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Landsat 4-7 Surface Reflectance Quality Assessment

Landsat 4-7 Surface Reflectance products are consistent, science-quality data and are atmospherically corrected for accurate analysis of land surface changes over time. Quality Assessment (QA) bands included with the products provide bit-packed combinations of surface, atmosphere, and sensor conditions that can affect the overall usefulness of a given pixel.

Return to Landsat Surface Reflectance Quality Assessment Overview
 

Landsat 4-7 Surface Reflectance Science Products are generated from Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) specialized software. During Landsat 4-5 TM and Landsat 7 ETM+ Surface Reflectance generation, LEDAPS assesses the following quality conditions and expresses them using the bands described below. 

Specific attributes for each band described below can be found in the Landsat 4-7 Collection 2 Level-2 Science Product Guide
 

SR_CLOUD_QA band 

LEDAPS quality conditions are expressed as either true or false and are stored in a bit-packed SR_CLOUD_QA file. The band's attributes are described in the table below. 

Attribute 

Bit 

Bit Value 

Cumulative Sum 

Dark Dense Vegetation (DDV) 
LEDAPS determined this pixel contains DDV, which is used to estimate aerosol 
optical thickness, a critical component to the atmospheric correction routine.  
The accuracy with which surface reflectance is calculated is dependent on how much DDV is available in a scene. 

Cloud 
LEDAPS determined this pixel contains cloud.

Cloud Shadow 
LEDAPS determined this pixel contains cloud shadow. 

Adjacent to cloud 
LEDAPS determined this pixel is adjacent to a cloud pixel. 

15 

Snow 
LEDAPS determined this pixel contains snow. 

16 

31 

Water
LEDAPS determined this pixel is either land or water. 

32 

63 

Unused 

64 

127 

Unused 

128 

255 

 

QA_PIXEL band 

The Pixel QA band is generated by the C Function of Mask (CFMask) algorithm and can be used as an alternative quality assessment source for pixel quality. The band is carried through unchanged from Landsat Level-1data and contains cloud, cloud confidence, cloud shadow, snow/ice and water information. Please note, the Pixel QA band is likely to present more accurate results than its companion LEDAPS bands for cloud, cloud shadow, snow, and water identification. The Pixel QA band’s quality conditions are expressed as a confidence level or as either true or false. 

 

QA_RADSAT band 

The Radiometric Saturation band's quality conditions are expressed as either true or false and are stored in the QA_RADSAT bit-packed file. This band is a representation of which sensor bands were saturated during data capture, yielding unusable data. 

 

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