality monitoring. Minor adjustments were made to enhance its clarity.

 

Results and Discussion

Lines 307–329: The discussion of image stitching failures is limited to describing the phenomenon.

R: Four additional lines have been included in the paragraph to provide a more detailed description of the phenomenon.

 

Lines 375–438: While sun glint effects and correction methods are discussed, a comparison of their applicability is missing.

R: A new paragraph has been added to the topic (last paragraph in topic 3.2) to compare its applicability and discuss various sun glint correction methodologies available in the literature.

 

Lines 473–521: The discussion on TSS concentration and spectral correlation focuses on the NIR region but overlooks variations at low or high concentrations.

R: The last paragraph of Section 3.3 is entirely dedicated to discussing the limitations of NIR at both high and low TSS concentrations.

 

Lines 561–583: The TSS maps related to the Brumadinho disaster lack sufficient explanation.

R: A new paragraph has been added to the topic (After Figure 14) to provide additional explanation and enhance clarity.

 

Conclusion 

Lines 596–609: The conclusions are too general and fail to highlight the core contributions of the study.

R: Three new paragraphs have been added at the beginning of the conclusion to better highlight the study's contributions.

 

Lines 610–646: The recommendations for UAV platforms are insufficiently supported.

R: The article does not have a specific section dedicated to UAV types, specifications, and their advantages and disadvantages. While such a section could be included, the work is already quite lengthy. The information on UAVs presented in the conclusion is somewhat general or widely discussed in the literature:

• Multirotor UAV: Offers greater stability but covers smaller areas. Ideal for small-scale applications.
• Fixed-wing UAV: Less stable but provides larger coverage. Suitable for extensive areas.
• VTOL UAV (Vertical Take-Off and Landing): Combines the advantages of both multirotor and fixed-wing UAVs, making it versatile but more expensive.

 

Formatting and Language

Lines 183–204 and 564–573: The figure captions are too brief and require more detailed annotations.

R: Details have been added to the figure legends

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript investigates the efficiency of UAV platforms in monitoring TSS. It emphasizes evaluating the influence of sun glint on image quality and examines the performance of various sensors in TSS monitoring. Its topic is appropriate for drones and the results of this study are very interesting. However, the manuscript is kind of hard to follow in the present format and should be much improved with regard to the limited analysis on the relationship between sun glint and TSS. Thus, I recommend a major revision of this MS.

 

1. In the results section, the authors devoted extensive discussion to the impact of sun glint on image quality but did not explore its relationship with TSS. Based on the article's title, it is clear that monitoring TSS is the ultimate goal of the authors. Therefore, it is recommended to include a comparative analysis of how sun glint affects UAV-based TSS monitoring.

2. The authors collected data from various types of water bodies and provided relevant recommendations in Section 4 of the manuscript. However, the discussion of this aspect is insufficient in Section 3 (Results and Discussion). It is recommended to enhance this discussion.

3. The introduction should be reorganized. The manuscript compares water bodies with different characteristics, but the introduction provides little information on this topic. It is recommended to expand this section to elaborate on the specific challenges faced in monitoring the water quality of inland water bodies, such as the complexity of water quality variations across different types of water bodies (e.g., lakes, rivers) and the limitations of existing monitoring technologies in addressing these challenges.

4. Line 116：Is "COAs" a spelling error?

5. The layout of Figure 1 appears cluttered, and its main focus is not clear.It is recommended to replace the photos showing the different water body types to enhance the contrast between A, B, C, and D.

6. Lines 270-272: It is recommended to briefly introduce the method for extracting TSS rather than simply citing references.In addition, the basic information of the measured TSS samples should be provided, such as the number and concentration range.

7. Lines 369-371: This sentence is unclear and needs revision.What does medium to high resolution satellite imagery refer to here, and what is the range of specific resolutions? What material is not suitable for monitoring in this area, referring to TSS?

Author Response

Revisor 2

 

The manuscript investigates the efficiency of UAV platforms in monitoring TSS. It emphasizes evaluating the influence of sun glint on image quality and examines the performance of various sensors in TSS monitoring. Its topic is appropriate for drones and the results of this study are very interesting. However, the manuscript is kind of hard to follow in the present format and should be much improved with regard to the limited analysis on the relationship between sun glint and TSS. Thus, I recommend a major revision of this MS.

 

1. In the results section, the authors devoted extensive discussion to the impact of sun glint on image quality but did not explore its relationship with TSS. Based on the article's title, it is clear that monitoring TSS is the ultimate goal of the authors. Therefore, it is recommended to include a comparative analysis of how sun glint affects UAV-based TSS monitoring.

R: The penultimate paragraph of the introduction includes a sentence addressing the challenges posed by the sun glint effect on remote sensing water quality monitoring in general. In this sentence, we have added emphasis on TSS. However, we believe it is not feasible to introduce or discuss the effect of sun glint specifically on TSS. Sun glint impacts all water components similarly, with no distinct effect or treatment related to TSS. When sun glint is present in an image, it will affect the monitoring of TSS as well as other optically active components. Correcting this effect will enhance the overall monitoring accuracy for all components. The accuracy of monitoring a specific component, such as TSS, will ultimately depend on the type of estimation model used.

 

2. The authors collected data from various types of water bodies and provided relevant recommendations in Section 4 of the manuscript. However, the discussion of this aspect is insufficient in Section 3 (Results and Discussion). It is recommended to enhance this discussion.

R: A new paragraph has been added to section 3.3 (below Figure 10) to enrich the discussion on the differences in types of water bodies. However, it is worth mentioning that the last paragraph of topic 3.3 is entirely dedicated to the differences in TSS monitoring on waters with low and high concentrations.

 

3. The introduction should be reorganized. The manuscript compares water bodies with different characteristics, but the introduction provides little information on this topic. It is recommended to expand this section to elaborate on the specific challenges faced in monitoring the water quality of inland water bodies, such as the complexity of water quality variations across different types of water bodies (e.g., lakes, rivers) and the limitations of existing monitoring technologies in addressing these challenges.

R: A new paragraph has been added to section 3.3 (below Figure 10) to enrich the discussion on the differences in types of water bodies. However, it is worth mentioning that the last paragraph of topic 3.3 is entirely dedicated to the differences in TSS monitoring on waters with low and high concentrations.

 

4. Line 116：Is "COAs" a spelling error?

R: Thank you very much for your comment. I apologize for the oversight in the translation. "COAs" is an abbreviation for "Componentes Opticamente Ativos" in Portuguese, and it has now been correctly translated as "OACs."

 

5. The layout of Figure 1 appears cluttered, and its main focus is not clear.It is recommended to replace the photos showing the different water body types to enhance the contrast between A, B, C, and D.

R: Figure 1 has been modified according to the reviewer’s suggestions. However, we believe that the previous version, presented as photos, was more instructive in highlighting the details of the areas and study.

 

6. Lines 270-272: It is recommended to briefly introduce the method for extracting TSS rather than simply citing references.In addition, the basic information of the measured TSS samples should be provided, such as the number and concentration range.

R: A new sentence has been added to the paragraph in question to provide a clearer explanation of the TSS extraction method. The basic TSS information is presented in Table 1.

 

7. Lines 369-371: This sentence is unclear and needs revision.What does medium to high resolution satellite imagery refer to here, and what is the range of specific resolutions? What material is not suitable for monitoring in this area, referring to TSS?

R: Adjustments have been made to the paragraph. The terms "high resolution" and "low resolution" were mistakenly confused, and the spatial resolution threshold for the specific case has now been clearly indicated.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript Title: Unmanned Aerial Imagery: A Methodological Review to Enhance Total Suspended Solids Monitoring in Inland Waters

 

This manuscript attempts to address the issue of sun glint in orthophotos captured by UAVs and explores the inversion of total suspended solids (TSS) in water bodies using multispectral and hyperspectral cameras. This is a meaningful effort, as the proposed workflow could potentially tackle practical challenges in fieldwork—particularly the issue of sun glint. However, despite the revisions made in the previous version, I believe the manuscript still has several shortcomings.

 

General Comments:

1. Title Ambiguity: The current title is ambiguous and does not clearly reflect the innovative aspects of the study. A more precise and focused title is recommended to better communicate the research scope.

2. Formatting Issues: The manuscript preparation appears rushed, as demonstrated by formatting errors in the abstract (e.g., lines 27 and 29). Consistency and attention to detail are essential for a professional presentation.

3. Structural Reorganization: The manuscript requires structural adjustments to emphasize its key contributions rather than simply trimming excessive content. The current structure disperses the focus, making it difficult to highlight the novelty of addressing sun glint—arguably one of the study’s most practical and innovative aspects.

4. Focus and Clarity: Excessive content, including some tangential or unrelated discussions, diminishes the manuscript’s clarity and impact. A streamlined narrative is necessary to make the research’s novelty more apparent and compelling.

5. Potential for Impact: The effort to address sun glint in UAV-based imagery is particularly promising and practical. By refining the narrative and prioritizing this aspect, the manuscript has the potential to become a significant contribution to the field.

 

Recommendations for Improvement:

1. Revise the title to explicitly reflect the study’s primary focus, such as mitigating sun glint in UAV imagery or improving TSS monitoring workflows.

2. Enhance manuscript quality by addressing formatting inconsistencies and ensuring the abstract succinctly communicates the study’s innovations.

3. Reorganize the structure to emphasize the main contributions, particularly the methodological advancements in addressing sun glint.

 

More specific comments update:

I would like to clarify that your questions essentially ask for guidance on how to revise or even write the manuscript. Strictly speaking, it is not the reviewer’s responsibility to provide such detailed instructions. Moreover, I personally feel that you have not thoroughly addressed the comments I provided in my previous review.

 

Here are my responses to your specific concerns:
1. *Title and Structure*:
The title is the soul of a paper. If the title requires modification, it necessitates corresponding adjustments to the content and structure, as the focus of the paper might modify. Simply tweaking the title without revising the content will inevitably lead to similar feedback in the next round of review.
2. *Purpose and Results*:
Based on the content of your manuscript, I believe the results (TSS concentrations) you have presented should not be the primary focus. The results are evidence supporting your proposed new methodology, not the ultimate objective of the study. The inversion of suspended particulate matter in water using UAVs has already been extensively validated in numerous studies, especially those involving satellite-based multispectral and hyperspectral applications. If you consider this aspect to be the main innovation, I am afraid the manuscript may not be suitable for publication.
However, if the paper’s focus shifts towards establishing a novel workflow or operational process, this could potentially become a meaningful contribution. Nevertheless, you must carefully consider how to validate your approach and provide robust evidence for its effectiveness.
3. *Focus on Sun Glint Removal*:
If your research emphasizes the removal of sun glint, I believe this would be particularly interesting and relevant. Sun glint is a significant challenge in UAV field operations, as it often limits data acquisition to specific times of day to avoid glare. Addressing this issue would make your study highly practical and valuable.
4. *Organizing the Manuscript*:
It is ultimately your responsibility as authors to refine the structure of the manuscript. You need to determine how best to present your innovations clearly and convincingly.

 

Based on the above, I suggest that you consider one of the following directions:
1. Focus on elaborating the operational workflow and highlight any innovative aspects.
2.Emphasize methods for mitigating sun glint and present this as the core contribution.

 

Both directions, in my opinion, have the potential to engage readers’ interest. However, the final decision lies with the editor, not me.

 

Finally, I regret that I cannot provide further detailed suggestions, as that would cross the line into writing the paper for you. I genuinely appreciate the opportunity to discuss this with you and hope my feedback will prove helpful.

Comments on the Quality of English Language

 The English could be improved to more clearly express the research.

Author Response

Dear Reviewer,

First and foremost, we sincerely appreciate your insightful comments and the reinforcement of key contributions that have undoubtedly helped to improve our manuscript. I would like to provide a general response, considering all the points raised.

We do not intend to convey the idea that TSS results are the primary focus of this article. This topic has already been extensively explored in the literature, both through satellite imagery and, more recently, via drones. An exclusive focus on TSS mapping, even when utilizing different drone platforms, would not be sufficient or appropriate for publication in Drones.

Our aim is to integrate a set of variables related to aerial water quality surveys as a whole. However, we have chosen to emphasize the TSS parameter based on our prior experience with this indicator. The integration of these variables, with the goal of providing recommendations for future applications, is what justifies the publication. While the study specifically addresses TSS, the proposed approach is also applicable to monitoring other water quality parameters using drones, particularly in aspects related to the construction of orthomosaics in homogeneous areas and the mitigation of sun glint effects. For these reasons, we consider all topics discussed in the results (and throughout the manuscript) to have equal relevance. The combination of these elements forms the foundation of our final considerations, where we recommend optimal platforms and methodologies for future studies. Once again, we emphasize that this integration of factors is the central focus of our article.

Although we have justified and assigned equal importance to all topics, including the integration of factors, we recognize and appreciate the Reviewer’s valuable observations regarding the innovative aspect of the topic on sun glint mitigation. In response to these suggestions, we have made adjustments throughout the manuscript to better highlight these contributions:

 

1. The title has been modified.
2. The abstract has been completely restructured.
3. The final paragraph of the introduction has been revised.
4. The title of Section 4 has been changed.
5. Section 4 has been reorganized, with the first paragraph now dedicated to sun glint.

 

These five changes have been made to further emphasize the methodologies for mitigating sun glint effects. In doing so, we have strived to fully address your valuable comments

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Agree with the author's current revision and recommend that it be accepted.

Author Response

Dear Reviewer,

We sincerely appreciate your thoughtful contributions, which have undoubtedly helped improve the manuscript.