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Landsat Collection 1 Level-1 Quality Assessment Band

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The Landsat Collection 1 Level-1 Quality Assessment (QA) band allows users to apply per pixel filters to the Landsat 4-5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 Operational Land Imager (OLI)-only and Landsat 8 OLI/Thermal Infrared Sensor (OLI/TIRS)- combined Collection 1 Level-1 data products. The Landsat 8 TIRS-only QA band only contains fill information.

The Pre-Collection Landsat 8 QA band page provides information on Pre-Collection Landsat 8 data.

Each pixel in the QA band contains unsigned integers that represent bit-packed combinations of surface, atmospheric, and sensor conditions that can affect the overall usefulness of a given pixel.

The tables below display the Landsat 4-5 TM, Landsat 7 ETM+, Landsat 8 OLI-only, and Landsat 8 OLI/TIRS combined Collection 1 Level-1 Quality Band attributes.

Landsat 4-5-7-8 Collection 1 Quality Band Attributes

What are QA Bits?

The bit-packed information in the QA bands is a translation of binary strings. As a simple example, the integer value “1” translates to the binary value “0001.” The binary value “0001” has 4 bits, 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 may be used to identify fill values, Bit 1 may be used to identify a dropped pixel (Landsat 4-5 TM, 7 ETM+) or terrain occlusion (Landsat 8 OLI, OLI/TIRS), Bits 2 and 3 together may be used to indicate the level of radiometric saturation present. If the condition is true, the bit is set to “1,” and “0” if false.

Used effectively, QA bits improve the integrity of science investigations by indicating which pixels might be affected by instrument artifacts or subject to cloud contamination. For example, NDVI calculated over pixels containing clouds will show anomalous values. If such pixels were included in a phenology study, the results might not show the true characteristics of seasonal vegetation growth. Cloud contaminated pixels will lower NDVI values, and measures like the timing of ‘green up’ or peak maturity would appear later than they actually occurred. A worse consequence would be that the reported reduction of vegetation growth would be taken as an indicator of environmental change, potentially prompting unnecessary land management policies or practices.

Extracting QA Band bits

The Landsat QA Tools can be used to extract bits from Landsat QA bands and the Landsat QA ArcGIS Toolbox can be used to classify, visualize, and interpret QA bit values.

Landsat Collection 1 Level-1 QA Band File (BQA.TIF)

The Landsat Collection 1 Level-1 QA band is included in the “Level-1 GeoTIFF Data Product” download option for each result on EarthExplorer.
Rigorous science applications seeking to optimize the value of pixels used in a study will find QA bits useful as a first level indicator of certain conditions.
The Collection 1 Level-1 QA image can be stretched to emphasize the light and dark pixels for a quick look at general quality conditions. In the image below, the lighter pixels are likely to be affected by a quality condition, in this case, clouds and cloud shadows. The dark areas indicate clear conditions.  Although this enables a quick “qualitative” assessment, users are encouraged to use the common pixel values (table below) to interpret the values, or use the Landsat QA Tools to extract specific QA bits that may impact quantitative image analyses for their particular studies, or use the Landsat QA ArcGIS Toolbox for visualization and interpretation of QA bit values.

Landat Collection 1 Quality Assessment Band (BQA.TIF) displayed as .jpg for reference only
Landsat Collection 1 Level-1 Quality Assessment Band (BQA.TIF) displayed as .jpg for reference only. Landsat 5 Thematic Mapper (TM) Path 39 Row 37, acquired April 26, 2012.

The pixel values in the QA file must be translated to 16-bit binary form to be used effectively.
The tables below show the bits currently populated in the Landsat 4-5 TM, Landsat 7 ETM+, and Landsat 8 OLI and OLI/TIRS Collection 1 Level-1 QA bands.

Collection 1 Landat 4-5-7-8 Quality Assessment band bits

For the single bits (0, 1, and 4):

  • 0 = "No" = This condition does not exist
  • 1 = "Yes" = This condition exists

For radiometric saturation bits (2-3), read from left to right, represent how many bands contain saturation:

  • 00 - No bands contain saturation
  • 01 - 1-2 bands contain saturation
  • 10 - 3-4 bands contain saturation
  • 11 - 5 or more bands contain saturation

For the remaining double bits (5-6, 7-8, 9-10, 11-12), read from left to right, represent levels of confidence that a condition exists:

  • 00 = “Not Determined” = Algorithm did not determine the status of this condition / "No" = This condition does not exist
  • 01 = “Low” = Algorithm has low to no confidence that this condition exists (0-33 percent confidence)
  • 10 = “Medium” = Algorithm has medium confidence that this condition exists (34-66 percent confidence)
  • 11 = “High” = Algorithm has high confidence that this condition exists (67-100 percent confidence

 

All possible pixel values and their meanings are included in the tables below.

Landsat 4-7 Collection 1 QA Values

Attribute Pixel Value
Fill 1
Dropped Pixel 2, 674
Clear 672, 676, 680, 684
Radiometric Saturation - 1-2 bands 676, 708, 756, 932, 964, 1700, 1732
Radiometric Saturation - 3-4 bands 680, 712, 760, 936, 968, 1704, 1736
Radiometric Saturation - 5+ bands 684, 716, 764, 940, 972, 1708, 1740
Cloud 752, 756, 760, 764
Cloud Confidence - Low 672, 674, 676, 680, 684, 928, 932, 936, 940, 1696, 1700, 1704, 1708
Cloud Confidence - Medium 704, 708, 712, 716, 960, 964, 968, 972, 1728, 1732, 1736, 1740
Cloud Confidence - High 752, 756, 760, 764
Cloud Shadow - High 928, 932, 936, 940, 960, 964, 968, 972
Snow/Ice - High 1696, 1700, 1704, 1708, 1728, 1732, 1736, 1740

 

Landsat 4-7 Collection 1 QA Value Interpretation

This table shows examples from the full list of possible QA values. This .xls file contains all possible Landsat 4-7 QA values and their descriptions.

Pixel Value Snow/Ice Confidence Cloud Shadow Confidence Cloud Confidence Cloud Radiometric Saturation Dropped Pixel Fill Pixel Description
0 Not Determined Not Determined Not Determined Not Determined Not Determined Not Determined Not Determined Not Determined
1 Not Determined Not Determined Not Determined Not Determined Not Determined Not Determined Yes Fill
2 Not Determined Not Determined Not Determined Not Determined Not Determined Yes No Dropped pixel
672 Low Low Low No No No No Clear terrain
674 Low Low Low No No Yes No Dropped pixel
676 Low Low Low No 1-2 bands No No Clear terrain w/ some saturation
680 Low Low Low No 3-4 bands No No Clear terrain w/ moderate saturation
684 Low Low Low No 5+ bands No No Clear terrain w/ frequent saturation
704 Low Low Medium No No No No Medium confidence cloud
1696 High Low Low No No No No Snow/Ice
1700 High Low Low No 1-2 bands No No Snow/Ice w/ some saturation

 

Landsat 8 Collection 1 QA Values

Attribute Pixel Value
Fill 1
Terrain Occlusion 2, 2722
Clear 2720, 2724, 2728, 2732
Radiometric Saturation - 1-2 bands 2724, 2756, 2804, 2980, 3012, 3748, 3780, 6820, 6852, 6900, 7076, 7108, 7844, 7876
Radiometric Saturation - 3-4 bands 2728, 2760, 2808, 2984, 3016, 3752, 3784, 6824, 6856, 6904, 7080, 7112, 7848, 7880
Radiometric Saturation - 5+ bands 2732, 2764, 2812, 2988, 3020, 3756, 3788, 6828, 6860, 6908, 7084, 7116, 7852, 7884
Cloud 2800, 2804, 2808, 2812, 6896, 6900, 6904, 6908
Cloud Confidence - Low 2720, 2722, 2724, 2728, 2732, 2976, 2980, 2984, 2988, 3744, 3748, 3752, 3756, 6816, 6820, 6824, 6828, 7072, 7076, 7080, 7084, 7840, 7844, 7848, 7852
Cloud Confidence - Medium 2752, 2756, 2760, 2764, 3008, 3012, 3016, 3020, 3776, 3780, 3784, 3788, 6848, 6852, 6856, 6860, 7104, 7108, 7112, 7116, 7872, 7876, 7880, 7884
Cloud Confidence - High 2800, 2804, 2808, 2812, 6896, 6900, 6904, 6908
Cloud Shadow - High 2976, 2980, 2984, 2988, 3008, 3012, 3016, 3020, 7072, 7076, 7080, 7084, 7104, 7108, 7112, 7116
Snow/Ice - High 3744, 3748, 3752, 3756, 3776, 3780, 3784, 3788, 7840, 7844, 7848, 7852, 7872, 7876, 7880, 7884
Cirrus Confidence - Low 2720, 2722, 2724, 2728, 2732, 2752, 2756, 2760, 2764, 2800, 2804, 2804, 2808, 2812, 2976, 2980, 2984, 2988, 3008, 3012, 3016, 3020, 3744, 3748, 3752, 3756, 3780, 3784, 3788
Cirrus Confidence - High 6816, 6820, 6824, 6828, 6848, 6852, 6856, 6860, 6896, 6900, 6904, 6908, 7072, 7076, 7080, 7084, 7104, 7108, 7112, 7116, 7840, 7844, 7848, 7852, 7872, 7876, 7880, 7884

 

Landsat 8 Collection 1 QA Value Interpretation

This table shows examples from the full list of possible QA values. This .xls file contains all possible Landsat 8 QA values and their descriptions.

Pixel Value Cirrus Confidence Snow/Ice Confidence Cloud Shadow Confidence Cloud Confidence Cloud Radiometric Saturation Terrain Occlusion Fill Pixel Description
0

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not determined

1

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Yes

Fill

2

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Not Determined

Yes

No

Terrain occlusion

2720

Low

Low

Low

Low

No

No

No

No

Clear terrain

2804

Low

Low

Low

High

Yes

1-2 bands

No

No

High confidence cloud with some saturation

2988

Low

Low

High

Low

No

5+ bands

No

No

Cloud shadow with frequent saturation

3744

Low

High

Low

Low

No

No

No

No

Snow/ice

3748

Low

High

Low

Low

No

1-2 bands

No

No

Snow/ice with some saturation

7072

High

Low

High

Low

No

No

No

No

Cirrus cloud, cloud shadow

7076

High

Low

High

Low

No

1-2 bands

No

No

Cirrus cloud, cloud shadow with some saturation

7116

High

Low

High

Medium

No

5+ bands

No

No

Cirrus cloud, cloud shadow, medium cloud confidence with frequent saturation

For assistance with unpacking the Quality Assessment band, check out the Landsat QA Tools or the Landsat QA ArcGIS Toolbox.

Collection 1 LandsatLook 8-bit Quality Image

The Collection 1 LandsatLook 8-bit Quality Image (.jpg) provides a quick view of the quality of the pixels within the scene to determine if a particular scene would work best for the user's application. LandsatLook Collection 1 Quality images can be downloaded individually from the Download Options for each Landsat Level-1 result using EarthExplorer (EE).

The tables below display the values and colors associated with the Collection 1 LandsatLook 8-bit Quality Images. 

Collection 1 LandsatLook Quality Assessment Image Bit Values

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