Calibration of Sentinel-2 Surface Reflectance for Water Quality Modelling in Binh Dinh’s Coastal Zone of Vietnam

Round 1

Reviewer 1 Report

The content is well described and contextualized with respect to the previous and present theoretical background and empirical research on the topic"Calibration of Sentinel-2 Surface Reflectance for Seawater Quality Modelling in Binh Dinh’s Coastal Zone of Vietnam".and for remote sensing research the results clearly presented and controlled. also, the results (especially tables 2,3, and Figures 3,5, and 5) show valid accordance with data and tools, and Working procedures were checked to find compliance, which seems appropriate.
Therefore, the present manuscript can be accepted in the same format.

Author Response

Comments and Suggestions for Authors

The content is well described and contextualized with respect to the previous and present theoretical background and empirical research on the topic"Calibration of Sentinel-2 Surface Reflectance for Seawater Quality Modelling in Binh Dinh’s Coastal Zone of Vietnam".and for remote sensing research the results clearly presented and controlled. also, the results (especially tables 2,3, and Figures 3,5, and 5) show valid accordance with data and tools, and Working procedures were checked to find compliance, which seems appropriate.
Therefore, the present manuscript can be accepted in the same format.

Response to reviewer 1:

Thank you very much for your valuable work on our submission. Many thanks for your read and check thoroughly entire the paper. We are much appreciated.

Reviewer 2 Report

1. In abstract section authors only presented the quantitative results it would be better if authors could add some qualitative results.

2. In abstract section line 33 to line 35, on the basis of which analysis authors have drawn this conclusion?

3. In section 2.1 the authors should add few details to justify the selection of study area. 

4. Authors should add some details regarding the processing and selection of the remote sensing data sets.

5. Abbreviations must be explained at first use and authors can revise the flowchart of their methodology as presented in the Figure 2 some unnecessary details are included in present figure.

6. The authors should add references for equations 1 to 6 as these are adopted from literature. 

7. The quality of Figure 3 should be improved it is difficult to read in present form.

 

6.

Author Response

Comments and Suggestions for Authors

Response to reviewer 2:

Thank you very much for your valuable work on our submission! That is really helpful for improving our paper. We are much appreciated for that.

1. In abstract section authors only presented the quantitative results it would be better if authors could add some qualitative results.

Response 1: We added a statement mentioning the qualitative results “In terms of seawater quality estimation, this accuracy is at a good level.”

2. In abstract section line 33 to line 35, on the basis of which analysis authors have drawn this conclusion?

Response 2: Thanks for your question? This conclusion is based on literature review in the introduction from the importance of coastal water, problems e.g. and we think this is not just for regions of Vietnam but for many coastal water in the world. We are sorry that in the abstract, citations are not recommended making this conlusion is not supported by references.

3. In section 2.1 the authors should add a few details to justify the selection of the study area. 

Response 3: Thank you for your suggestion. We add some information stating our reason for choosing this study area (at the end of the study area description).

4. Authors should add some details regarding the processing and selection of the remote sensing data sets.

Response 4: This is a good point to mention too, thanks. We added some information on remote sensing data processing and selection (lines 229-230) and line 278 (working flow section).

5. Abbreviations must be explained at first use and authors can revise the flowchart of their methodology as presented in Figure 2 some unnecessary details are included in the present figure.

Response 5: Thank you so much, we revised Fig.5 removing duplicates and making it a better presence.

6. The authors should add references for equations 1 to 6 as these are adopted from the literature. 

Response 6: we added references for equations 1 to 6.

7. The quality of Figure 3 should be improved it is difficult to read in its present form.

Response 7. We improved the Fig.3,4, and 5 qualities by making their labels larger.

Reviewer 3 Report

This study brings an important scientific contribution according to the scope of Sustainability. The study used a robust database of water quality data collected at 147 stations to assess the quality of seawater near the coast of Vietnam over 134 km. The authors calibrated the surface reflectance recorded by the MSI sensor aboard the Sentinel 2 satellites from in situ seawater surface reflectance data, allowing for the elimination of possible atmospheric interferences. In this way, the authors built a very consistent methodology to apply machine learning models. These models were used to quantify spatial water quality along the coast of Vietnam. This paper can be accepted after the authors revise some minor punctuation and referencing errors.

Author Response

This study brings an important scientific contribution according to the scope of Sustainability. The study used a robust database of water quality data collected at 147 stations to assess the quality of seawater near the coast of Vietnam over 134 km. The authors calibrated the surface reflectance recorded by the MSI sensor aboard the Sentinel 2 satellites from in situ seawater surface reflectance data, allowing for the elimination of possible atmospheric interferences. In this way, the authors built a very consistent methodology to apply machine learning models. These models were used to quantify spatial water quality along the coast of Vietnam. This paper can be accepted after the authors revise some minor punctuation and referencing errors.

Response to Reviewer 3:  Thank you so much for your review of our paper. We are so thankful for your compliments, which encourage us a lot. We revised the paper carefully, and all punctuation and referencing errors are double-checked and solved. The paper is edited by Dr. Greg Nagle who is a US native speaker and majored in the same field as this paper.

Reviewer 4 Report

Thank you for submitting your manuscript to the Sustainability journal. Generally, the topic fits into the scope of the journal, and the structure respects Scientific Best Practice. In the literature review, it is important that the scientific novelty of the work is established through a critical analysis of related literature. With this, followng questions must be clarified: How does the present work contribute towards the gaps identified? How does it improve upon previous work? It is recommended that a short discussion of the novel contribution of each reference cited shall be provided to give readers a better understanding of their relevance. Thus, the main questions of the reviewer are: What is the scientific motivation for the study? What is your scientific hypothesis that you wish to answer
with the inbestigation? Putting the scientific motivation will also help
you to identify the novelties that characterises a scientific publication.

Moreover, section 1.1 is much too long with a lot of not necessary text and
needs to be shortened. Section 1.2 is generelly ok, however, the state of
the art in terms of machine learning methods is missing.

In the Methology section, it remains unclear how the authors reach from spectral
data to water quality concentrations. This subject must be explained more in
detail.

Moreover, the reviewer wants to know why you focused on the mentioned parameters,
and they do not include metals, particularly as in the coastal regions of
the Binh Dinh province, there are a lot of titanium mining sites at the
beaches that might impact the quality of the sea water.

In the results section, it should be explained where was set the border of
the investigation area in direction of the marine envieonment, and why. In the conclusions, in addition to summarising the actions taken and results, please strengthen the explanation of their significance. It is recommended to use quantitative reasoning comparing with appropriate benchmarks, especially those stemming from previous work.  

 

Author Response

Thank you for submitting your manuscript to the Sustainability journal. Generally, the topic fits into the scope of the journal, and the structure respects Scientific Best Practice. In the literature review, it is important that the scientific novelty of the work is established through a critical analysis of related literature. With this, following questions must be clarified: How does the present work contribute towards the gaps identified? How does it improve upon previous work? It is recommended that a short discussion of the novel contribution of each reference cited shall be provided to give readers a better understanding of their relevance. Thus, the main questions of the reviewer are: What is the scientific motivation for the study? What is your scientific hypothesis that you wish to answer
with the investigation? Putting the scientific motivation will also help
you to identify the novelties that characterises a scientific publication.

The general response to reviewer 4: Thank you very much for your comments and suggestions for our paper. That are really helpful for improving the paper quality. We addressed your questions one by one as follows:

How does the present work contribute towards the gaps identified? How does it improve upon previous work? 

Response: We added a statement and a short paragraph addressing these points (lines 133-143) and 176-181 in section 1.2 of the introduction.

It is recommended that a short discussion of the novel contribution of each reference cited shall be provided to give readers a better understanding of their relevance:

Response: We added a short discussion in the result and discussion section (3.4 line 524-527) with 3 references.

What is the scientific motivation for the study? What is your scientific hypothesis that you wish to answer with the investigation?

Response: This point is also addressed in the added short paragraph line 176-181 in section 1.2 of the introduction.

1. Moreover, section 1.1 is much too long with a lot of not necessary text, and
needs to be shortened. Section 1.2 is generally ok, however, the state of
the art in terms of machine learning methods is missing.

Response 1: Thank you very much for your suggestion. We shortened section 1.1 and deleting text is not really necessary. We added a statement mentioning the state of the art of machine learning methods in lines 152-153.

2. In the Methodology section, it remains unclear how the authors reach from spectral
data to water quality concentrations. This subject must be explained more in
detail.

Response 2: We added two sentences to explain this point at the beginning of section 2.3 (2.3. Flow-work of methodology)

3. Moreover, the reviewer wants to know why you focused on the mentioned parameters,
and they do not include metals, particularly in the coastal regions of
the Binh Dinh province, there are a lot of titanium mining sites at the
beaches that might impact the quality of the seawater.

Response 3 (explanation): We choosing water quality parameters based on the ability to extract from remote sensing data (here is Sentinel-2) through review literature (based on a google scholar search; there are 40,000 articles (chla), 17,000 (TSS, COD) and a much lower number mentioned DO use remote sensing data. As we mentioned in the introduction, there are hundreds of water quality parameters but not all of them can be extracted from remote sensing (no correlation or very little). You are absolutely right that in Binh Dinh province, there are a lot of metals, and titanium mining sites at the beaches that might impact the quality of the seawater. We would like to investigate these parameters using remote sensing, but direct measurements could be a more appropriate approach.

4. In the results section, it should be explained where was set the border of
the investigation area in direction of the marine environment, and why.

Response 4. Thank you so much for your suggestions: We added some explanation about the investigation area in the result section 3.6 (lines 468-472).

5. In the conclusions, in addition to summarising the actions taken and results, please strengthen the explanation of their significance. It is recommended to use quantitative reasoning compared with appropriate benchmarks, especially those stemming from previous work.  

 Response 5. Thank you for your good suggestion. We added a comparison with appropriate benchmarks (national coastal water quality standards with references) explanation of their significance and actions in the conclusion (lines 503-506).