Compatibility Between OLCI Marine Remote-Sensing Reflectance from Sentinel-3A and -3B in European Waters

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

All the issues have been addressed and the current version can be accepted.

Author Response

Thanks a lot for taking the time to review our work. This is really appreciated.

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The author solved my problems, I don't have any more questions.

Author Response

Thanks a lot for taking the time to review our work. This is really appreciated.

Reviewer 3 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

Dear Authors,

The author has properly addressed my previous concerns and has significantly improved the quality of the manuscript. However, I believe that additional details could be provided in certain areas. Currently, the discussion primarily focuses on inter-instrument errors and uncertainties. The author may need to include some discussion on how the calculated uncertainties in remote sensing reflectance or any derived numerical differences might impact satellite ocean products.

In particular, ESA’s Copernicus Marine Service and NASA Ocean Color provide a wide variety of ocean color products derived from Sentinel-3A and -3B data, including chlorophyll concentration, water transparency, and extended ocean carbon products. Should these products be improved? Or how might they be affected by the reported uncertainties?

Additionally, it would be beneficial to include references to relevant key literature on remote sensing reflectance in the Introduction.

Author Response

Dear Reviewer,

Thanks for taking the time to review our work. Please find below responses to each set of comments.

Comments 1: The author has properly addressed my previous concerns and has significantly improved the quality of the manuscript. However, I believe that additional details could be provided in certain areas. Currently, the discussion primarily focuses on inter-instrument errors and uncertainties. The author may need to include some discussion on how the calculated uncertainties in remote sensing reflectance or any derived numerical differences might impact satellite ocean products.

In particular, ESA’s Copernicus Marine Service and NASA Ocean Color provide a wide variety of ocean color products derived from Sentinel-3A and -3B data, including chlorophyll concentration, water transparency, and extended ocean carbon products. Should these products be improved? Or how might they be affected by the reported uncertainties?

Response 1:

Thanks for the comments. It is true that the discussion mostly focuses on inter-instrument (and inter-camera) differences as this is the subject of the work. An analysis of how differences observed in RRS propagate to the numerous ocean-colour derived products is not straightforward (considering the diversity of products and of algorithms) and would require a dedicated study. But the topic is certainly relevant and a paragraph has been added in the Discussion section (lines 568-577) that briefly discusses this point:

“These conclusions, suggesting insufficient compatibility, have certainly an impact on derived products such as Chla as errors are propagated through bio-optical algorithms (IOCCG, 2019, McKinna et al. 2019). Uncertainties expressed in relative terms generally tend to increase for derived products but, without dedicated studies, it is challenging to conclude on their inter-mission compatibility based on the results obtained with RRS as the propagation of errors depends on the functional form of the associated algorithm. For instance, band-ratio and band-difference algorithms used for Chl-a behave differently when handling errors in RRS (Hu et al. 2012). Besides implications on pixel-based uncertainties, the potential cross-camera issues discussed in this work would also have a bearing on spatial analyses using ocean colour data, such as front detection (Druon et al. 2021), by introducing artifacts in the imagery.”

The issue of improvements of the Sentinel-3 ocean colour products is actually the 1^st recommendation given in the last paragraph of the paper.

 

Comments 2: Additionally, it would be beneficial to include references to relevant key literature on remote sensing reflectance in the Introduction.

Response 2: An additional paragraph (2^nd paragraph of the introduction) has been added (lines 38-44), giving more background on remote sensing reflectance with appropriate references.

Round 2

Reviewer 3 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

Dear Authors,

I agree with the additional explanations and references provided by the authors. I believe the manuscript is now acceptable for publication.

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

Comments and Suggestions for Authors

This manuscript is well-written, with a clear structure and detailed methodology that effectively evaluate the compatibility of Sentinel-3A and Sentinel-3B OLCI marine remote sensing reflectance data. This paper represents contribution to the field of ocean color remote sensing, particularly in its detailed examination of Sentinel-3A and Sentinel-3B compatibility. The study sets a strong foundation for further research on long-term ocean color data integration and climate monitoring applications.  There are a few minor issues listed in the attachment for the author to consider

Comments for author File: Comments.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Review for “Compatibility between OLCI marine remote sensing reflectance from Sentinel-3A and -3B in European waters”

 

This paper examines the compatibility of remote sensing reflectance (RRS) data derived from the Ocean and Land Colour Imager (OLCI) onboard the Sentinel-3A and Sentinel-3B satellites over European waters. The authors validate the data using field measurements from the Aerosol Robotic Network Ocean Color (AERONET-OC) and analyze the uncertainties and error correlations between Sentinel-3A and Sentinel-3B RRS products. The study finds that, while the validation results are consistent between the two satellites, the RRS data from Sentinel-3B tend to be lower than those from Sentinel-3A, particularly during the post-tandem phase. The compatibility analysis suggests that, while some sites show better agreement, the overall compatibility between daily RRS data from Sentinel-3A and Sentinel-3B cannot be fully established based on the current data.

 

Overall, the paper is well-written and appears to have no major logical or grammatical errors. The methods are clearly described, the results are presented in a structured manner, and the discussion and conclusions are coherent.

 

1.     Please conduct a full text check again, there may be some minor errors. Such as Line 29: [4]1.

 

2.     Line 515, the sentence "These differences in behavior between the EUM and l2gen RRS products could be explained by differences in calibration (possibly generating systematic effects) and differences existing between the associated algorithms (even though they share some common elements)." could be rephrased for clarity, such as "The differences in behavior between the EUM and l2gen RRS products may be attributed to variations in calibration, which could introduce systematic effects, as well as differences in the underlying algorithms, despite their shared components."

 

3.     Line 531, the sentence "Certainly, intertwined effects of geometry and cameras can not be excluded." contains a grammatical error. It should be corrected to "Certainly, the intertwined effects of geometry and cameras cannot be excluded."

Comments for author File: Comments.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1.      The abstract definitely needs to be reorganized, as readers will not appreciate such an unclear summary. The author should emphasize the significance and necessity of the research findings.

2.      The introduction section is difficult to read; the author may need to restructure the narrative to help the reader understand the focus and necessity of this study.

3.      Section 2.1 is poorly written; the author needs to clearly specify the satellite data used.

4.      It is evident that Section 2.2 requires a visual representation to indicate the locations of the field observation sites. Currently, there is no information about their water depth, distance from the shore, or specific ocean current influences.

This does not mean the subsequent content is without issues, but the author needs to rewrite the earlier chapters, as they are extremely difficult to read.

Comments on the Quality of English Language

When writing, the author needs to establish a central narrative thread, ensure coherence in the context, and create connections between paragraphs.