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Question:

What is the Saturation Bits parameter in the metadata file?

Answer:

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_1 = "Y"
  • SATURATION_BAND_2 = "Y"
  • SATURATION_BAND_3 = "Y"
  • SATURATION_BAND_4 = "Y"
  • SATURATION_BAND_5 = "Y"
  • SATURATION_BAND_6_VCID_1 = "Y"
  • SATURATION_BAND_6_VCID_2 = "Y"
  • SATURATION_BAND_7 = "Y"
  • 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:

  • 00:    No bands contain saturation
  • 01:     1 to 2 bands contain saturation
  • 10:     3 to 4 bands contain saturation
  • 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.