Landsat Missions

Landsat Surface Reflectance Quality Assessment

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Landsat Surface Reflectance products include Quality Assessment (QA) bands to identify the pixels that exhibit adverse instrument, atmospheric, or surficial conditions.  Used effectively, QA information improves 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 would likely 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 the reported reduction of vegetation growth would be taken as an indicator of environmental change, potentially prompting unnecessary land management policies or practices.

NOTE: Landsat 4-5 Thematic Mapper (TM) or Landsat 7 Enhanced Thematic Mapper Plus (ETM+) Surface Reflectance products are generated from the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS).  Landsat 8 Surface Reflectance data are generated from the Landsat Surface Reflectance Code (LaSRC). The differences between these algorithms can be found on the Landsat Surface Reflectance Level-2 Data Products webpage.  Details on how each algorithm assesses quality conditions are described below.

Landsat 4-5 TM / Landsat 7 ETM+ Surface Reflectance (LEDAPS)

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.

sr_cloud_qa band
  • 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.
  • Snow – LEDAPS determined this pixel contains snow.
  • Land/Water – LEDAPS determined this pixel is either land or water.
  • Adjacent Cloud – LEDAPS determined this pixel is adjacent to a cloud pixel.

sr_atmos_opacity band

  • Atmospheric Opacity – LEDAPS derives an estimation of atmospheric contamination in a given pixel.

pixel_qa band

  • Pixel QA – This alternative quality assessment algorithm, containing cloud, cloud confidence, cloud shadow, snow/ice and water, is generated by the CFMask algorithm and is likely to present more accurate results than its companion LEDAPS bands for cloud, cloud shadow, snow, and water identification.

radsat_qa band

  • Radiometric Saturation – This band is a bit-packed representation of which sensor bands were saturated during data capture, yielding unusable data.

 

sr_cloud_qa

 

LEDAPS’ quality conditions are expressed as either true or false, and are stored in a bit_packed file named sr_cloud_qa. The table below describes the sr_cloud_qa band’s attributes.

Bit Bit Value Cumulative Sum Attribute
0 1 1 Dark Dense Vegetation (DDV)
1 2 3 Cloud
2 4 7 Cloud Shadow
3 8 15 Adjacent to cloud
4 16 31 Snow
5 32 63 Water
6 64 127 Unused
7 128 255 Unused

Table 1. Landsat 4-7 Surface Reflectance Cloud Quality Assessment (sr_cloud_qa) band attributes.

The table below provides the values of the Landsat 4-7 sr_cloud_qa band.

Attribute  Pixel Value
DDV 1, 9
Cloud 2, 34
Cloud Shadow 4, 12, 20, 36, 52
Adjacent to cloud 8, 12, 24, 40, 56
Snow 16, 20, 24, 48, 52, 56
Water 32, 34, 36, 40, 48, 52, 56

Table 2. Landsat 4-7 Surface Reflectance Cloud Quality Assessment (sr_cloud_qa) band values.

The table below provides the bit value interpretation of the Landsat 4-7 sr_cloud_qa band.

Pixel Value DDV Cloud Cloud Shadow Adjacent to cloud Snow Water Pixel Description
0 No No No No No No None
1 Yes No No No No No DDV
2 No Yes No No No No Cloud
4 No No Yes No No No Cloud shadow
8 No No No Yes No No Adjacent to cloud
9 Yes No No Yes No No DDV, adjacent to cloud
12 No No Yes Yes No No Adjacent to cloud, cloud shadow
16 No No No No Yes No Snow
20 No No Yes No Yes No Cloud shadow, snow
24 No No No Yes Yes No Adjacent to cloud, snow
32 No No No No No Yes Water
34 No Yes No No No Yes Cloud, water
36 No No Yes No No Yes Cloud shadow, water
40 No No No Yes No Yes Adjacent to cloud, water
48 No No No No  Yes Yes Snow, water
52 No No Yes No Yes Yes Cloud shadow, snow, water
56 No No No Yes Yes Yes Adjacent to cloud, snow, water

Table 3. Landsat 4-7 Surface Reflectance Cloud Quality Assessment (sr_cloud_qa) band values interpretation.

sr_atmos_opacity

Additionally, an atmospheric opacity band, sr_atmos_opacity, is derived during LEDAPS processing, which is an estimation of atmospheric contamination in a given pixel. The table below describes the sr_atmos_opacity band’s attributes.

Band Designation Band Name Units Range Valid Range Fill Value Saturate Value Scale Factor
sr_atmos_opacity Atmospheric
Opacity
Unitless -2000 - 16000 0 - 10000 -9999 NA 0.0010

Table 4. Landsat 4-7 Surface Reflectance Atmospheric Opacity (sr_atmos_opacity) band attributes.

General interpretation for atmospheric opacity:

  • < 0.1 = clear
  • 0.1 - 0.3 = average
  • > 0.3 = hazy

pixel_qa

The Pixel QA band’s quality conditions are expressed as a confidence level or as either true or false, and are stored in a bit-packed file named pixel_qa. The table below describes the pixel_qa band’s attributes:

Bit Bit Value Cumulative Sum Attribute
0 1 1 Fill
1 2 3 Clear
2 4 7 Water
3 8 15 Cloud Shadow
4 16 31 Snow
5 32 63 Cloud
6 64 127 Cloud Confidence
00 = none
01 = low
10 = medium
11 = high
7 128 255
8 256 511 Unused
9 512 1023 Unused
10 1024 2047 Unused
11 2048 4095 Unused
12 4096 8191 Unused
13 8192 16383 Unused
14 16384 32767 Unused
15 32786 65553 Unused

Table 5. Landsat 4-7 Surface Reflectance Pixel Quality Assessment (pixel_qa) band attributes.

The table below provides the values of the Landsat 4-7 pixel_qa band.

Attribute  Pixel Value
Fill 1
Clear 66, 130
Water 68, 132
Cloud Shadow 72, 136
Snow/Ice 80, 112, 144, 176
Cloud 96, 112, 160, 176, 224
Low cloud confidence 66, 68, 72, 80, 96, 112
Medium cloud confidence 130, 132, 136, 144, 160, 176
High cloud confidence 224

Table 6. Landsat 4-7 Surface Reflectance Pixel Quality Assessment (pixel_qa) band values.

The table below provides the bit value interpretation of the Landsat 4-7 pixel_qa band.

Pixel Value Fill Clear Water Cloud Shadow Snow Cloud Cloud Confidence Pixel Description
1 Yes No No No No No None Fill pixel
66 No Yes No No No No Low Clear, low-confidence cloud
68 No No Yes No No No Low Water, low-confidence cloud
72 No No No Yes No No Low Cloud shadow, low-confidence cloud
80 No No No No Yes No Low Snow/ice, low-confidence cloud
96 No No No No No Yes Low Cloud, low-confidence cloud
112 No No No No Yes Yes Low Snow/ice, cloud, low-confience cloud
130 No Yes No No No No Medium Clear, medium-confidence cloud
132 No No Yes No No No Medium Water, medium-confidence cloud
136 No No No Yes No No Medium Cloud shadow, medium-confidence cloud
144 No No No No Yes No Medium Snow/ice, medium-confidence cloud
160 No No No No No Yes Medium Cloud, medium-confidence cloud
176 No No No No Yes Yes Medium Snow/ice, cloud, medium-confidence cloud
224 No No No No No Yes High Cloud, high-confidence cloud

Table 7. Landsat 4-7 Surface Reflectance Pixel Quality Assessment (pixel_qa) band bit value interpretation.

radsat_qa

The Radiometric Saturation band's quality conditions are expressed as either true or false and are stored in a bit-packed file, named radsat_qa. The table below describes the radsat_qa band's attributes.

Bit Bit Value Cumulative Sum Description
Bits are numbered from right to left (bit 1 = LSB, bit 7 = MSB)
0 1 1 Data Fill Flag (0 valid data, 1 invalid data)
1 2 3 Band 1 Data Saturation Flag (0 valid data, 1 saturated data)
2 4 7 Band 2 Data Saturation Flag (0 valid data, 1 saturated data)
3 8 15 Band 3 Data Saturation Flag (0 valid data, 1 saturated data)
4 16 31 Band 4 Data Saturation Flag (0 valid data, 1 saturated data)
5 32 63 Band 5 Data Saturation Flag (0 valid data, 1 saturated data)
6 64 127 Band 6 Data Saturation Flag (0 valid data, 1 saturated data)
7 128 255 Band 7 Data Saturation Flag (0 valid data, 1 saturated data)

Table 8. Landsat 4-7 Surface Reflectance Radiometric Saturation Quality Assessment (radsat_qa) band attributes.

Landsat 8 OLI/TIRS Surface Reflectance (LaSRC)

During Landsat 8 OLI/TIRS Surface Reflectance generation, LaSRC assesses the following quality conditions and expresses them using the bands described below.

sr_aerosol band
  • Fill – There are no data values in this pixel.    
  • Aerosol Retrieval – The retrieval of aerosol measurements was valid in this pixel.
  • Water – LaSRC identified this pixel as water.
  • Cloud or Cirrus - LaSRC identified this pixel as cloud or cirrus cloud.
  • Cloud shadow - LaSRC identified this pixel as cloud shadow.
  • Aerosol Retrieval - The retrieval of aerosol measurements was invalid and interpolated from nearby observations.
  • Aerosol Content – LaSRC determined the amount of aerosol in this pixel to be climatology-grade, low, medium, or high.
pixel_qa band
  • Pixel QA – This alternative quality assessment algorithm, containing cloud, cloud confidence, cirrus cloud confidence, cloud shadow, snow/ice and water, is generated by the CFMask algorithm and is likely to present more accurate results than the internal tests LaSRC uses for cloud, cloud shadow, snow/ice and water.
radsat_qa band
  • Radiometric Saturation – This band is a bit-packed representation of which sensor bands were saturated during data capture, yielding unusable data.

sr_aerosol

 

LaSRC’s quality conditions are expressed as a confidence level or as either true or false, and are stored in a bit_packed file named sr_aerosol. The table below describes the sr_aerosol band's attributes.

Bit Bit Value Cumulative Sum Attribute
0 1 1 Fill Value
1 2 3 Valid Aerosol Retrieval
2 4 7 Water Pixel (or water pixel was used in the fill-the-window interpolation)
3 8 15 Cloud or Cirrus
4 16 31 Cloud Shadow
5 32 63 Non-center window pixel for which aerosol was interpolated from surrounding NxN center pixels
6 64 127 Aerosol Content
00 - Climatology
01 - Low
10 - Medium
11 - High
7 128 255

Table 9. Landsat 8 Surface Reflectance Aerosol Quality Assessment (sr_aerosol) band attributes.

The table below provides the values of the Landsat 8 sr_aerosol band.

Attribute Pixel Value
Fill 1
Valid Aerosol Retrieval 2, 66, 130, 194
Water Pixel (or water pixel was used
in the fill-the-window interpolation)
4, 68, 100, 132, 164, 196, 228
Cloud or Cirrus 8, 72, 136, 200
Cloud Shadow 16, 80, 144, 208
Non-center window pixel for which aerosol was
interpolated from surrounding NxN center pixels
32, 96, 100, 160, 164, 224, 228
Low-level Aerosol 66, 68, 72, 80, 96, 100
Medium-level Aerosol 130, 132, 136, 144, 160, 164
High-level Aerosol 194, 196, 200, 208, 224, 228

Table 10. Landsat 8 Surface Reflectance Aerosol Quality Assessment (sr_aerosol) band values.

The table below provides the bit value interpretation of the Landsat 8 sr_aerosol band.

Pixel Value Fill Valid Aerosol Water Cloud/Cirrus Cloud Shadow Interpolated Aerosol Aerosol Pixel Description
1 Yes No No No No No N/A Fill
2 No Yes No No No No Climatology Valid aerosol retrieval
4 No No Yes No No No Climatology Water
8 No No No Yes No No Climatology Cloud/cirrus
16 No No No No Yes No Climatology Cloud shadow
32 No No No No No Yes Climatology Interpolated aerosol
66 No Yes No No No No Low Valid aerosol retrieval, low aerosol
68 No No Yes No No No Low Water, low aerosol
72 No No No Yes No No Low Cloud/cirrus, low aerosol
80 No No No No Yes No Low Cloud shadow, low aerosol
96 No No No No No Yes Low Interpolated aerosol, low aerosol
100 No No Yes No No Yes Low Water pixel used in interpolation,
interpolated aerosol, low aerosol
130 No Yes No No No No Medium Valid aerosol, medium aerosol
132 No No Yes No No No Medium Water, medium aerosol
136 No No No Yes No No Medium Cloud/cirrus, medium aerosol
144 No No No No Yes No Medium Cloud shadow, medium aerosol
160 No No No No No Yes Medium Interpolated aerosol, medium aerosol
164 No No Yes No No Yes Medium Water pixel used in interpolation,
interpolated aerosol, medium aerosol
194 No Yes No No No No High Valid aerosol, high aerosol
196 No No Yes No No No High Water, high aerosol
200 No No No Yes No No High Cloud/cirrus, high aerosol
208 No No No No Yes No High Cloud shadow, high aerosol
224 No No No No No Yes High Interpolated aerosol, high aerosol
228 No No Yes No No Yes High Water pixel used in interpolation,
interpolated aerosol, high aerosol

Table 11. Landsat 8 Surface Reflectance Aerosol Quality Assessment (sr_aerosol) band values interpretations.

pixel_qa

The Pixel QA band’s quality conditions are expressed as a confidence level or as either true or false, and are stored in a bit-packed file named pixel_qa. The table below describes the pixel_qa band’s attributes.

Bit Bit Value Cumulative Sum Attribute
0 1 1 Fill
1 2 3 Clear
2 4 7 Water
3 8 15 Cloud Shadow
4 16 31 Snow
5 32 63 Cloud
6 64 127 Cloud Confidence
00 = none
01 = low
10 = medium
11 = high
7 128 255
8 256 511 Cirrus Confidence
00 = not set
01 = low from OLI band 9 reflectance
10 = medium from OLI band 9 reflectance
11 = high from OLI band 9 reflectance
9 512 1023
10 1024 2047 Terrain Occlusion
11 2048 4095 Unused
12 4096 8191 Unused
13 8192 16383 Unused
14 16384 32767 Unused
15 32786 65553 Unused

Table 12. Landsat 8 Surface Reflectance Pixel Quality Assessment (pixel_qa) band attributes.

The table below provides the values of the Landsat 8 pixel_qa band.

Attribute Pixel Value
Fill 1
Clear 322, 386, 834, 898, 1346
Water 324, 388, 836, 900, 1348
Cloud Shadow 328, 392, 840, 904, 1350
Snow/Ice 336, 368, 400, 432, 848, 880, 912, 944, 1352
Cloud 352, 368, 416, 432, 480, 864, 880, 928, 944, 992
Low confidence cloud 322, 324, 328, 336, 352, 368, 834, 836, 840, 848, 864, 880
Medium confidence cloud 386, 388, 392, 400, 416, 432, 900, 904, 928, 944
High confidence cloud 480, 992
Low confidence cirrus 322, 324, 328, 336, 352, 368, 386, 388, 392, 400, 416, 432, 480
High confidence cirrus 834, 836, 840, 848, 864, 880, 898, 900, 904, 912, 928, 944, 992
Terrain occlusion 1346, 1348, 1350, 1352

Table 13. Landsat 8 Surface Reflectance Pixel Quality Assessment (pixel_qa) band values.

The table below provides the bit value interpretation of the Landsat 8 pixel_qa band.

Pixel Value Fill Clear Water Cloud Shadow Snow/Ice Cloud Cloud Confidence Cirrus Confidence Terrain Occlusion Pixel Description
1 Yes No No No No No None None No Fill
322 No Yes No No No No Low Low No Clear terrain, low confidence cloud, low confidence cirrus
324 No No Yes No No No Low Low No Water, low confidence cloud, low confidence cirrus
328 No No No Yes No No Low Low No Cloud shadow, low confidence cloud, low confidence cirrus
336 No No No No Yes No Low Low No Snow/Ice, low confidence cloud, low confidence cirrus
352 No No No No No Yes Low Low No Cloud, low confidence cloud, low confidence cirrus
368 No No No No Yes Yes Low Low No Snow/Ice, cloud, low confidence cloud, low confidence cirrus
386 No Yes No No No No Medium Low No Clear terrain, medium confidence cloud, low confidence cirrus
388 No No Yes No No No Medium Low No Water, medium confidence cloud, low confidence cirrus
392 No No No Yes No No Medium Low No Cloud shadow, medium confidence cloud, low confidence cirrus
400 No No No No Yes No Medium Low No Snow/Ice, medium confidence cloud, low confidence cirrus
416 No No No No No Yes Medium Low No Cloud, medium confidence cloud, low confidence cirrus
432 No No No No Yes Yes Medium Low No Snow/Ice, cloud, medium confidence cloud, low confidence cirrus
480 No No No No No Yes High Low No Cloud, high confidence cloud, low confidence cirrus
834 No Yes No No No No Low High No Clear terrain, low confidence cloud, high confidence cirrus
836 No No Yes No No No Low High No Water, low confidence cloud, high confidence cirrus
840 No No No Yes No No Low High No Cloud shadow, low confidence cloud, high confidence cirrus
848 No No No No Yes No Low High No Snow/Ice, low confidence cloud, high confidence cirrus
864 No No No No No Yes Low High No Cloud, low confidence cloud, high confidence cirrus
880 No No No No Yes Yes Low High No Snow/Ice, cloud, low confidence cloud, high confidence cirrus
898 No Yes No No No No Medium High No Clear terrain, medium confidence cloud, high confidence cirrus
900 No No Yes No No No Medium High No Water, medium confidence cloud, high confidence cirrus
904 No No No Yes No No Medium High No Cloud shadow, medium confidence cloud, high confidence cirrus
912 No No No No Yes No Medium High No Snow/Ice, medium confidence cloud, high confidence cirrus
928 No No No No No Yes Medium High No Cloud, medium confidence cloud, high confidence cirrus
944 No No No No Yes Yes Medium High No Snow/Ice, cloud, medium confidence cloud, high confidence cirrus
992 No No No No No Yes High High No Cloud, high confidence cloud, high confidence cirrus
1346 No Yes No No No No Low Low Yes Clear terrain, terrain occluded
1348 No No Yes No No No Low Low Yes Water, terrain occluded
1350 No No No Yes No No Low Low Yes Cloud shadow, terrain occluded
1352 No No No No Yes No Low Low Yes Snow/ice, terrain occluded

Table 14. Landsat 8 Surface Reflectance Pixel Quality Assessment (pixel_qa) band values interpretation.

radsat_qa

The Radiometric Saturation band's quality conditions are expressed as either true or false, and are stored in a bit-packed file, named radsat_qa. The table below describes the radsat_qa band's attributes.

Bit Bit Value Cumulative Sum Description
Bits are numbered from right to left (bit 1 = LSB, bit 11 = MSB)
0 1 1 Data Fill Flag (0 valid data, 1 invalid data)
1 2 3 Band 1 Data Saturation Flag (0 valid data, 1 saturated data)
2 4 7 Band 2 Data Saturation Flag (0 valid data, 1 saturated data)
3 8 15 Band 3 Data Saturation Flag (0 valid data, 1 saturated data)
4 16 31 Band 4 Data Saturation Flag (0 valid data, 1 saturated data)
5 32 63 Band 5 Data Saturation Flag (0 valid data, 1 saturated data)
6 64 127 Band 6 Data Saturation Flag (0 valid data, 1 saturated data)
7 128 255 Band 7 Data Saturation Flag (0 valid data, 1 saturated data)
8 N/A N/A Not used
9 512 1023 Band 9 Data Saturation Flag (0 valid data, 1 saturated data)
10 1024 2047 Band 10 Data Saturation Flag (0 valid data, 1 saturated data)
11 2048 4095 Band 11 Data Saturation Flag (0 valid data, 1 saturated data)

Table 15. Landsat 8 Surface Reflectance Radiometric Saturation Quality Assessment (radsat_qa) band attributes.

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