A new parameter in the Landsat Level-1 product metadata (MTL.txt) file indicates the presence of radiometric saturation for each band in every Landsat scene:
SATURATION_BAND_8 = "N"
Related to this parameter, the Quality Assessment (QA) band for Landsat 4-5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) contains Bits 2 and 3 that represent how many bands contain saturated pixels:
11: 5 or more bands contain saturation
The saturation information provided in the MTL file and the QA band are simply an overview of saturation and do not provide band-specific saturation information at the pixel level. Pixel saturation is common for TM and ETM+ (particularly in the visible bands). Digital numbers (DN) of 255 are reserved for designating saturated pixels in TM and ETM+. Pixels surrounding those with DN values of 255 are also affected by saturation.
Features likely to cause saturation include clouds, snow/ice, barren soil, and white sand. If band-specific pixel saturation is a concern for a specific application, the DN of the Landsat Level-1 data product should be used as confirmation.