Retrieval of Chla Concentrations in Lake Xingkai Using OLCI Images

Round 1

Reviewer 1 Report

Lake Xingkai is an important international lake for China and Russia. Remote sensing technology can play an essential supplement to the traditional sampling method to help monitor and protect lakes' health. This manuscript used the OLCI data to monitor the Chla concentrations of Lake Xingkai. But my concerns are mainly on the significance and the novelty of this work. A few comments are listed below:

1. The introduction can be improved. Why the Chla need to be monitored in lakes? What Chla represents? How lake eutrophication monitored by satellite data? You may refer to the articles below:

Wang et al. Trophic state assessment of global inland waters using a MODIS-derived Forel-Ule index[J]. Remote Sensing of Environment, 2018, 217, 444-460.

2. This manuscript provides a simple NIR bright white aerosol atmospheric correction method. However, why not use the OLCI's water-leaving reflectance data directly? We found no comparison results of in situ Rrs and OLCI retrieved Rrs in the content. The comparison was essential to support retrieving long-time series OLCI Chla products.

3. Section 2.4. More information should be added about the mechanical background of the Chla algorithms.

4. Many units are not superscripted or subscripted, such as mg m-3. The authors should check all the units carefully in the manuscript.

5. Figure 4. I think there is no information delivered by the marks with different colors and shapes. We can see the contribution of each constituents with the triangle coordinates. But you may add some information on how the FBA algorithm perform with different  constituent contribution. This can be a good contribution of this paper.

6. Why the FBA outperformed other algorithms in Lake Xingkai?

7. The definition of high solz and senz differed from the definition of the ocean. The threshold was much smaller than That is a point that needs more discussion.

8. In Page 12, “The R2 of FBA, TBA BR, and FLH decreased from 0.67, 0.58, and 0.60, to 0.56 to 0.40, 0.23, 0.19, and 0.46, respectively.” There was an extra “to”.

The language should be improved.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The work is devoted to assessing the accuracy of determining Chla concentrations in Lake Shinkai using OLCI images. The values of chlorophyll "a" concentration collected during the 2018 expeditions and calculated according to the latest OLCI-SENTINEL-3 satellite radiometers were compared. Comparison of traditional in-situ data and modern remote sensing data made it possible to calculate errors in calculating the concentration of chlorophyll "a" by standard processing algorithms. Verification of satellite values processed by standard algorithms for calculating the concentration of chlorophyll "a" showed a weak connection with field measurements and corresponding large errors for the studied area of Lake Xingkai. 

According to the authors, the four-band model (FBA) is the most effective model, however, of course, the value of the average absolute percentage difference of 38.26% is not a good indicator.  From my point of view, the article can be published, provided that the conclusion is reformulated (because it poorly reflects the main conclusions of the work and does not contain information about the prospects for improving the results obtained). 

Line 192-194 (formula) needs formatting

The first half of the article is not in doubt, and therefore I would like all further calculations to be accompanied by formulas and figures and graphs that explain the results and the discussion section in more detail.

In the list of references, after 62 sources, source 1 appears again (perhaps it is superfluous or 1 source has not been replaced).

Best regards

Author Response

please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I recommend to accept if for publication now