Introducing Two Fixed Platforms in the Yellow Sea and East China Sea Supporting Long-Term Satellite Ocean Color Validation: Preliminary Data and Results
, Shuguo Chen 1,3,4,5,*, Lianbo Hu 3,5, Xi Wang 1,2, Xinhao Shi 3, Xueyin Li 3, Linke Deng 4 and Chaofei Ma 1,2
Giuseppe Zibordi
Round 1
Reviewer 1 Report
The manuscript by Qingjun Song et al. presents the status of two AERONET-OC like validation sites established in the Yellow Sea and East China Sea. The manuscript is well written (even though requiring some minor editorial revisions for the English). The content well fits with requirements for publishing in "Remote Sensing" and it is of general interest for the ocean color scientific community. I would recommend publishing the manuscript "as is", with the exception of some check for the English language (for the benefit of the authors, I am providing copy of the manuscript with suggested edits).
Comments for author File: 
Comments.pdf
Author Response
Dear Dr. Giuseppe Zibordi,
We thank you for your insightful comments. We have carefully reviewed these comments and revised the manuscript accordingly.
Sincerely,
Qingjun Song , Shuguo Chen , Lianbo Hu , Xi Wang, Xinhao Shi, Xueyin Li, Linke Deng and Chaofei Ma
Author Response File: Author Response.pdf
Reviewer 2 Report
TITLE: Two long-term fixed platforms in the Yellow Sea and East China Sea supporting satellite ocean color validation: design, deployment, and preliminary data results
AUTHORS: Qingjun Song, Shuguo Chen , Lianbo Hu , Xi Wang, Xinhao Shi, Xueyin Li, Linke Deng and Chaofei Ma.
SUMMARY and COMMENTS
The authors validate two AERONET-OC sensors deployed in Muping and Dong’ou, China. The evaluation included Rrs and AOD products using in-situ measurements. Intercomparison between the two AERONET-OC sensors and satellite products from three sensors (MODIS, OLCI and MSI) was also conducted.
The authors did not provide a clear objectives for the current studies which influence the ability of the reviewer to evaluate the importance of some figures & topics. On the other hand, the discussion section did not provided an interpretation for the significant results, however, it introduce a new simulated data which did not described in the methods section. Finally, the authors considered L1 data from MSI sensor associated with comparison of several atmospheric correction models. The outputs did not provide any significant finding related to the comparison. This raises questions related to the need to consider MSI sensors that are not as ocean color sensors. The detailed comments are as follows:
Major comments:
1. The authors did not clearly mention the objectives of the current study in the last paragraph of the introduction section.
2. The discussion section should provide interpretation for significant results rather than introduce new results and figures. For instance, the discussion should discuss
why do blue bands provide higher error compared with longer wavelengths?
Why was MRPD of Rrs relatively high compared with AOD? etc
3. In addition, in Lines 431~434, The authors did not provide any information related to simulated Rrs they used to compare SeaPRISM vs. MODIS and SeaPRISM vs. MSI. The authors should answer the following questions
which technique do they use to conduct the simulation?
What IOPs parameters did they consider?
Did they measure any absorption & backscattering?
Why are only 270 stations shown in Figure 15?
Did the simulation results have any influence on the study objectives?
4. The authors discuss the atmospheric correction of the MSI sensor, which, I believe, does not fit the current study's objective. The authors should explain the reason for selecting the MSI sensor and the need to discuss various atmospheric correction models.
5. The outline of statistical analysis should be discussed in section 3.
Other comments
ü Line 19: remove dot (.) after "reflectance (Rrs)."
ü Line 24: the statement "with each other," is vague. It is better to clearly mentioned which measurement vs which measurements. Please update similar statement in the conclusion section.
ü Line 25: The statement "high quality" is not accurate, and it is better to be replaced or removed.
ü Line 37: for the statement "on the sea surface", Replace "on" with "just above"
ü Lines 58~59: One of the six sites is located in Arabian Gulf. Thus, please update the statement and move the details of six sites to section 2.
ü Line 75: The name Dong'ou site has a typo in Figure 1 & Figure 13 as the quote is missing.
ü Line 86: add the word "respectively" after "East China Sea."
ü Line 111: it is recommended to mention the height of The platform at the Dong'ou site
ü Lines 121~123: the statement related to SeaPRISM sensor is not clear.
For instance, "steel structure with a height of 3 m" is this the height measured from the roof?
It is better to mentioned the sensor height from water level.
ü Line 127: replace "was deployed" with "were deployed".
ü Figure 2: White arrows are hard to see.
ü Lines 163~164: the statement "?? and ?? are the SeaPRISM measured sky and total water radiance" should be "?? and ?? are the SeaPRISM measured total water radiance and sky" by swapping the sky and total water radiance.
ü Line 182: It is recommended that the authors provide a brief description of Lee's BRDF correction scheme [34].
ü Equation 5: It is recommended to replace the integral symbol with a summation. Authors do not need the shorten the acronym SRF to S. It is also recommended to use SRF in the equation. It is also recommended to use Relative SRF instead of SRF.
ü Equation 5 & Figure 14: Figure 14 should be moved into section 3 near the discussion of the SRF in eq. 5. Please also provide a reference to the SRF of SeaPRISM
ü Line 219: there is no need to "In contrast,"
ü Figure 4: it is recommended to align the start date of both Fig 4a & 4b by shifting the start date of Fig. 4b " i.e., Jan-2020" to be aligned with Fig. 4a. Similar comment for Figure 6.
ü Lines 236~239: the sites' order in Line 237 is Dong'ou and Muping. However, the former and latter refer to Muping & Dong'ou (opposite order).
ü Lines 260~272: these lines are very confusing and should be rephrased and these detailed should be discussed in section2. The statement in line 272~273 "comparisons between SeaPRISM and CE318-TS and between SeaPRISM and SeaPRISM were made separately. " summarizes all these confusing lines.
ü Line 273: is this statement " SeaPRISM and SeaPRISM " means that there are two SeaPRISM? But figure 2 shows only one SeaPRISM. Authors could also use number notation for the two SeaPRISM (e.g., SeaPRISM1 & SeaPRISM2).
ü Line 274: what is binned mean?
ü Line 319: The authors mentioned, " The Rrs values were extracted at the four visible bands for MODIS and OLCI. " whereas figures 9a & 9b illustrate more than four bands.
ü Figure 13: The figure resolution is low, and I could not see the Muping site among the legend unless it was represented using a different name.
ü Line 424: replace " band with " with "bandwidth".
ü Figure 15: There is no statistics evaluation shown in the figure (e.g., RMSE, MRPD)
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 3 Report
attached as pdf
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
General appraisal.
The manuscript by Qingjun Song and co-authors provides a quite comprehensive description of two newly developed platforms dedicated to supporting validation of satellite ocean colour products in shallow water environments.
The subject is appropriate for publication in Remote Sensing.
The manuscript writing, language accuracy, organisation and length are satisfactory.
I recommend publication after the following comments have been taken into account.
Specific and detailed comments.
- Abstract, line 19: the remote sensing reflectance is not “observed”. It is calculated from the observed quantities, which are the sea and sky radiances.
- Introduction, line 32: you should use the “ocean colour radiometry” terminology, not just “ocean colour”
- Line 37: imprecise writing. Rrs is the ratio of the water-leaving radiance to the downward irradiance just above the surface.
- Line 42: “.. that varied with the vicarious calibration site”. Unclear. Rephrase or remove.
- I suggest Fig.1 to be completed by a zoomed map of the area where the two platforms are deployed, on a background of, e.g., the annual average of chlorophyll or total suspended matter.
- Line 94: “optically deep” is used to depict clear waters where light can propagate quite deep, not the opposite. Here you actually refer to quite shallow (depth is 18 m) and turbid waters.
- Line 94-95: again, if the water is optically deep, you have actually more chance (or risk) to see the bottom.
- Lines 109-112: not sure why you use the past tense here and for many subsequent paragraphs, when you describe existing equipment. Present tense should be used.
- Lines 114 and subsequent. More details of manufacturers (not just the name) must be added when introducing instruments. Like “Cimel Electronique, Paris, France” or “TriOS Mess- und Datentechnik GmbH, Rastede, Germany”.
- Line 151: the SeaPRISM and CE318-TS photometers do not measure irradiance. They only measure radiances, from which you will then derive the aerosol optical thickness, then to be used in your Eq. (3) to compute irradiance.
- Ed is Eqs. (2) and (3) and the rest of the paper could be referred to either as Ed(0+) or Es, in order to more clearly express that they are the value just above the sea surface.
- Eq. (5) is incorrect. The hyperspectral Lw should be convolved by the sensor spectral band response function (SRF), then the hyperspectral Ed should be convolved by the same SRF, and the ratio of the two quantities will then give the Rrs for the spectral band in question. I suspect this is actually what has been done and Eq. (5) was incorrectly written. This is important for section 5.2 to be meaningful.
- Lines 206-208: that should rather appear in the figure legend. No need to congest the text with this.
- Line 238 and subsequent: units should be given when Rrs values are reported.
- Section 4.2: I do not understand what the SeaPRIMS vs. SeaPRISM comparison is. This should be made clearer. I may have missed something but I do not think it is said that two SeaPRISM are deployed.
- (a) and (b) are missing on panels of Fig. 5.
- Overall, the fonts used in Figures are way too small.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors carefully addressed my comments and provided point-to-point responses.
I have three minor comments as follows:
Line 218: the reference of Mobley 1999, mentioned rho = 0.028. I believe that the authors should cite Mobley 2015 as follows:
Mobley, C.D., 2015. Polarized reflectance and transmittance properties of wind-blown sea surfaces. Appl. Optics 54(15), 4828-4849.
Figure 3: It is recommended to use primary & secondary axes for absorption and backscattering or use tow side-by-side figures for each parameter.
Figure 6: the word "Density" should be deleted
Author Response
Dear Reviewer,
We thank you for your insightful comments. We have carefully reviewed these comments and revised the manuscript accordingly. In the following, we provide point-to-point responses to those comments.
Sincerely,
Shuguo Chen
The authors carefully addressed my comments and provided point-to-point responses.
I have three minor comments as follows:
Thank you.
Q: Line 218: the reference of Mobley 1999, mentioned rho = 0.028. I believe that the authors should cite Mobley 2015 as follows:
Mobley, C.D., 2015. Polarized reflectance and transmittance properties of wind-blown sea surfaces. Appl. Optics 54(15), 4828-4849.
A: Mobley (1999,AO) studied the sea surface reflectance (rho) behavior using numerical simulations for unpolarized light and found the values of rho varied with sun zenith angle, viewing geometry, wind speed and sky radiance distribution. The minimum value of rho occurs at viewing zenith angle of 40 deg and relative azimuth angle of 135 deg when wind speed is < 15 m/s. Mobley (1999,AO) generated a look-up table of rho for different sun zenith angle, viewing geometry and wind speed. In the manuscript, we used the rho values derived from the look-up table based on the setup geometry of radiometers and concurrent measured wind speed.
Similar studies were done by Mobley (2015,AO) but for polarized light and similar look-up table was generated. More factors will contribute to the value of rho for polarized light making it more difficult to determine in the real environment condition. For example, the value of rho depends on the wind speed and sky radiance distribution for unpolarized light but it will also depend on the wind direction and polarization state of sky radiance for polarized light. Therefore, for the same viewing geometry, the values of rho for polarized light have a factor-of-two spread than those for unpolarized light. Because some polarization measurements were unavailable, we calculated rho from the look-up table generated by Mobley (1999,AO) for unpolarized light in this manuscript.
This is a good suggestion. We will implement the work by Mobley (2015, AO) in the further study.
Q: Figure 3: It is recommended to use primary & secondary axes for absorption and backscattering or use tow side-by-side figures for each parameter.
A: It’s a good suggestion. We updated Figure 3 and the corresponding caption in the revision using the left y-axis for absorption and right y-axis for backscattering.
Q: Figure 6: the word "Density" should be deleted
A: ‘Density’ was deleted in the revision.
