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### Kd490 calculation/formula

Posted: Fri Jun 19, 2020 1:51 pm America/New_York
Dear ocean color team,

I am extracting four MODIS (Level 03) parameters SST, Chl-a, DOC, FLH and eleven reflectance bands time-series from google earth engine. I couldn't find the rest of ocean color variables. I am trying to calculate Kd490 and other parameters like Zeu_morel (euphotic depth), Zsd_morel (Secchi disk depth), tindx_morel (turbidity index) bbp_547_giop (particulate backscattering coefficient) from the reflectance bands. Which one of these variables are easy to calculate using band ratio? and what is the formula to do so? I found some formulas on this website but they seem like more theoretical formulas than practical!

I read this in one of the posts.  "The input ratio for Kd490 is Rrs488 / Rrs547"
Is this formula correct for Kd490?

Thank you so much
Sincerely,
Mo.

### Kd490 calculation/formula

Posted: Fri Jun 26, 2020 9:24 am America/New_York
Mo,

Most of those products are easily computed (e.g. uses a simple equation)...Kd_490 (based on an Rrs ratio),  the Zeu/sd_morel products (based on chl), and tindx_morel (based on chl and Rrs).  GIOP, well that's more complex.

The Kd_490 is described here: https://oceancolor.gsfc.nasa.gov/atbd/kd_490/
The Zsd/eu_morel algorithms are described here: https://doi.org/10.1016/j.rse.2007.03.012
tindx_morel is described here: https://doi.org/10.1016/j.rse.2006.01.022
GIOP is described here:https://doi.org/10.1364/ao.52.002019

Regards,
Sean

### Kd490 calculation/formula

Posted: Fri Jun 26, 2020 10:59 am America/New_York
There are references for some products in `\$OCSSWROOT/share/common/product.xml`, but I only found the GIOP reference (and the DOI was missing).

### Kd490 calculation/formula

Posted: Fri Jun 26, 2020 11:35 am America/New_York
Yes, we probably should flush out the references in there (it's used for the product metadata)...the DOI for the GIOP paper was added by OSA after we added the reference to the product.xml file :grin:

Sean

### Kd490 calculation/formula

Posted: Thu Jul 02, 2020 11:56 am America/New_York
Thank you so very much, Sean:smile:

Sincerely,
Mo

### Re: Kd490 calculation/formula

Posted: Tue Nov 29, 2022 8:45 pm America/New_York
How should it be written in band math expression? I saw the algorithm: log10(Kbio(490))=a0+∑i=14ai(log10(RrsλblueRrsλgreen))i

Kd_490=Kbio(490)+0.0166

but how should it be implemented in SeaDas?

Can you reply with a screen shot of the written expression in the program?

### Re: Kd490 calculation/formula

Posted: Tue Dec 06, 2022 10:30 am America/New_York
Regarding the last question ...

Using the equation and coefficients currently posted at:
https://oceancolor.gsfc.nasa.gov/atbd/kd/

here's a screenshot of what the MathBand tool would look like to create Kd_490 from the Rrs bands
Screen Shot 2022-12-06 at 10.14.28 AM.png (390.18 KiB) Not viewed yet