Landsat 4-7 Surface Reflectance Quality Assessment

By Landsat Missions

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.	0	1	1
Cloud LEDAPS determined this pixel contains cloud.	1	2	3
Cloud Shadow LEDAPS determined this pixel contains cloud shadow.	2	4	7
Adjacent to cloud LEDAPS determined this pixel is adjacent to a cloud pixel.	3	8	15
Snow LEDAPS determined this pixel contains snow.	4	16	31
Water LEDAPS determined this pixel is either land or water.	5	32	63
Unused	6	64	127
Unused	7	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.