“In general, MODIS chlorophyll concentration products provided by NASA were directly used in the paper, without regional correction or regional algorithm inversion, which would lead to the unreliability of the results:
1) The credibility of MODIS chlorophyll concentration products in offshore turbid water bodies is poor and significantly overestimated. The last figure (validation result graph of MODIS data with in-situ measurement) in the paper also proves this problem. Therefore, it is usually necessary to remove these turbid water bodies which are greatly affected by terrestrial sources. However, the analysis in this paper does not seem to exclude the region of turbid water, which will lead to unreliable results.
2) Since the inshore MODIS inversion chlorophyll concentration value is significantly higher than that of the offshore sea, the regional mean value change more reflects the inshore water changes. However, the remote sensing data error of chlorophyll concentration in coastal water is very large. In fact, the chlorophyll concentration inversion in this region is more about the concentration of terrestrial suspended particulates than the real chlorophyll concentration. Therefore, the annual average, seasonal average and long-term variation trends all reflect the distribution and change of suspended matter concentration in water, rather than the distribution and change of chlorophyll concentration.
It is suggested to carry out regional correction of MODIS or regional algorithm inversion”
How can we clarify this query?
As we worked with level-3 data, there are no way to use regional algorithm. Level-3 chl-a data has a build-in algorithm called OCI (OCx and CI combined). Moreover, there need huge work load (time and funding) to form up a regional algorithm, which was not the scope of our study. Developing regional algorithm can be handy to get more accurate results. But without it, can’t we use level-3 data for our study area in scientific study?
I need some really strong and plausible statements regarding this query? We are rigorously questioned about quality of MODIS aqua data.
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the region also suffers from perennially bad air quality. This negatively
affects the accuracy of the MODIS atmospheric correction.
I am afraid your reviewers are correct. Ocean color remote sensing
is difficult even over clear skies and Case 1 waters, so your region
comes with significant additional difficulties.
Yes, the reviewer was right. We understand his point. But how can we provide some statement that support our work? We have no option to do regional correction.
Below is an example for January 2019.
But now we want to know, whether MODIS level-3 chl-a data, itself has any procedures for atmospheric correction, cloud masking, etc for minimizing such type of errors. If it has, is there any documents regarding processing level-3 data or information about the atmospheric correction for MODIS aqua chl-a data.
Thanks in advance.
The Level-3 ocean color products (including chlorophyll) have a number of masking criteria applied to ensure only the best possible data are included.
However, these do not necessarily address the concerns of your reviewers, as there are conditions for which the flagging criteria cannot address or capture.
Specifics on the atmospheric correction can be found in the NASA Technical Memorandum "Atmospheric Correction for Satellite Ocean Color Radiometry"