Earthdata Forum

Posted: **Sat Oct 10, 2020 11:14 pm America/New_York**

I compared aph value of the QAA between l2gen and Excel file found in IOOCG web site using a same Rrs input.
Output from the excel file is different from l2gen output. So, I have looked through the QAA source code of l2gen.
https://oceancolor.gsfc.nasa.gov/docs/ocssw/qaa_8c_source.html
According to the pdf file "Update of the Quasi-Analytical Algorithm (QAA_v6)", the equations in the code,

numer = Rrs[idx440] + Rrs[idx490];
denom = Rrs[idx555] + 5 * Rrs[idx670]*(Rrs[idx670] / Rrs[idx490]);

in lines 241-242 and 327-328 might be

numer = rrs[idx440] + rrs[idx490];
denom = rrs[idx555] + 5 * rrs[idx670]*(rrs[idx670] / rrs[idx490]);

Thanks.

Toru

Posted: **Mon Oct 12, 2020 12:34 am America/New_York**

Hi Toru,

I agree that as per the QAA v5/v6 documentation, the reflectance terms in lines 241-242 and 327-328 probably should be sub-surface and not above-water reflectances. I shall look into this further.

Best regards,
Lachlan

Posted: **Tue Oct 13, 2020 6:49 pm America/New_York**

Hi - You might also have a look at https://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=38558

Posted: **Thu Oct 15, 2020 12:18 am America/New_York**

Hello Lachlan,

Thanks!
I hope this will be updated in the next version.

Toru

Posted: **Thu Oct 15, 2020 12:25 am America/New_York**

Thanks Barry, for the notice. Equation for the Rrs(670)>0.0015 sr-1 seems to be corrected. Toru