Question about OceanColor solar irradiance (F0) and nLw units

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imaginaryfish
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Question about OceanColor solar irradiance (F0) and nLw units

by imaginaryfish » Wed Sep 28, 2022 11:52 am America/New_York

Hello,
I am new to processing ocean color data and I am working on converting RRS to nLw. However, I think either I am not understanding something or there is an error on the OceanColor website where F0 is listed (https://oceancolor.gsfc.nasa.gov/docs/rsr/rsr_tables/).

For each sensor/platform the units listed for F0 is W/m^2/um/sr. However, I thought that the units for nLw is W/m^2/um/sr. If F0 units are W/m^2/um/sr, then that would make nLw units W/m^2/um, but that is not correct according to my understanding.

So, the question is what are the units for F0 and nLW?

Thank you in advance,
Brendan

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Re: Question about OceanColor solar irradiance (F0) and nLw units

by OB.DAAC - SeanBailey » Thu Sep 29, 2022 6:55 am America/New_York

Brendan,
Nice catch...The units of F0 on that page are incorrect and should be W/m^2/um (nLw are W/m^2/um/sr).
We'll update the web documentation.

Thanks,
Sean

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Re: Question about OceanColor solar irradiance (F0) and nLw units

by imaginaryfish » Thu Sep 29, 2022 9:48 am America/New_York

Thank you Sean! Good to know I am learning and my knowledge is somewhat accurate.

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Re: Question about OceanColor solar irradiance (F0) and nLw units

by OB.DAAC - amscott » Thu Sep 29, 2022 11:01 am America/New_York

Good day! The page has been updated with the correction to the F0 units.

imaginaryfish
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Re: Question about OceanColor solar irradiance (F0) and nLw units

by imaginaryfish » Fri Sep 30, 2022 12:56 pm America/New_York

Forgive the naive question, but which values of F0 should be used to convert between RRS and nLw? There are values given in the metadata in the Aqua MODIS L2 netcdf files and then there is the F0 listed on in these tables (https://oceancolor.gsfc.nasa.gov/docs/rsr/rsr_tables/). And they are not the same.

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Re: Question about OceanColor solar irradiance (F0) and nLw units

by OB.DAAC - SeanBailey » Fri Sep 30, 2022 4:16 pm America/New_York

The Rrs values are typically reported as 10nm wide square band values. The F0 values on the rsr_tables page are fully convolved with the sensor spectral response function. This is not the nominal 10nm square band value. So, the value in the metadata of the L2 file in question is the one to use, as it will be consistent with the Rrs.

Sean

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