NAME
i.landsat.qa - Reclassifies Landsat QA band according to acceptable pixel quality as defined by the user.
KEYWORDS
imagery,
pixel,
quality,
qa,
bitpattern,
mask,
landsat
SYNOPSIS
i.landsat.qa
i.landsat.qa --help
i.landsat.qa [output=name] [dataset=string] [designated_fill=string] [cloud=string] [cloud_confidence=string[,string,...]] [cloud_shadow_confidence=string[,string,...]] [snow_ice_confidence=string[,string,...]] [cirrus_confidence=string[,string,...]] [dilated_cloud=string] [snow=string] [clear=string] [water=string] [terrain_occlusion=string] [radiometric_saturation=string[,string,...]] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --help
- Print usage summary
- --verbose
- Verbose module output
- --quiet
- Quiet module output
- --ui
- Force launching GUI dialog
Parameters:
- output=name
- Output file with reclass rules
- dataset=string
- Landsat dataset to search for
- Options: landsat_tm_c1, landsat_etm_c1, landsat_8_c1, landsat_tm_c2_l1, landsat_tm_c2_l2, landsat_etm_c2_l1, landsat_etm_c2_l2, landsat_ot_c2_l1, landsat_ot_c2_l2
- Default: landsat_8_c1
- designated_fill=string
- Unacceptable conditions for Designated Fill
- Options: No, Yes
- cloud=string
- Unacceptable conditions for Clouds
- Options: No, Yes
- cloud_confidence=string[,string,...]
- Unacceptable conditions for Cloud confidence
- Options: Not Determined, Low, Medium, High
- cloud_shadow_confidence=string[,string,...]
- Unacceptable conditions for Cloud Shaddow Confidence
- Options: Not Determined, Low, Medium, High
- snow_ice_confidence=string[,string,...]
- Unacceptable conditions for Snow/Ice Confidence
- Options: Not Determined, Low, Medium, High
- cirrus_confidence=string[,string,...]
- Unacceptable conditions for Cirrus Confidence
- Options: Not Determined, Low, Medium, High
- dilated_cloud=string
- Unacceptable conditions for Pixels with Dilated Clouds (only collection 2)
- Options: No, Yes
- snow=string
- Unacceptable conditions for Snow Pixels (only collection 2)
- Options: No, Yes
- clear=string
- Unacceptable conditions for Clear Pixels (only collection 2)
- Options: No, Yes
- water=string
- Unacceptable conditions for Water Pixels (only collection 2)
- Options: No, Yes
- terrain_occlusion=string
- Unacceptable conditions for Terrain Occlusion / Dropped Pixels (only collection 1)
- Options: No, Yes
- radiometric_saturation=string[,string,...]
- Unacceptable conditions for Radiometric Saturation (only collection 1)
- Options: Not Determined, Low, Medium, High
Removing unreliable pixels is a fundamental and one of the first steps in
remote sensing. Landsat imagery provides a Quality Assessment (QA) band which
can be used for this purpose.
The i.landsat.qa module generates reclassification rule files which
can be used in r.reclass for filtering the
QA band according to pixel quality characteristics the user defines as
unacceptable. It works with both Collection 1 and Collection 2 data from
Landsat 8 OLI/TIRS, 4-7 TM/ETM+. The dataset the QA band belongs to
is specified like in i.landsat.download.
Values defined as unacceptable for a given condition will be set to NULL
in the output raster map. All other values will be set to 1.
The Quality Assessment (QA) band from Landsat contains 16bit integer
values that represent "bit-packed combinations of surface, atmosphere, and
sensor conditions that can affect the overall usefulness of a given pixel".
The following quality relevant conditions are represented as "single bits"
in the Landsat QA band:
Condition |
Collection |
Designated Fill |
1,2 |
Dilated Cloud |
2 |
Terrain Occlusion / Dropped Pixels |
1 |
Cloud |
1,2 |
Cirrus |
2 |
Cloud Shadow |
2 |
Snow |
2 |
Clear |
2 |
Water |
2 |
Possible choices for the "single bits" are:
Value |
Description |
Bit representation |
No |
This condition does not exist |
0 |
Yes |
This condition exists |
1 |
The following quality relevant conditions are represented as "double bits"
in the Landsat QA band:
Condition |
Collection |
Radiometric saturation |
2 |
Cloud Confidence |
1,2 |
Cloud Shadow Confidence |
1,2 |
Snow/Ice Confidence |
1,2 |
Cirrus Confidence |
1,2 |
Possible choices for the "double bits" are:
Value |
Description |
Bit representation |
Not Determined |
Algorithm did not determine the status of this condition |
00 |
Low |
Algorithm has low to no confidence that this condition exists
(0-33 percent confidence) |
01 |
Medium |
Algorithm has medium confidence that this condition exists
(34-66 percent confidence) |
10 |
High |
Algorithm has high confidence that this condition exists
(67-100 percent confidence) |
11 |
The Landsat Quality Assessment band is an artificial band which represents
an analysis based on
defined algorithms. The USGS provides the users with the following note on
how the QA band should be used:
"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. Otherwise, users are advised that this file contains information
that can be easily misinterpreted and it is not recommended for general use."
# Create a cloud mask:
i.landsat.qa --overwrite --verbose cloud_confidence="Medium,High" \
dataset="landsat_ot_c2_l2" \
output=./Cloud_Mask_rules.txt
r.reclass input=LC81980182015183LGN00_BQA \
output=LC81980182015183LGN00_Cloud_Mask rules=./Cloud_Mask_rules.txt
# Create a water mask (only available for collection 2):
i.landsat.qa --overwrite --verbose water="Yes" \
dataset="landsat_ot_c2_l2" \
output=./Water_Mask_rules.txt
r.reclass input=LC81980182015183LGN00_BQA \
output=LC81980182015183LGN00_Water_Mask rules=./Water_Mask_rules.txt
r.reclass,
i.modis.qc,
r.bitpattern,
i.landsat
i.landsat8.swlst
Landsat Collection 1 Level 1 Quality Assessment bands
Landsat Collection 2 Level 1 Quality Assessment bands
Stefan Blumentrath, Norwegian Institute for Nature Research, Oslo (Norway)
SOURCE CODE
Available at:
i.landsat.qa source code
(history)
Latest change: Sunday Aug 18 16:05:40 2024 in commit: f9d320e265329f9ec47c8a5ff0ce4876aa53e3e0
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GRASS GIS 8.4.1dev Reference Manual