Provided by: grass-doc_6.4.3-3_all bug


       i.landsat.toar  - Calculates top-of-atmosphere radiance or reflectance and temperature for
       Landsat MSS/TM/ETM+.


       imagery, landsat, top-of-atmosphere reflectance, dos-type simple atmospheric correction


       i.landsat.toar help
       i.landsat.toar    [-rn]    input_prefix=string    output_prefix=string      [metfile=name]
       [sensor=string]        [method=string]       [date=yyyy-mm-dd]       [sun_elevation=float]
       [product_date=yyyy-mm-dd]       [gain=string]       [percent=float]        [pixel=integer]
       [rayleigh=float]   [--verbose]  [--quiet]

           Output at-sensor radiance instead of reflectance for all bands

           Input raster maps use as extension the number of the band instead the code

           Verbose module output

           Quiet module output

           Base name of input raster bands
           Example: 'B.' for B.1, B.2, ...

           Prefix for output raster maps
           Example: 'B.toar.' generates B.toar.1, B.toar.2, ...

           Name of Landsat metadata file (.met or MTL.txt)

           Spacecraft sensor
           Required only if 'metfile' not given (recommended for sanity)
           Options: mss1,mss2,mss3,mss4,mss5,tm4,tm5,tm7,ot8
           mss1: Landsat_1 MSS
           mss2: Landsat_2 MSS
           mss3: Landsat_3 MSS
           mss4: Landsat_4 MSS
           mss5: Landsat_5 MSS
           tm4: Landsat_4 TM
           tm5: Landsat_5 TM
           tm7: Landsat_7 ETM+
           ot8: Landsat_8 OLI/TIRS

           Atmospheric correction method
           Atmospheric correction method
           Options: uncorrected,corrected,dos1,dos2,dos2b,dos3,dos4
           Default: uncorrected

           Image acquisition date (yyyy-mm-dd)
           Required only if 'metfile' not given

           Sun elevation in degrees
           Required only if 'metfile' not given

           Image creation date (yyyy-mm-dd)
           Required only if 'metfile' not given

           Gain (H/L) of all Landsat ETM+ bands (1-5,61,62,7,8)
           Required only if 'metfile' not given

           Percent of solar radiance in path radiance
           Required only if 'method' is any DOS
           Default: 0.01

           Minimum pixels to consider digital number as dark object
           Required only if 'method' is any DOS
           Default: 1000

           Rayleigh atmosphere (diffuse sky irradiance)
           Required only if 'method' is DOS3
           Default: 0.0


       i.landsat.toar  is  used  to  transform  the  calibrated digital number of Landsat imagery
       products to top-of-atmosphere radiance or top-of-atmosphere  reflectance  and  temperature
       (band  6  of  the  sensors  TM  and ETM+). Optionally, it can be used to calculate the at-
       surface radiance or reflectance with atmospheric correction (DOS method).

       Usually, to do so the production date, the acquisition date, and the solar  elevation  are
       needed.  Moreover, for Landsat-7 ETM+ it is also needed the gain (high or low) of the nine
       respective bands.

       Optionally (recommended), the data can be read from metadata file (.met  or  MTL.txt)  for
       all Landsat MSS, TM, ETM+ and OLI/TIRS. However, if the solar elevation is given the value
       of the metadata file are overwritten. This is necessary when the data in the .met file  is
       incorrect  or  not accurate. Also, if acquisition or production dates are not found in the
       metadata file then the command line values are used.

       Attention: Any null value or smaller than QCALmin in the input raster is set  to  null  in
       the output raster and it is not included in the equations.

Uncorrected at-sensor values (method=uncorrected, default)

       The  standard  geometric and radiometric corrections result in a calibrated digital number
       (QCAL = DN) images. To further standardize the impact of illumination geometry,  the  QCAL
       images  are first converted first to at-sensor radiance and then to at-sensor reflectance.
       The thermal band is first converted from QCAL to at-sensor radiance, and then to effective
       at-sensor temperature in Kelvin degrees.

       Radiometric  calibration  converts  QCAL  to  at-sensor  radiance,  a radiometric quantity
       measured in W/(m² * sr * µm) using the equations:

                      gain = (Lmax - Lmin) / (QCALmax - QCALmin)

                      bias = Lmin - gain * QCALmin

                      radiance = gain * QCAL + bias
       where, Lmax and Lmin are the calibration  constants,  and  QCALmax  and  QCALmin  are  the
       highest and the lowest points of the range of rescaled radiance in QCAL.

       Then, to calculate at-sensor reflectance the equations are:

                      sun_radiance = [Esun * sin(e)] / (PI * d^2)

                      reflectance = radiance / sun_radiance
       where,  d is the earth-sun distance in astronomical units, e is the solar elevation angle,
       and Esun is the mean solar exoatmospheric irradiance in W/(m² * µm).

Corrected at-sensor values (method=corrected)

       At-sensor reflectance values range from zero to one, whereas at-sensor  radiance  must  be
       greater  or equal to zero. However, since Lmin can be a negative number then the at-sensor
       values can also be negative. To avoid these possible negative values and set  the  minimum
       possible values at-sensor to zero, this method corrects the radiance to output a corrected
       at-sensor values using the equations (not for thermal bands):

                      radiance = (uncorrected_radiance - Lmin)

                      reflectance = radiance / sun_radiance

       Note: Other possibility to avoid negative values is set  to  zero  this  values  (radiance
       and/or reflectance), but this option is ease with uncorrected method and r.mapcalc.

Simplified at-surface values (method=dos[1-4])

       Atmospheric  correction  and  reflectance  calibration  remove the path radiance, i.e. the
       stray light from the atmosphere, and the spectral effect of solar illumination. To  output
       these  simple  at-surface  radiance and at-surface reflectance, the equations are (not for
       thermal bands):

                      sun_radiance = TAUv * [Esun * sin(e) * TAUz + Esky] / (PI * d^2)

                      radiance_path = radiance_dark - percent * sun_radiance

                      radiance = (at-sensor_radiance - radiance_path)

                      reflectance = radiance / sun_radiance
       where, percent is a value between 0.0 and 1.0 (usually 0.01),  Esky  is  the  diffuse  sky
       irradiance,  TAUz  is  the  atmospheric  transmittance  along the path from the sun to the
       ground surface, and TAUv is the atmospheric transmittance along the path from  the  ground
       surface to the sensor. radiance_dark is the at-sensor radiance calculated from the darkest
       object, i.e. DN with a least 'dark_parameter' (usually 1000) pixels for the entire  image.
       The values are,

                     DOS1: TAUv = 1.0, TAUz = 1.0 and Esky = 0.0

                     DOS2:  TAUv  = 1.0, Esky = 0.0, and TAUz = sin(e) for all bands with maximum
                     wave length less than 1. (i.e. bands 4-6 MSS, 1-4 TM, and  1-4  ETM+)  other
                     bands TAUz = 1.0

                     DOS3: TAUv = exp[-t/cos(sat_zenith)], TAUz = exp[-t/sin(e)], Esky = rayleigh

                     DOS4:  TAUv  =  exp[-t/cos(sat_zenith)],  TAUz = exp[-t/sin(e)], Esky = PI *
       Attention: Output radiance remain untouched (i.e. no set to 0. when it is  negative)  then
       they  are  possible  negative  values.  However,  output  reflectance is set to 0. when is
       obtained a negative value.


       In verbose mode  (flag  --verbose),  the  program  write  basic  satellite  data  and  the
       parameters used in the transformations.

       Production  date  is  not  an exact value but it is necessary to apply correct calibration
       constants, which were changed in the dates:

                     Landsat-1 MSS: never

                     Landsat-2 MSS: July 16, 1975

                     Landsat-3 MSS: June 1, 1978

                     Landsat-4 MSS: August 26, 1982 and April 1, 1983

                     Landsat-4 TM:  August 1, 1983 and January 15, 1984

                     Landsat-5 MSS: April 6, 1984 and November 9, 1984

                     Landsat-5 TM:  May 4, 2003 and April, 2 2007

                     Landsat-7 ETM+: July 1, 2000

                     Landsat-8 OLI/TIRS: launched in 2013


       Transform digital numbers of Landsat-7 ETM+ in band rasters 203_30.1,  203_30.2  [...]  to
       uncorrected  at-sensor  reflectance in output files 203_30.1_toar, 203_30.2_toar [...] and
       at-sensor temperature in output files 293_39.61_toar and 293_39.62_toar:
       i.landsat.toar input_prefix=203_30. output_prefix=_toar \
       i.landsat.toar input_prefix=L5121060_06020060714. \
         output_prefix=L5121060_06020060714_toar \
       i.landsat.toar input_prefix=203_30. output_prefix=_toar \
         sensor=tm7 product_date=2004-06-07 date=2001-06-20 \
         sun_elevation=64.3242970 gain="HHHLHLHHL"


                     Chander  G.,  B.L.  Markham  and  D.L.  Helder,  2009:  Remote  Sensing   of
                     Environment, vol. 113

                     Chander  G.H.  and  B.  Markham,  2003.: IEEE Transactions On Geoscience And
                     Remote Sensing, vol. 41, no. 11.

                     Chavez P.S., jr. 1996. Image-based atmospheric corrections -  Revisited  and
                     Improved. Photogrammetric Engineering and Remote Sensing 62(9): 1025-1036.

                     Huang  et al: At-Satellite Reflectance, 2002: A First Order Normalization Of
                     Landsat 7 ETM+ Images.

                     R. Irish: Landsat 7. Science Data Users Handbook. February 17, 2007; 15  May

                     Markham  B.L.  and  J.L.  Barker,  1986: Landsat MSS and TM Post-Calibration
                     Dynamic Ranges, Exoatmospheric Reflectances and  At-Satellite  Temperatures.
                     EOSAT Landsat Technical Notes, No. 1.

                     Moran M.S., R.D. Jackson, P.N. Slater and P.M. Teillet, 1992: Remote Sensing
                     of Environment, vol. 41.

                     Song et al, 2001: Classification and Change Detection Using Landsat TM Data,
                     When  and How to Correct Atmospheric Effects? Remote Sensing of Environment,
                     vol. 75.


        i.atcorr, r.mapcalc,


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

       Last changed: $Date: 2013-03-14 05:01:18 -0700 (Thu, 14 Mar 2013) $

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