NAME

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

KEYWORDS

       imagery, landsat, acca

SYNOPSIS

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

   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

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input_prefix=string
           Base name of input raster bands
           Example: 'B.' for B.1, B.2, ...

       output=name
           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, outputing to a new raster map named 226_62.acca:
       i.landsat.toar    sensor=tm7    gain=HHHLHLHHL   date=2003-04-07   product_date=2008-11-27
       input_prefix=226_62 \
         output_prefix=226_62_toar solar_elevation=49.51654
       i.landsat.acca -f band_prefix=226_62.toar output=226_62.acca
        or
       i.landsat.toar input_prefix=L5121060_06020060714.  output_prefix=L5121060_06020060714_toar
       sensor=tm5 \
         metfile=L5121060_06020060714_MTL.txt -t
       i.landsat.acca           -5           -f           input_prefix=L5121060_06020060714_toar.
       output=L5121060_06020060714.acca
        Using the cloud mask:
        # Mask out the clouds:
        r.mapcalc "MASK = if(isnull(L5121060_06020060714.acca))"
        d.rast L5121060_06020060714_toar.1

REFERENCES

       1      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.

       2      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.landsat.toar

AUTHOR

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

       Last changed: $Date: 2011-11-08 03:23:06 -0800 (Tue, 08 Nov 2011) $

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       © 2003-2013 GRASS Development Team