Landsat Missions

Landsat Collection 1 Level-1 Quality Assessment Band

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Landsat Collection 1 Level-1 Quality Assessment (QA) provides useful information to users wanting to optimize the value of pixels as a first level indicator of certain conditions within Landsat 8 Operational Land Imager (OLI), Landsat 8 OLI-Thermal Infrared Sensor (TIRS), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 4-5 Thematic Mapper (TM), and Landsat 1-5 Multispectral Scanner (MSS) Level-1 data. 

There are two QA related files available for all Landsat 1-8 data products: the Landsat Collection 1 LandsatLook 8-bit Quality Image, and the Landsat Collection 1 Level-1 Quality Assessment (QA) 16-bit Band. These quality attributes vary between Landsat sensors and are described respectively below. 

Landsat Collection 1 LandsatLook 8-bit Quality Image

The Landsat Collection 1 LandsatLook 8-bit Quality Image provides a description of the quality of the pixels within a scene that may help the user determine its suitability for application. LandsatLook Collection 1 Quality images (.jpg) can be downloaded individually from the Download Options window for the results of each Landsat Collection 1 Level-1 dataset in EarthExplorer

Landsat Collection 1 LandsatLook 8-bit Quality Image Designations
Landsat 8 OLI/TIRS Landsat 7 ETM+, Landsat 4-5 TM Landsat 1-5 MSS Color
Bit Description Bit Description Bit Description  
0 Designated Fill 0 Designated Fill 0 Designated Fill

 

1 Terrain Occlusion 1 Dropped Pixel 1 Dropped Pixel 

 

2 Radiometric Saturation  2 Radiometric Saturation  2 Radiometric Saturation 

 

3 Cloud 3 Cloud 3 Cloud

 

4 Cloud Shadow 4 Cloud Shadow  4 Unused

 

5 Snow/Ice  5 Snow/Ice  5 Unused

 

6 Cirrus  6 Unused 6 Unused

 

7 Unused 7 Unused 7 Unused

Unused

Table 1. Landsat Collection 1 LandsatLook 8-bit Quality Image Designations 

Landsat Collection 1 Level-1 Quality Assessment (QA) 16-bit Band

The Landsat Collection 1 Level-1 Quality Assessment (QA) 16-bit band allows users to apply per pixel filters to all Landsat Collection 1 Level-1 data products. 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. Landsat Collection 1 Level-1 QA bands (.TIF) are included in the Landsat Level-1 GeoTIFF Data Product downloaded from EarthExplorer.* Descriptions of each QA bit and pixel values are provided below.

*Landsat 8 OLI-only products contain all QA bits; Landsat 8 TIRS-only products contain only fill information. 

The Collection 1 Level-1 QA band can be stretched to emphasize the light and dark pixels for an immediate survey of a scene's general quality conditions. For example, in the image below, the bright white pixels are likely to be affected by a quality condition, in this case, clouds and cloud shadows. The dark areas indicate clear conditions.  

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

Although this enables a quick “qualitative” assessment of a scene, users are encouraged to use the common pixel values (table below) to interpret the bit 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 to classify, visualize, and interpret Level-1 QA bit values.

What are QA Bits?

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

Used effectively, QA bits help improve the integrity of Landsat-derived science investigations by indicating which pixels might be affected by surface conditions, cloud contamination, or sensor conditions. 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 surface 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. 

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

Landsat 1-8 Collection 1 Level-1 Quality Bit Designations
Figure 2. Landsat 1-8 Collection 1 Level-1 Quality Bit Designations

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


Landsat 8 OLI/ OLI-TIRS Level-1 Possible Attributes, Pixel Values, and Pixel Value Interpretations

The tables below display the attributes and pixel values,and examples from the full list of possible QA values and interpretations for Landsat 8 OLI and OLI/TIRS Level-1 data. 

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

Table 2. Landsat 8 OLI, OLI/TIRS Level-1 Possible Attributes and Pixel Values

 

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

Table 3. Landsat 8 Collection 1 Level-1 QA Value Interpretations (This .xls file contains all possible combinations of Landsat 8 QA values and their descriptions)

 

Landsat 4-5 TM, Landsat 7 ETM+ Level-1 Possible Attributes, Pixel Values, and Pixel Value Interpretations

The tables below display the attributes and pixel values,and examples from the full list of possible QA values and interpretations for Landsat 4-5 TM and Landsat 7 ETM+ Level-1 data.  

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

Table 4. Landsat 4-5 TM, Landsat 7 ETM+ Level-1 Possible Attributes and Pixel Values

 

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

Table 5. Landsat 4-7 Collection 1 Level-1 QA Value Interpretation (This.xls file contains all possible combinations of Landsat 4-7 QA values and their descriptions)

 

Landsat 1-5 MSS Collection 1 Level-1 Possible Attributes,Pixel Values, and Pixel Value Interpretations

The tables below display the attributes and pixel values,and examples from the full list of possible QA values and interpretations for Landsat 1-5 MSS Level-1 data.  

Attribute Pixel Value
Fill 1
Dropped Pixel 2, 34
Clear 32, 36, 40, 44
Radiometric Saturation - 1-2 bands 34, 36, 68, 116
Radiometric Saturation - 3-4 bands 40, 72, 120
Radiometric Saturation - 5+ bands 44, 76, 124
Cloud 112, 116, 120, 124
Cloud Confidence - Low 32, 34, 36, 40, 44
Cloud Confidence - Medium 64, 68, 72, 76
Cloud Confidence - High 112, 116, 120, 124

Table 6. Landsat 1-5 MSS Level-1 Possible Attributes and Pixel Values

 

Pixel Value Cloud Confidence Cloud Radiometric Saturation Dropped Pixel Fill Pixel Description
0 Not Determined Not Determined Not Determined Not Determined Not Determined Not Determined
1 Not Determined Not Determined Not Determined Not Determined Yes Fill
2 Not Determined Not Determined Not Determined Yes No Dropped pixel
32 Low No No No No Clear terrain
34 Low No Not Determined Yes No Dropped pixel w/ clear terrain
36 Low No 1-2 bands No No Clear terrain w/ some saturation
40 Low No 3-4 bands No No Clear terrain w/ moderate saturation
44 Low No 5+ bands No No Clear terrain w/ frequent saturation
64 High Yes No No No Medium confidence cloud
68 Medium No 1-2 bands No No Medium confidence cloud w/ some saturation
72 Medium No 3-4 bands No No Medium confidence cloud w/ moderate saturation
76 Medium No 5+ bands No No Medium confidence cloud w/frequent saturation
112 High Yes No No No Cloud
116 High Yes 1-2 bands No No Cloud w/ some saturation
120 High Yes 3-4 bands No No Cloud w/ moderate saturation
124 High Yes 5+ bands No No Cloud w/ frequent saturation

Table 7. Landsat 1-5 MSS  Collection 1 Level-1 QA Value Interpretation

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