The value is nan for chlor_a from MODIS

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megasaputra8
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Joined: Sun Dec 27, 2020 10:57 pm America/New_York

The value is nan for chlor_a from MODIS

by megasaputra8 » Wed Jan 27, 2021 11:46 pm America/New_York

Dear all,
I have run l2gen for MODIS data. I want to extract chlor_a. But the result value is nan. Why ?
While for other date MODIS data, the data is not nan.

The MODIS data is in : https://1drv.ms/u/s!AjXAWS5maHffhyu6DmUAGwxoJaJq?e=eUzkBf
I put the result of chlor in that link.

Thank you.

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OB SeaDAS - dshea
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Subject Matter Expert
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The value is nan for chlor_a from MODIS

by OB SeaDAS - dshea » Thu Jan 28, 2021 11:27 am America/New_York

Looks like this is a night time file.  All pixels PRODFAIL and HISOLZEN.  L2gen flagged it as :day_night_flag = "Night"

can't get chl at night.

don

gnwiii
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Joined: Fri Jan 29, 2021 5:51 pm America/New_York
Answers: 1

The value is nan for chlor_a from MODIS

by gnwiii » Thu Jan 28, 2021 11:49 am America/New_York

l2gen output includes a summary of flags:

[...]
Flag #13:         HISOLZEN    5524320  86.4407
[...]
Flag #31:         PRODFAIL    6390880 100.0000


The HISOLZEN flag indicates the sun is close to the horizon, so
you should not expect useful results.

You can also see the percentages in the NetCDF metadata:
$ ncdump -h chla
[...]
group: flag_percentages {

    // group attributes:
                :ATMFAIL = 0.f ;
                :LAND = 26.62129f ;
                :PRODWARN = 0.f ;
                :HIGLINT = 0.f ;
                :HILT = 0.f ;
                :HISATZEN = 5.927666f ;
                :COASTZ = 4.799761f ;
                :SPARE = 0.f ;
                :STRAYLIGHT = 0.f ;
                :CLDICE = 0.f ;
                :COCCOLITH = 0.f ;
                :TURBIDW = 0.f ;
                :HISOLZEN = 86.44067f ;
                :LOWLW = 0.f ;
                :CHLFAIL = 0.f ;
                :NAVWARN = 13.34746f ;
                :ABSAER = 0.f ;
                :MAXAERITER = 0.f ;
                :MODGLINT = 0.6738195f ;
                :CHLWARN = 0.f ;
                :ATMWARN = 0.f ;
                :SEAICE = 0.f ;
                :NAVFAIL = 13.55932f ;
                :FILTER = 0.f ;
                :BOWTIEDEL = 0.f ;
                :HIPOL = 0.f ;
                :PRODFAIL = 100.f ;
    } // group flag_percentages

megasaputra8
Posts: 15
Joined: Sun Dec 27, 2020 10:57 pm America/New_York

The value is nan for chlor_a from MODIS

by megasaputra8 » Sun Jan 31, 2021 6:33 pm America/New_York

oh I see.
I did't see the time of acquisition.
Thank you for your information

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