Polymer cloud cover and land flag

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Fluquorr
Posts: 3
Joined: Tue Apr 26, 2022 5:01 pm
company / institution: City University of New York
Location: New York

Polymer cloud cover and land flag

Post by Fluquorr »

Hi François,

When I process OLI scenes with Polymer and ACOLITE, I found that polymer will fill the cloud-cover areas with values. In contrast, the image processed by ACOLITE has no value for cloud cover area. I wonder how does Polymer get the cloud-cover areas' value? Are these values inferred by Polymer?
Screen Shot 2022-05-31 at 11.22.00 AM.png
The second question is about land flag. When I process OLI scenes with polymer I found some scenes' land flag are not masked out. Do you know how to mask out this land information? Thanks!
Screen Shot 2022-05-31 at 11.32.44 AM.png
Best,
Tong
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fsteinmetz
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Re: Polymer cloud cover and land flag

Post by fsteinmetz »

Hi Tong,

The cloud mask in Polymer is determined by a threshold on the reflectance in the NIR band, but by default it is quite relaxed to avoid masking out the sun glint (20%).
This way, the semi-transparent clouds are processed by Polymer, and water underneath still being visible.
ACOLITE has a stricter cloud mask.

Regarding the cloud mask : there is no cloud mask in OLI level1, but you can use an external cloud mask like so :

<code>
from polymer.gsw import GSW
from polymer.landsat8 import Level1_OLI
Level1_OLI(<filename>, landmask=GSW(directory=<directory_gsw_tiles>))
</code>

I hope this helps,
Cheers,
François
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