The Scene Cloud Cover score is a value that consists of the estimated percentage of cloud cover calculated over an entire Landsat scene. For scenes processed prior to Collection 1, the score is calculated using the Automatic Cloud Cover Assessment (ACCA) algorithm.
For scenes processed into Collection 1, the C Function of Mask (CFMask) algorithm is used to calculate scene cloud cover. This algorithm provides a full-image “Scene Cloud Cover” estimation, as well as a new “Land Cloud Cover” score, which is calculated only over the land pixels in a scene. The mask used to discriminate land from water is derived from the NOAA World Vector Shoreline Dataset.
Both of the Collection 1 cloud cover scores (Scene Cloud Cover and Land-Based Cloud Cover) are listed as percentages in the online metadata on EarthExplorer. Both fields are also included in the metadata (MTL.txt) file for a Collection 1 Level-1 product:
For example, if only half of image is cloud covered, while all of the land in the image is cloud covered:
CLOUD_COVER = 50.00
CLOUD_COVER_LAND = 100.00
Values are percentages (range is 0.00-100.00)