Preliminary Assessment of On-Orbit Radiometric Calibration Challenges in NOAA-21 VIIRS Reflective Solar Bands (RSBs)
, Slawomir Blonski 1, Xi Shao 3, Wenhui Wang 3 and Khalil Ahmad 1Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors present results from the early-mission on-orbit radiometric calibration of the VIIRS instrument on the latest NOAA polar orbiting satellite. The paper is clearly written and very thorough and is certainly deserving of publication.
The only significant concern I have with this paper is excessive self-citation. This and other minor comments are provided below.
General comments:
1) By any reasonable measure, there is an excessive amount of self-citation. Twenty of the 32 references have a first author that is one of the authors of this paper. While many of these self-references are important, some of them are redundant and could be removed. In addition, there are a few other groups that do independent on-orbit calibration of VIIRS (at least for past VIIRS builds) and their work is not cited at all. This needs to be fixed.
2) In sections 3.6 and 3.7 and in Figs. 12, 13, and 14, the dates presented are very confusing and inconsistent. I am referring to the dates of different versions of H and F derived “using the yaw maneuver data and on-orbit data until [DATE]…” In the text on the H-factor, the dates listed are April 2023 and Nov 2023, but the figures say April 2023 and March 2024. Should they be the same? In the text on the F-factor, the dates are Aug 2023 and Nov 2023, while the Figure says Aug 2023 and March 2023. I assume at least the last one is a typo, but what about the others? Why not just show us two versions (April 2023 and whatever the final one is – March 2024, I assume) and keep it consistent for both H and F plots? With so many versions, it is hard to follow the discussion.
3) Overall, the paper is very clear, and the English usage and grammar are excellent. I noted a few typos and grammar corrections below, but there are several other similarly minor corrections needed that I didn’t bother to write down. Another careful proof-reading is recommended.
Specific comments:
4) Line 23 – “is” possibly due…
5) Line 27 – successful
6) Line 111 – RTA not defined?
7) Line 140 – the nested parentheses following GIRO are a bit confusing, and I think you are missing one, so consider a re-wording of this sentence.
8) Line 150 – ten lunar events?
9) Line 158 – Does this suggest that the lunar image changes depending on the frame? Is that because of some frame-dependence of the calibration, and if so can’t it be taken out?
10) Line 189 – Define LUTs
11) Line 195 – What about the data gaps and changes in data frequency between roughly days 95 and 115 on the Fig 3 plot?
12) Line 211 – NOAA-21?
13) Line 227 – updated set “of”… Also, need to define “delta C”?
14) Line 297 – Some more explanation of the bias corrections would be helpful as they appear to be a very significant (several percent) adjustment to the data. Presumably when you say ‘better agreement with NOAA-20’ you mean that the goal is to have N21 reflectance match N20 VIIRS reflectance, right? If so, why is this limited to the SWIR bands and not the VISNIR bands also? Are the bias factors derived from lunar and DCC data together in some way? Are they applied to the F-factors through the F-PREDICTED-LUT, or the RSBautoCal, or is there some other way they can be added to the products?
15) Line 317 – remove “)”
16) Line 329 – Was the RSBautoCal turned off after the second MMOG? Your plot in Fig. 7 seems to indicate that it is still on, or at least it continues to be plotted after that, so it is not clear.
17) Line 333 – same y-scale as Fig. “8”
18) Line 347 – remove extra ‘of’
19) Line 478 – repetitive; consider re-wording this sentence
20) Line 481 – repeated “could be”
21) Line 483 – Both here and in the DCC sub-section you mention the impact of the solar cycle without giving any details. It is true that the solar cycle has been approaching solar maximum and there has been increased solar activity in the past two years, but why do you think this will affect the DCC reflectance trends? Are you suggesting that the cloud reflectance changes with the solar cycle? The actual radiant output of the Sun in VIS/NIR is very stable even across a solar cycle (as I recall it is within 0.2% even in relatively narrow wavelength ranges), so it seems unlikely that this can matter to your measured DCC trends many of which are more than 0.5% per year. I suppose the changes in solar particle and x-ray flux (which vary by large amounts over a solar cycle) can more directly affect the instrument gain, but this would impact all sources and not be specific to DCC.
Author Response
Please see the attached Word file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper show overviews of initial results for on-orbit NOAA-21 VIIRS radiometric calibration in RSBs. In relation to this, additional research on minor comments should be conducted and supplemented. The minor review opinion is as follows.
1. Is there any progress in the results of the variable calibration?
I understand that on-orbit calibration is of course important, but if the results of the vicarious calibration are also conducted, it will be a more reliable paper.
Minor comments
Line 101: Please enter the full name for the abbreviation (Deep Convective Cloud)
Line 140-141: ')' seems to be missing from GIRO (GSICS Implementation of the ROLO model). Need an addition where appropriate.
Line 164: Please modify to acronyms instead of full name in DCC.
(Related to the correction of line 101)
Line 518: It would be nice to delete/modify the shade in Table A1.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsPlease refer to the attached file.
Comments for author File: Comments.pdf
Clean-ups of the figs (Especially, the titles of the figures) are highly recommended. Titles of the Figs should be relevant and succinct.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have sufficiently addressed all my comments and questions. I don't have any more concerns. The revised manuscript should be published as is.
