Selecting reflectance math band

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octavioeg
Posts: 2
Joined: Mon Nov 04, 2019 10:02 am America/New_York

Selecting reflectance math band

by octavioeg » Mon May 23, 2022 2:32 pm America/New_York

Hello,
I want to improve the Chl a concentration data in the Southern Ocean, specifically Drake Passage.
I found this algorithm Chl=exp10(0.3205-2.9139R+8.7428R2-16.1811R3+9.0051R4)
R=log10(Rrs(443/555)>Rrs(490/555)>Rrs(510/555))
for Globcolour data. In this paper https://doi.org/10.1002/jgrc.20270

I trying to use math band to select greatest reflectance proportion, however my programing knowledge is very limited
Tried something like: if log10(443/555)>log10(490/555)>log10(510/555) then log10(443/555) else log10(490/555)>log10(510/555).

Or maybe I can do it separately and see which one is greatest.
Some one can give me a hint?
Thanks,

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OB SeaDAS - knowles
Subject Matter Expert
Subject Matter Expert
Posts: 250
Joined: Mon Apr 07, 2008 4:40 pm America/New_York

Re: Selecting reflectance math band

by OB SeaDAS - knowles » Tue May 24, 2022 4:49 pm America/New_York

The BandMath expression to replicate the Chl GlobColour equation 6 of the paper you reference would be:

First create band named R:

Code: Select all

if (log10(Rrs_443/Rrs_555) > log10(Rrs_490/Rrs_555) 
    and log10(Rrs_443/Rrs_555) > log10(Rrs_510/Rrs_555))
then 
    log10(Rrs_443/Rrs_555)
else 
(
    if (log10(Rrs_490/Rrs_555) > log10(Rrs_510/Rrs_555))
    then 
        log10(Rrs_490/Rrs_555)
    else
        log10(Rrs_510/Rrs_555)
)
Then apply the coefficients to create the Chl band:

Code: Select all

exp10(0.3205
-2.9139 * R 
+ 8.7428 * pow(R,2)  
-16.1811 * pow(R,3) 
+ 9.0051 *pow(R,4)) 

octavioeg
Posts: 2
Joined: Mon Nov 04, 2019 10:02 am America/New_York

Re: Selecting reflectance math band

by octavioeg » Tue May 24, 2022 9:01 pm America/New_York

Thanks a lot!

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