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How do I use Quality Assessment (QA) bands that are delivered with Landsat products?

Some Landsat products include Quality Assessment (QA) bands with unsigned integers that represent bit-packed information for each pixel. Details for individual products are at: 

These files must be unpacked to a binary form to be used effectively. The bit-packed information in a QA band is a decimal translation of binary strings. For example, the decimal value “1” translates to the binary value “0001.” The binary value “0001” has 4 bits (0, 1, 2, and 3), written right to left as bits 0 (“1”), 1 (“0”), 2 (“0”), and 3 (“0”).  

Each of the bits 0-3 represents a condition that can affect the calculation of a physical value:  

  • Bit 0 can be used to identify fill values 
  • Bit 1 can be used to identify a cloud 
  • Bit 2 can be used to indicate water 
  • Bit 3 can be used identify snow 

If the condition is true, the bit is set to “1”; if the condition is false, the bit is set to “0”:  

  • Bit 0 = 1 = fill  
  • Bit 1 = 0 = no cloud  
  • Bit 2 = 0 = land  
  • Bit 3 = 0 = no snow 

Quality Assessment tools are available to help users classify and extract bit packed values to enhance interpretation of the QA values for all Landsat data products. 

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