C2RCC Conversion Coefficient for Chl-a and TSM

[torres6]

Good Day.

How can I compute for the appropriate TSM factor bpart/bwit and Chl exponent/factor in the C2RCC parameters? Do I need to obtain first in-situ TSM and Chl values in order to compute for them?

[marpet]

Hi,

similar question was already discussed here:

Retriving chlorophyll and turbidity from sentinel data

The quality can be different for different regions. You should have insitu data to compare the results with real data. As @ABraun said, you.can provide salinity and temperature to improve the results. Also the factors and exponen for tsm and chl computation can be adapted to match your region. [image] You have to find out which values are best. When opening the properties for the band you can edit the values. [image] Once you found good values you can provide them to the processing.

The provided values give good general results with the neural net. But for special region they might need to be adapted. For doing this adaptation you need in-situ data.

[Ceren]

Thanks for explanation. I also need to know what is the chlorophyll exponent and chlorophyll factor. As I understand factor is in-situ value ? could you please answer me.

[marpet]

I think this post can answer your question:

C2RCC_more_information

Hi Ximena! These factors are the conversion from IOPs to concentrations on the bases of empirical relationships. For OLCI you have: chl = 21.0 ∗ (a_pig443)^1.04 tsm= 1.06 * (bp + bw)^0.942 The factors and exponents were derived with NOMAD data mainly (and some coastal data). If you have your own data measured in situ, you could try to derive this relationship by yourself and change the factors conveniently to your study area. That should improved the conversion to fit ranges closer to your …

[Ceren]

your explanation is very clear, thank you.

[solana_0818]

Hi,
I have questions about the factor and exponents, hope you can help with.
If we have in-situ data and want to change the factors and exponents (21.0 and 1.04), and was wondering how can we change it? are there any standard requirements that need to be followed?
Or we just randomly change it like from 21 to 20, without any explainations to see if the conversion fit ranges closer to our observation data (of course the air pressure and ozone remains the same)?
thanks

[marpet]

Yes, it is more like changing the values by good guesses than following some exact procedure.

Following some general advice:
The native output of the neural nets are inherent optical properties (absorption and scattering) of the water. Their magnitude relates to mass concentrations of water constituents, like Chl-a pigment or total suspended matter. The conversion of IOPs into mass concentration depends on the specific properties of the water and may depend on local conditions. How the default values have been derived is mentioned on the C2RCC Community site on the Neural Net page in the section IOP to concentration conversion.

To find the best conversion factor for your area, you need to have in-situ data and compare them with the processing results of C2RCC. You can use the mentioned equation to plot the C2RCC data and vary the factor and exponent values till you found a good match between in-situ data and the result of the equation. Afterwards you can reprocess the data with the new conversion values.

A helpful source on how to do this can be found here: How to Fit an Equation to Data in Excel - EngineerExcel