HYGEOS support forum

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? 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! Best,
Tong

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