Landsat Missions

Landsat Quality Assessment (QA) ArcGIS Toolbox

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Overview

Landsat Quality Assessment (QA) bands are effective for evaluating the overall usefulness of a Landsat pixel. Each pixel in the QA band contains an integer value that represents bit packed combinations of surface, atmospheric, and sensor conditions that can affect the individual pixel quality. QA bands are currently provided with Landsat Collection 1 based products, including Landsat Level-1 Standard Data Products and Higher-Level Science Data Products.

The Landsat QA ArcGIS Toolbox provides functionality to classify bit packed values for Landsat Level-1 and Higher-Level QA bands, which enhance the applications of interpreting, mapping and applying QA values to Landsat data products.  Another set of tools is the Landsat Quality Assessment (QA) Tools, which provides the functionality of extracting bit packed values to individual bands.

Below describes how to download and install the Landsat QA ArcGIS Toolbox, provides information on the Landsat QA bands, and explains how the tools operate on each Landsat band. The limitations of the tools are provided in the caveats section.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Download

The Landsat QA ArcGIS Tools can be downloaded from https://github.com/USGS-EROS/landsat-qa-arcgis-toolbox/.

Installation

The Landsat QA ArcGIS Toolbox can be installed using the following steps:

  1. Extract the contents of the .zip file.
  2. Open ArcMap or ArcCatalog.
  3. Open ArcToolbox, right-click on the top-level folder, named "ArcToolbox".
  4. Select "Add Toolbox...".
  5. Select "Landsat_QA_ArcGIS_Toolbox.pyt" from the directory extracted in Step 1.

Compatible Products

The Landsat QA ArcGIS Tools are compatible with all Landsat Collection 1 Level-1 and Higher-Level QA bands. Below is a brief description of each band’s properties.

Band Source  Product  Product Page

 BQA

 Level-1  Standard Level-1 Product  https://landsat.usgs.gov/collectionqualityband

 pixel_qa

 Higher-Level  TOA, SI, SR  https://landsat.usgs.gov/landsat-surface-reflectance-quality-assessment

 radsat_qa

 Higher-Level  TOA, SI, SR  https://landsat.usgs.gov/landsat-surface-reflectance-quality-assessment

 sr_cloud_qa  

 Higher-Level  Landsat 4-7 SR (LEDAPS)  https://landsat.usgs.gov/landsat-surface-reflectance-quality-assessment

 sr_aerosol

 Higher-Level  Landsat 8 SR (LaSRC)  https://landsat.usgs.gov/landsat-surface-reflectance-quality-assessment

BQA Level-1 Quality Assurance Band File, LaSRC Landsat Surface Reflectance Code, LEDAPS Landsat Ecosystem Disturbance Adaptive Processing System, SI Spectral Indices, SR Surface Reflectance, TOA Top of Atmosphere Reflectance

Tool: Decode QA

Currently, the only tool in the toolbox is the “Decode QA” tool, which performs the following steps:

  1. Builds an attribute table containing all unique values in the QA band,
  2. Writes a description (“Descr”) column in the attribute table,
  3. Assigns a description of each bit value in the table, and
  4. (ArcMap only) loads the band into Table of Contents in the active data frame.

An example of the graphical user interface is provided below.

Decode QA user interface image
Example of the Decode QA graphical user interface.

The result is a raster band displayed with each QA bit value assigned a label and a random color. A graphical representation is provided below.

Bit-packed pixel_qa raster before and after Decode QA tool
Graphical representation of a bit packed pixel_qa raster before (left) and after (right) the Decode QA tool is run in ArcMap.

Caveats

  • The toolbox was designed using ArcGIS version 10.4.1 and Python version 2.7.10. The functionality of the toolbox cannot be guaranteed for previous software versions, and cross-compatibility of newer and future ArcGIS and Python releases are subject to vendor discretion.
  • Input data must be in GeoTIFF (.tif), binary (.img), or other single-band raster format supported by ArcGIS. Input data must be stored in integer format; any float, double, or complex data types are not supported.
  • Any band with values outside of the supported range will not process. If you encounter this error and believe it to be an issue inherent to the tool, please submit an issue in Github or contact USGS User Services.
  • If using non-standard (i.e., user modified) file naming conventions, the tool may not correctly identify the band type, which may result in incorrect output products. Ensure the “sensor” and “band” categories are set accordingly.
  • If an attribute table already exists for the target raster, it will be overwritten by the Decode QA tool.

Contributions

If you wish to contribute feature requests, ideas, source code, or have a question regarding tool use, please submit them through the Github repository or USGS User Services.

Citation

Please use the following citation when referencing this software:
U.S. Geological Survey, 2017. Landsat Quality Assurance ArcGIS Toolbox. U.S. Geological Survey software release. doi:10.5066/F7JM284N.

About

Landsat represents the world's longest continuously acquired collection of space-based moderate-resolution land remote sensing data. Four decades of imagery provides a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global change research. Landsat images are also invaluable for emergency response and disaster relief.

 

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