Chlorophyll concentration OCI VS Chlorophyll Concentration OCX Algorithm

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captain_universe
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Joined: Fri Jan 15, 2021 5:13 pm America/New_York

Chlorophyll concentration OCI VS Chlorophyll Concentration OCX Algorithm

Hello
I am currently doing a research in Marine protected areas (MPA), calculating Chlorophyll concentration through remote sensing.

I started using Terra Modis data but I dont know which of the 2 types I should use. OCX Algorithm OR OCI?

Also I read some papers referring that (OCI) algorithm is a hybrid between a bandâ€difference color index algorithm for lowâ€Chl waters
and the traditional bandâ€ratio algorithms (OCx) for higherâ€Chl waters. Does that mean that OCI contains OCX alogorithm with some more information? I am a little bit confused there.

When I used the OCX Algorithm the size of the file is 5 to 6 times bigger than OCI. Does that mean OCX Algorithm contains more information about variation?

Which of the 2 types should I use in my research and what type is the newest containing more information?

Thank you.

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OB.DAAC - SeanBailey
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Chlorophyll concentration OCI VS Chlorophyll Concentration OCX Algorithm

Use OCI.  As implemented in l2gen  OCI is a blend of the Hu et al., (2012) color index algorithm (which uses a band difference  approach) and the OCx (in the case of MODIS the x is 3, for 3-band ratio algorithm).  See https://oceancolor.gsfc.nasa.gov/atbd/chlor_a/.

I do not understand your statement that the OCX file size is 5 to6 times bigger than OCI, as OCI includes OCX, but switches to the band difference algorithm below concentrations 0f 0.15 mg m^-3, using a weighted average between 0.15 and 0.2 mg m^-3 and is OCX-only above 0.2 mg m^-3 .

Regards,
Sean

captain_universe
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Joined: Fri Jan 15, 2021 5:13 pm America/New_York

Chlorophyll concentration OCI VS Chlorophyll Concentration OCX Algorithm

Thank you for your immediate response.

When I said about the file I meant that the size of OCX (netCDF) is 300 MB (megabytes) while OCI is 40-50MB (megabytes) and I thought the bigger the file the more information will be included.

I will use OCI.

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Chlorophyll concentration OCI VS Chlorophyll Concentration OCX Algorithm

The size of the OCI and OCX are both float, so they will be the same size in an L2 file.  The only way the L2 files could be a different size is if more products were put on one of the files.  You can use "ncdump -h" on the command line or look at the list of bands using SeaDAS.

don