HYGEOS support forum

Hello, I'm Minsun Lee, a beginner polymer user.

Thank you for the great working polymer!

I have a question about its flag.
When I displayed each flag, 256 is missing, and 1 and 2 do not look like land and cloud, respectively.
Could I get some advice if I'm using the flag correctly?
Attached is the example, Sentinel-2B 2021-11-06, Chesapeake Bay

Thank you!

Dear Minsun Lee,

Thanks for your message ! Yes it seems you are using the flags correctly. To answer your questions :
- 256 is not used, it is a placeholder - no problem about that.
- 1 is missing because there is no land mask in Sentinel 2 level1 products. To apply a land mask, you can use GSW by passing a GSW object to Level1_MSI(..., landmask=GSW(...)). In this case it will fill the LAND flag.
- CLOUD_BASE looks more like land, because since the land mask is missing, the cloud mask triggers above all bright surface, which is what you see here.
I hope this helps.
Cheers,
François