Cloud Masking

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avmehta
Posts: 150
Joined: Mon Feb 03, 2020 10:27 am America/New_York

Cloud Masking

by avmehta » Tue Sep 15, 2020 6:42 pm America/New_York

Hello,
    In the SeaDAS GUI there is a way to get 50 m land mask from SRTM. Is there a way to use this mask when running l2gen on linux?
    Also, I see the following answer in the forum from Norman. Could you please help with how to set rhos_865 threshold to mask land and clouds in OLI images?
    Would similar method work for MSI also?
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"Topic Geolocation issue with l2gen By norman Date 2020-03-27 12:49

For Landsat, I would suggest that you not use the land-mask that comes along with
l2gen; it is just not of high enough resolution or accuracy.  When I need to discriminate
between land and water in Landsat 8 data, I like to compute rhos_865 from Band 5
and choose a threshold reflectance to generate a radiometric land/cloud mask.
To avoid the supplied land-mask, I pass these two options to l2gen.
land=$OCDATAROOT/common/landmask_null.dat   maskland=0"
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Thank you
Amita

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OB WebDev - norman
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Cloud Masking

by OB WebDev - norman » Wed Sep 16, 2020 9:22 am America/New_York

Hi Amita,

I will leave it to the SeaDAS experts to answer the SeaDAS related questions.

After using l2gen to generate rhos_8xx products, I usually map the data to a 16-bit image
and then use Gimp Colors->Levels... to interactively choose a threshold that separates
land and clouds from water.  The threshold I end up with depends a bit on how much
suspended sediment and/or surface slicks are in (or on) the water.

I suspect that SeaDAS may have something similar that you could use for interactively
choosing a threshold.  Again, I defer to the SeaDAS experts.

Norman

OB SeaDAS - knowles
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Cloud Masking

by OB SeaDAS - knowles » Thu Sep 17, 2020 9:53 am America/New_York

Hi Amita,

I'm answering in regards to how you would do cloud masking on a rhos_865 band with other SeaDAS GUI tools instead of cloud masking with l2gen.

In the Mask Manager tool window click on "f(x)" icon.  Click "Show bands".  At this point you can click and create a math expression based on the rhos_865 band.  Alternatively you can type it directly into the window.

Here is a sample expression you could use based on our default cloud threshold:
"rhos_865 > 0.027"

After clicking OK the cloud mask is created and displayed in the SeaDAS GUI.

Danny

avmehta
Posts: 150
Joined: Mon Feb 03, 2020 10:27 am America/New_York

Cloud Masking

by avmehta » Mon Sep 21, 2020 12:03 pm America/New_York

Thanks Danny.
Amita

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