The Influence of Anisotropic Surface Reflection on Earth’s Outgoing Shortwave Radiance in the Lunar Direction

Round 1

Reviewer 1 Report

The authors have revised the paper and clarified my comments. For me the paper is fine and can be accepted. However, I would consider also the comments from other reviewers, since I am not deeply familiar with the methods presented by the authors in the paper.

Reviewer 2 Report

Dear authors,

thanks for the updated version of the paper and for the detailed responses to my comments, I'm fine with the replies. I believe the paper has greatly improved and can be considered for publication in the present form.

I only have a final suggestion: improve the description of the figures, especially Fig. 14-16, the caption should be self-explaining, clearly describing what is plotted, the axis and the labels if the figure is splitted in several panels

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The paper describes the modelling of reflected Earth radiation toward the Moon in the short wavelength spectral range. Monitoring the Earth’s radiation budget is important because it is the main parameter in the global warming debate. In general, I have found the paper a bit difficult to read and some points need to be clarified.

• In the text, the authors consider the TOA reflection. As written, TOA reflection is due to air molecules at about 100 km altitude. However, in their study they consider also surface reflection. Please clarify this point.
• If the authors include surface reflection, why they do not include also clouds and aerosols in the model (they use only a cloud cover < 5%)? They say that clouds anisotropy is small as viewed from the Moon. But cloud coverage changes with time and location so from the Moon you have both poor spatial and temporal resolution, compared to a LEO satellite.
• The authors call shortwave radiation the spectral range from 0.3-5 micron. This spectral range is so wide that you have different scattering regimes, both molecular and Mie scattering. In equation 11 the anisotropic factors are a function of geometric angles alone, I do not understand why they are not a function of wavelength too.
• The authors found that the anisotropy has a maximum at the beginning and at the end of the lunar month. This was well expected since the surface is the main source of this anisotropy. Again, having excluded clouds and aerosols, this result is quite trivial.

The paper is too crowded of technical details and this makes difficult to follow the reasoning. I suggest to put the text from line 167 to 228 in Appendix B. Also table 3, which is not fundamental for the overall understanding, can be put in the appendix.  In general, the authors should improve the paper readability. The English is fine but often, it is not easy to follow the reasoning.

Figure 2 is misleading:

• There is an error in the figure, label B is not present (O instead)
• You call A sunlit region. It is better to call it “sunlit portion not visible from the Moon”

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

1. The manuscript presents the influence of anisotropic TOA reflection on earth’s out-going shortwave radiance in the lunar direction, which is interesting. The subject addressed is within the scope of the journal.
2. However, the manuscript, in its present form, contains several weaknesses. Appropriate revisions to the following points should be undertaken in order to justify recommendation for publication.
3. Full names should be shown for all abbreviations in their first occurrence in texts. For example, JPL in p.6,
4. For readers to quickly catch your contribution, it would be better to highlight major difficulties and challenges, and your original achievements to overcome them, in a clearer way in abstract and introduction.
5. It is shown in the reference list that the authors have several publications in this field. This raises some concerns regarding the potential overlap with their previous works. The authors should explicitly state the novel contribution of this work, the similarities and the differences of this work with their previous publications.
6. 1 - the influence of anisotropic TOA reflection is adopted as the focus of this study. What are other feasible alternatives? What are the advantages of adopting this approach over others in this case? How will this affect the results? The authors should provide more details on this.
7. 1 - three time-scales are adopted in the model. What are the other feasible alternatives? What are the advantages of adopting these time-scales over others in this case? How will this affect the results? More details should be furnished.
8. 3 - the integration of the variables of anisotropic TOA reflection and radiant flux in Moon-viewed sunlit regions is adopted as the primary method of the study. What are other feasible alternatives? What are the advantages of adopting this approach over others in this case? How will this affect the results? The authors should provide more details on this.
9. 4 - a model with flowchart as shown in Figure 1 is adopted to estimate Earth’s OSR in the lunar direction. What are other feasible alternatives? What are the advantages of adopting this framework over others in this case? How will this affect the results? The authors should provide more details on this.
10. 5 - transformation of reference systems as shown in Figure 3 is adopted to get geometrical parameters. What are other feasible alternatives? What are the advantages of adopting this approach over others in this case? How will this affect the results? The authors should provide more details on this.
11. 10 - only clear-sky conditions are adopted in this work. What are the other feasible alternatives? What are the advantages of adopting this approach over others in this case? How will this affect the results? More details should be furnished.
12. 13 - four random days in 2016 (leap year) and 2019(common year) are adopted as case examples. What are the other feasible alternatives? What are the advantages of adopting these case examples over others in this case? How will this affect the results? More details should be furnished.
13. 18 - “…As RAAs are close to 0°, the anisotropic factors of the “clear ocean” type are larger and maximum factors can reach 12. This is why.…” More justification should be furnished on this issue.
14. 18 - “…found no outliers like the dots framed in red rectangles, which are inversely proportional to RAA and proportional to area. We speculate this is caused by.…” More justification should be furnished on this issue.
15. 18 - “…After many numerical simulations, we concluded that, due to the large MsR and small MZAs, weight factors f in (a) and (c) are much smaller than in (b) and (d), resulting in.…” More justification should be furnished on this issue.
16. The discussion section in the present form is relatively weak and should be strengthened with more details and justifications.
17. Some key parameters are not mentioned. The rationale on the choice of the particular set of parameters should be explained with more details. Have the authors experimented with other sets of values? What are the sensitivities of these parameters on the results?
18. Some assumptions are stated in various sections. Justifications should be provided on these assumptions. Evaluation on how they will affect the results should be made.
19. Moreover, the manuscript could be substantially improved by relying and citing more on recent literatures about contemporary real-life applications of modelling in solar radiation such as the followings. Discussions about result comparison and/or incorporation of those concepts in your works are encouraged:

• Ebtehaj, I., et al., “Prognostication of Shortwave Radiation Using an Improved No-Tuned Fast Machine Learning,” Sustainability 13 (14): 8009 2021.
• Huang, L.X., et al., “Solar Radiation Prediction Using Different Machine Learning Algorithms and Implications for Extreme Climate Events,” Frontiers in Earth Science 9: 596860 2021.
• Beyaztas, U., et al., “Construction of Functional Data Analysis Modeling Strategy for Global Solar Radiation Prediction: Application of Cross-Station Paradigm,” Engineering Applications of Computational Fluid Mechanics 13 (1): 1165-1181 2019.
• Samadianfard, S., et al., “Daily global solar radiation modeling using data-driven techniques and empirical equations in a semi-arid climate,” Engineering Applications of Computational Fluid Mechanics 13 (1): 142-157 2019.

20. In the conclusion section, the limitations of this study, suggested improvements of this work and future directions should be highlighted.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Thanks for submitting your work, this is a good paper and a leap forward towards the exploitation of a Moon-based EO observing system.

The methods are scientifically sound and the results clearly presented. I've only rather minor comments attached to the review.

As far as these comments are addressed I would recommend publication of this paper in MDPI RS.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx