How to get the reflectivity from water by modis on seadas

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geoding
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How to get the reflectivity from water by modis on seadas

by geoding » Fri Mar 26, 2021 2:55 am America/New_York

Hello everyone,
When I was using seadas7.5.3--OCSSW--l2gen to process modis data in order to obtain the reflectivity of the water body, I only got the reflectivity of the land and the reflectivity of the water body was negative. What parameters should I set to get the desired result?

Thanks,
ding

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OB SeaDAS - xuanyang02
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Re: How to get the reflectivity from water by modis on seadas

by OB SeaDAS - xuanyang02 » Fri Mar 26, 2021 12:28 pm America/New_York

Can you share with us what L1B file you are using?

geoding
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Re: How to get the reflectivity from water by modis on seadas

by geoding » Tue Apr 06, 2021 8:35 am America/New_York

This is the processed data: A2015017174500.L1B_LAC (Sorry, I cannot add it to the attachment due to the file size limitation), and the value obtained during atmospheric correction Rrs and Lw etc is NaN .

gnwiii
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Answers: 1

Re: How to get the reflectivity from water by modis on seadas

by gnwiii » Tue Apr 06, 2021 9:20 am America/New_York

It might be useful to attach the output from

Code: Select all

ncdump -h  level-2file > file_to_attach.txt
or paste the flag percentages group into a message. It should look like:

Code: Select all

 group: flag_percentages {

    // group attributes:
                :ATMFAIL = 0.002910551f ;
                :LAND = 58.34771f ;
                :PRODWARN = 0.f ;
                :HIGLINT = 8.01977f ;
                :HILT = 74.56316f ;
                :HISATZEN = 6.834702f ;
                :COASTZ = 9.520559f ;
                :SPARE = 0.f ;
                :STRAYLIGHT = 20.76566f ;
                :CLDICE = 49.18076f ;
                :COCCOLITH = 0.05610088f ;
                :TURBIDW = 0.4009649f ;
                :HISOLZEN = 0.f ;
                :LOWLW = 0.4405847f ;
                :CHLFAIL = 0.1281734f ;
                :NAVWARN = 0.f ;
                :ABSAER = 0.f ;
                :MAXAERITER = 0.2457961f ;
                :MODGLINT = 13.04571f ;
                :CHLWARN = 0.06799776f ;
                :ATMWARN = 0.4495347f ;
                :SEAICE = 3.548799f ;
                :NAVFAIL = 0.4926109f ;
                :FILTER = 0.f ;
                :BOWTIEDEL = 0.f ;
                :HIPOL = 0.104416f ;
                :PRODFAIL = 79.90796f ;
    } // group flag_percentages

OB SeaDAS - xuanyang02
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Re: How to get the reflectivity from water by modis on seadas

by OB SeaDAS - xuanyang02 » Tue Apr 06, 2021 1:23 pm America/New_York

The file you chose is at night, there is no sun, therefore no Rrs or Lw.

https://oceancolor.gsfc.nasa.gov/cgi/br ... nc_SST_BRS

geoding
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Re: How to get the reflectivity from water by modis on seadas

by geoding » Tue Apr 06, 2021 9:49 pm America/New_York

ncdump -h level-2file > file_to_attach.txt

Thank you very much,
Unfortunately, I didn't understand how to share data. Does this code :"ncdump -h level-2file > file_to_attach.txt" run in the terminal?
I downloaded daytime and after seadas atmospheric correction l2gen, the result is still NaN.
Attachments
QQ截图20210407101538.jpg
QQ截图20210407101538.jpg (92.68 KiB) Not viewed yet
seadas_day.jpg
seadas_day.jpg (22.34 KiB) Not viewed yet

OB SeaDAS - xuanyang02
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Posts: 127
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Re: How to get the reflectivity from water by modis on seadas

by OB SeaDAS - xuanyang02 » Wed Apr 07, 2021 5:53 pm America/New_York

Screen Shot 2021-04-07 at 5.58.21 PM.png
Screen Shot 2021-04-07 at 5.58.21 PM.png (149.02 KiB) Not viewed yet
You need to place the actual name of level-2file and file_to_attach in the command, like
"ncdump -h A2015017054000.L2_LAC_OC > file_to_attach.txt". Then you can attach the "file_to_attach.txt" here by clicking the "Attachments" tab and clicking "Add files" button.

If you download A2015017054000.L2_LAC_OC.nc, and open it in seadas, you can see there is no data at the point of your interest (23 N, 117 E)

I don't know what products you chose doing l2gen. I made an L2 file A2015017054000RrsLw.L2_LAC_OC with Rrs and Lw as the products. Here is the image for Rrs_469.

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