i.landsat.acca - GRASS manual
Author: GRASS Development Team
Description: i.landsat.acca: Performs Landsat TM/ETM+ Automatic Cloud Cover Assessment (ACCA).
Keywords: imagery, ACCA, cloud detection, satellite, Landsat

## NAME

i.landsat.acca - Performs Landsat TM/ETM+ Automatic Cloud Cover Assessment (ACCA).

## KEYWORDS

imagery, ACCA, cloud detection, satellite, Landsat

## SYNOPSIS

i.landsat.acca
i.landsat.acca --help
i.landsat.acca [-5fx2s] input=basename output=name [b56composite=float] [b45ratio=float] [histogram=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

### Flags:

-5
  Data is Landsat-5 TM
  I.e. Thermal band is '.6' not '.61')
-f
  Apply post-processing filter to remove small holes
-x
  Always use cloud signature (step 14)
-2
  Bypass second-pass processing, and merge warm (not ambiguous) and cold clouds
-s
  Include a category for cloud shadows
--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:

input=basename [required]
  Base name of input raster bands
  Example: 'B.' for B.1, B.2, ...
output=name [required]
  Name for output raster map
b56composite=float
  B56composite (step 6)
  Default: 225.
b45ratio=float
  B45ratio: Desert detection (step 10)
  Default: 1.
histogram=integer
  Number of classes in the cloud temperature histogram
  Default: 100

## DESCRIPTION

i.landsat.acca implements the Automated Cloud-Cover Assessment (ACCA) Algorithm from Irish (2000) with the constant values for pass filter one from Irish et al. (2006). To do this, it needs Landsat band numbers 2, 3, 4, 5, and 6 (or band 61 for Landsat-7 ETM+) which have already been processed from DN into reflectance and band-6 temperature with i.landsat.toar).

The ACCA algorithm gives good results over most of the planet with the exception of ice sheets because ACCA operates on the premise that clouds are colder than the land surface they cover. The algorithm was designed for Landsat-7 ETM+ but because reflectance is used it is also useful for Landsat-4/5 TM.

## NOTES

i.landsat.acca works in the current region settings.

## EXAMPLES

Run the standard ACCA algorithm with filling of small cloud holes (the -f flag): With per-band reflectance raster maps named `226_62.toar.1, 226_62.toar.2, ...` and LANDSAT-7 thermal band `226_62.toar.61`, outputting to a new raster map named `226_62.acca`:

    i.landsat.toar sensor=7 gain=HHHLHLHHL date=2003-04-07 \
      product_date=2008-11-27 band_prefix=226_62 solar_elevation=49.51654

    i.landsat.acca -f band_prefix=226_62.toar output=226_62.acca

## REFERENCES

- Irish R.R., Barker J.L., Goward S.N., and Arvidson T., 2006. Characterization of the Landsat-7 ETM+ Automated Cloud-Cover Assessment (ACCA) Algorithm. Photogrammetric Engineering and Remote Sensing vol. 72(10): 1179-1188.
- Irish, R.R., 2000. Landsat 7 Automatic Cloud Cover Assessment. In S.S. Shen and M.R. Descour (Eds.): Algorithms for Multispectral, Hyperspectral, and Ultraspectral Imagery VI. Proceedings of SPIE, 4049: 348-355.

## SEE ALSO

i.atcorr, i.landsat.toar

## AUTHOR

E. Jorge Tizado (ej.tizado unileon es), Dept. Biodiversity and Environmental Management, University of León, Spain

## SOURCE CODE

Available at: i.landsat.acca source code (history)

Latest change: Sunday Feb 15 15:28:21 2026 in commit: 5cee43f83d1d6e0f13eb1bf2a265c2512d8ba7be

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© 2003-2026 GRASS Development Team, GRASS 8.6.0dev Reference Manual