Optical Characterization of Coastal Waters with Atmospheric Correction Errors: Insights from SGLI and AERONET-OC

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for submitting such a clear and concise manuscript. I only have a few minor comments.

The description of the atmospheric correction algorithm that is applied to the SGLI data should be in the Methods instead of the Discussion (paragraph beginning on line 364).   

Volumes of riverine inflow should be expressed in cubic meters rather than tons.

Comments on the Quality of English Language

The English is perfectly clear. Grammatically, I would not start a paragraph with the word 'Similarly' (Line 306) as a paragraph should be a stand alone section of text, but that is pretty minor.  

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "Optical Characterization of Coastal Waters with Atmospheric Correction Errors: Insights from SGLI and AERONET-OC" presents a comprehensive study aimed at understanding the factors contributing to negative normalized water-leaving radiance (nLw(λ)) values in satellite observations from the Second-generation Global Imager (SGLI) sensor aboard the Global Change Observation Mission-Climate (GCOM-C) satellite. The research utilizes SGLI Level-2 data in conjunction with atmospheric and in-water optical properties measured by the sun photometers in AErosol RObotic NETwork-Ocean Color (AERONET-OC) from multiple sites globally, with a particular focus on Tokyo Bay and Ariake Sea.

The study's approach is methodologically sound, leveraging the robust AERONET-OC network for validation and comparison, which strengthens the reliability of the findings. The manuscript is well-organized, and the use of the Quasi-Analytical Algorithm version 5 (QAA_v5) for inherent optical properties (IOPs) estimation is appropriate for the research objectives.

However, there are several areas where the discussion could be enhanced, especially regarding the atmospheric correction for aerosol absorption:

1. Depth in Analysis of Aerosol Impact: While the manuscript identifies the influence of absorptive aerosols on the atmospheric correction process, the discussion could delve deeper into the specific types of aerosols present in the study areas and how they vary seasonally or due to anthropogenic activities. A more nuanced understanding of aerosol composition and its variability could provide insights into the reliability of the atmospheric correction models under different conditions.

2. Implications for Remote Sensing: The implications of the findings for remote sensing applications should be expanded upon. For instance, how do these findings affect the interpretation of long-term ocean color data sets used for climate studies? Discussing the broader applications and limitations of the study's conclusions would be beneficial.

4. Recommendations for Future Research: The manuscript could provide more concrete recommendations for future research. For example, suggesting the development of new algorithms or models that account for the specific optical properties of the study areas, or calling for further investigation into the role of aerosol absorption across different coastal environments.

3. Incorporate Machine Learning Approaches: Given the complexity of aerosol interactions and their impact on atmospheric correction, the discussion could consider the potential of machine learning techniques to improve the prediction of aerosol effects and enhance the accuracy of atmospheric correction models.

4. Uncertainty Quantification: While the study acknowledges the uncertainties in the atmospheric correction process, a more detailed analysis of these uncertainties and their propagation through the data could be provided. This could include a statistical assessment of the error margins and their impact on the study's conclusions.

In summary, the manuscript provides a solid foundation for understanding the challenges of atmospheric correction in coastal waters. Enhancements in the discussion, particularly around the atmospheric correction for aerosol absorption, could further strengthen the impact of the research and its relevance to the broader scientific community.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study analyzes the normalized water-leaving radiance parameters nLw provided by the Second-generation Global Imager satellite sensor. It focuses on the coastal waters affected by anthropogenic pollution of water bodies and anthropogenic emissions of aerosols. The original intention of this study is significant. However, the study presented in this paper has severe logical issues. Firstly, two Japanese Seas stations were roughly selected for analysis without clarifying their distinct characteristics compared to the other 24 stations. In addition, the paper is full of logical issues. The meaning between sentences is not coherent. It isn't easy to understand what the authors want to express. I cannot recommend publishing this paper based on these two serious issues. Following are my specific comments.

(1) The primary purpose of this article is to analyze the optical characterization of coastal waters with atmospheric correction errors. This optical characterization is a general characteristic of coastal waters with atmospheric correction errors, and similar characteristics should exist in different sea areas worldwide. The conclusion of this study is mainly based on the analysis of two stations in the Japanese waters. So, the main conclusion and the primary purpose are not consistent.

(2) Also, the Abstract states that this study identifies the factors contributing to negative nLw, and the two sites in the Japan Seas are just typical examples. However, the conclusion states that these two stations are the focus of the research.

(3) "First, we confirm the occurrence of atmospheric correction errors (Line 105)". Why must you first confirm that these two stations have this issue? Shouldn't you first analyze all the stations and confirm which of the 26 stations have this problem and which don't?

(4) Do any of the other 24 stations (excluding Tokyo Bay and Ariake Sea) also have the situation of "having an influx of anthropogenic aerosols and a high concentration of substances (Line 107)"? This paper explicitly selects two stations for analysis, which is logically problematic because it cannot be confirmed that they have distinct characteristics that differ from the other 24 stations. At least, the authors did not explain this point. The two stations were forcibly selected rather than being thoroughly compared and screened.

(5) These two sites, Tokyo Bay and Ariake Sea, appear for the first time in the text in the last paragraph of the Introduction in a very abrupt sense. Readers cannot understand why you must prioritize analyzing them.

(6) Figure 2 should show the results of all 26 stations and explain the significant differences between Tokyo Bay and Ariake Sea stations and the other 24 stations.

(7) Section 2.1 states that the target sea areas are two stations in Japan. The Abstract does not state that this study was conducted specifically for these two sites, but rather that it just has a particular focus on these two sites. Line 102 states that this study aims to analyze the factors that cause negative nLw values. These statements are contradictory to each other.

(8) Line 38: "… shows that high absorption coefficients, particularly of phytoplankton and colored dissolved organic matter …" It emphasizes that the two sites' high absorption coefficients are due to the phytoplankton and CDOM released near the coast. However, the following two sentences claim that the nLw is influenced by aerosol absorption. My query is how water pollution is linked to atmospheric absorption.

(9) Read only the Abstract; it is also difficult for readers to understand why you particularly focus on Tokyo Bay and the Ariake Sea.

(10) Line 34: What variable does "a significant decrease" here refer to? Or are you referring to the decrease in blue band regions relative to other (still not clear which) regions?

(11) Lines 36 and 39: What do "these negative values" mean? There is no mention of any "negative values" in the previous text

(12) Line 36: Why "443 nm" is chosen here rather than any other wavelengths is unclear. Why this wavelength value is unique?

(13) Line 39: Which five sites do you mean here? The previous text mentioned 26 sites globally, and you are particularly interested in two sites, Tokyo Bay and Ariake Sea. It is unclear which five sites are different and why they differ from others.

(14) Which regions do "these regions" refer to in the last sentence of the Abstract? Do you mean the blue band regions? It seems not.

(15) "Using SGLI Level-2 data, along with atmospheric and in-water optical properties measured by the sun photometers in AErosol RObotic NETwork-Ocean Color (AERONET-OC) from 26 sites globally." is a grammatical error sentence.

(16) Chlorophyll is an essential variable in this paper because it is related to the optical properties of the water, as well as factors such as nearshore human pollution and the abundance of nutrients in the water. These factors are also an essential basis for selecting two stations in Japan as typical examples. However, neither the Abstract nor the Introduction of this paper mention chlorophyll.

(17) The terms "deeply" and "in-depth" in the Abstract have little meaning. What parts of your research are casual and not in-depth enough?

(18) The sites in Table 1 should be numbered and indicated in Figure 1

(19) In Lines 164 to 174, the bold fonts in the text do not match the fonts in the formula.

(20) Figure 4 needs to explain the missing periods for observations.

Comments on the Quality of English Language

There are logical confusions among the sentences and paragraphs, seriously affecting readers' understanding.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1) This paper is valuable to those readers who want to do color sensing in Case-II waters and ultilize the AERONET data to validate the algorithms or data products.

2）Coastal Bays are mostly Case-II waters and one of the key issues of Case-II water color sensing is the method or algorithms of  atmospheric correction， which depends on sites or the optical properties of the waters. In my knowledge，many scientists and researchers have proposed various algorihtms to overcome this issue for turbid Case-II water and absorptive aerosol over past 30 years, but this paper, in the introduction section, lacks a even minimum concise and brief review for the classic papers or works or results. It is strongly recommended that to make a further  improvement in introduction. 

3) This paper, have not present enough material of the SGLI calibrations, the details of the algorithm of Case-II atmosphetic corection for the bays concerned, as well as the screening techniques to derive a reliable match-up data set from AERONET and their error bars estimated,  to enable readers to judge about if the "factors" considered in this paper are complete or enough.

4) About the "factors"  that contribute to the negtive nLwn values in blue bands, are definitely not well given in this paper, it need some more systematic way to analysis and explain, so that to support the conclusions of this paper. 

5) There is miss useage of OLCI for SGLI in last paragraph of Introduction.  

Comments on the Quality of English Language

English Language is good, much better than me!

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have carefully revised the paper and answered most of my raised issues. Meanwhile, before the paper can be published, I believe it must become more apparent in expressing viewpoints and conclusions.

For example, the Abstract claims that "this study identifies the factors contributing …" at the beginning; however, the following whole Abstract does not point out the "factors" obtained by the study. I have tried to tell through the Abstract what "factors" are and how they affect the nLw, but it's hard to find them. I believe that other average readers will also find it difficult.

For another example, the statements in Lines 602-620 are unclear in the Conclusion section. I have tried to find some of your contribution points based on the content of the Conclusion. However, it's also quite difficult for me to tell them. It is necessary to divide the section into several paragraphs to summarize several points of your conclusions.

Please revise the expression of the whole paper comprehensively, enhance readability, and pay special attention to the logical coherence among statements. It is essential for the average readers who are not explicitly focused on your field to understand your work.

Comments on the Quality of English Language

Revise the expression of the whole paper comprehensively, enhance readability, and pay special attention to the logical coherence among statements.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. This version has been greatly improved.

2. Althoug some other methods of atmospheric correction for case-II waters are still missing in the introduction section, it is fine for a  short paper.

      

Author Response

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Author Response File: Author Response.pdf