Data Quality of MODIS aqua level-3 chlorophyll-a and need of Regional Algorithm

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antu
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Data Quality of MODIS aqua level-3 chlorophyll-a and need of Regional Algorithm

by antu » Mon Mar 02, 2020 11:13 pm America/New_York

We have been investigating the annual/seasonal variability of chlorophyll-a concentration and its relationship with sea-surface temperature and river discharge in coastal shelf region of northern Bay of Bengal (Norther Indian Ocean) and validate MODIA Aqua chl-a data with in-situ measurement. We used 16 years’ level- 3 MODIS aqua chl-a (OCI algorithm) data for our study. But, we are facing several questions related to data from scientific community while publishing paper. The question was quoted below …

“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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GES DISC - jimacker
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Re: Data Quality of MODIS aqua level-3 chlorophyll-a and need of Regional Algorithm

by GES DISC - jimacker » Tue Mar 03, 2020 3:23 pm America/New_York

Dear Antu,

Thank you for an excellent question. However, the appropriate Distributed Active Archive Center (DAAC) to answer your question is the Ocean Biology DAAC, OB.DAAC, https://oceancolor.gsfc.nasa.gov. The OB.DAAC has a User Forum that is dedicated to answering questions from the ocean color data user community, and can apply considerable scientific expertise to your question. Furthermore, the OB.DAAC forum has been in operation for several years, and a Subject search may immediately provide information relevant to your question.

The link to the OB.DAAC forum is https://oceancolor.gsfc.nasa.gov/forum/ ... um_show.pl

Regards,
Jim Acker

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