Cloud masking
From AWF-Wiki
Sentinel-2 cloud masking
The exclusion of clouds and cloud shadow is an important processing step which is usually done in an early preprocessing stage. The Sentinel-2 products are annotated with Quality Indicators (QI_DATA). In the Level 2A product you may find a file in the folder QI_DATA with the extension _CLD_20m.jp2 (data type: 8bit unsigned integer, spatial resolution 20m) which might be used for masking clouds. The data range is from 0 for high confidence clear sky to 100 for high confidence cloudy (for more details see [L2A Product Definition Document]).
