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NAME

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

KEYWORDS

       imagery,  radiometric   conversion,   radiance,   reflectance,   brightness   temperature,
       atmospheric correction, satellite, Landsat

SYNOPSIS

       i.landsat.toar
       i.landsat.toar --help
       i.landsat.toar  [-rnp]  input=basename  output=basename   [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]
       [lsatmet=string[,string,...]]    [scale=float]    [--overwrite]    [--help]    [--verbose]
       [--quiet]  [--ui]

   Flags:
       -r
           Output at-sensor radiance instead of reflectance for all bands

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

       -p
           Print output metadata info

       --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=basename [required]
           Prefix for output raster maps
           Example: ’B.toar.’ generates B.toar.1, B.toar.2, ...

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

       sensor=string
           Spacecraft sensor
           Required only if ’metfile’ not given (recommended for sanity)
           Options: mss1, mss2, mss3, mss4, mss5, tm4, tm5, tm7, oli8
           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+
           oli8: Landsat_8 OLI/TIRS

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

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

       sun_elevation=float
           Sun elevation in degrees
           Required only if ’metfile’ not given

       product_date=yyyy-mm-dd
           Image creation date (yyyy-mm-dd)
           Required only if ’metfile’ not given

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

       percent=float
           Percent of solar radiance in path radiance
           Required only if ’method’ is any DOS
           Default: 0.01

       pixel=integer
           Minimum pixels to consider digital number as dark object
           Required only if ’method’ is any DOS
           Default: 1000

       rayleigh=float
           Rayleigh atmosphere (diffuse sky irradiance)
           Required only if ’method’ is DOS3
           Default: 0.0

       lsatmet=string[,string,...]
           return value stored for a given metadata
           Required only if ’metfile’ and -p given
           Options: number, creation, date, sun_elev, sensor, bands, sunaz, time
           number: Landsat Number
           creation: Creation timestamp
           date: Date
           sun_elev: Sun Elevation
           sensor: Sensor
           bands: Bands count
           sunaz: Sun Azimuth Angle
           time: Time

       scale=float
           Scale factor for output
           Default: 1.0

DESCRIPTION

       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 is 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).

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  *
               radiance_dark
       Attention:  Output radiance remain untouched (i.e. no set to 0.0 when it is negative) then
       they are possible negative values. However, output reflectance  is  set  to  0.0  when  is
       obtained a negative value.

NOTES

       The  output raster cell values can be rescaled with the scale parameter (e.g., with 100 in
       case of using reflectance output in i.gensigset).

   On Landsat-8 metadata file
       NASA reports a structure of the L1G Metadata file  (LDCM-DFCB-004.pdf)  for  Landsat  Data
       Continuity Mission (i.e. Landsat-8).

       NASA  retains  in  MIN_MAX_RADIANCE  group  the necessary information to transform Digital
       Numbers (DN) in radiance values.  Then,  i.landsat.toar  replaces  the  possible  standard
       values  with the metadata values. The results match with the values reported by the metada
       file in RADIOMETRIC_RESCALING group.

       Also, NASA reports the same values of reflectance for all bands in max-min values  and  in
       gain-bias values. This is strange that all bands have the same range of reflectance. Also,
       they wrote in the web page as to  calculate  reflectance  directly  from  DN,  first  with
       RADIOMETRIC_RESCALING values and second divided by sin(sun_elevation).

       This is a simple rescaling

           ·   reflectance  =  radiance  /  sun_radiance  = (DN * RADIANCE_MULT + RADIANCE_ADD) /
               sun_radiance

           ·   now reflectance = DN * REFLECTANCE_MULT + REFLECTANCE_ADD

           ·   then REFLECTANCE_MULT = RADIANCE_MULT / sun_radiance

           ·   and REFLECTANCE_ADD = RADIANCE_ADD / sun_radiance

       The problem arises when we need ESUN values (not provided)  to  compute  sun_radiance  and
       DOS. We assume that REFLECTANCE_MAXIMUM corresponds to the RADIANCE_MAXIMUM, then

           ·   REFLECTANCE_MAXIMUM / sin(e) = RADIANCE_MAXIMUM / sun_radiance

           ·   Esun = (PI * d^2) * RADIANCE_MAXIMUM / REFLECTANCE_MAXIMUM
       where  d  is  the  earth-sun  distance  provided  by  metadata file or computed inside the
       program.

       The i.landsat.toar reverts back the NASA rescaling to continue using Lmax, Lmin, and  Esun
       values  to compute the constant to convert DN to radiance and radiance to reflectance with
       the "traditional" equations and simple atmospheric corrections.  Attention:  When  MAXIMUM
       values  are  not  provided,  i.landsat.toar  tries  to calculate Lmax, Lmin, and Esun from
       RADIOMETRIC_RESCALING (in tests the results were the same).

   Calibration constants
       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

EXAMPLES

   Metadata file examples
       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=203_30. output=_toar \
         metfile=p203r030_7x20010620.met
       or
       i.landsat.toar input=L5121060_06020060714. \
         output=L5121060_06020060714_toar \
         metfile=L5121060_06020060714_MTL.txt
       or
       i.landsat.toar input=LC80160352013134LGN03_B output=toar \
         metfile=LC80160352013134LGN03_MTL.txt sensor=oli8 date=2013-05-14

   DOS1 example
       DN to reflectance using DOS1:
       # rename channels or make a copy to match i.landsat.toar’s input scheme:
       g.copy raster=lsat7_2002_10,lsat7_2002.1
       g.copy raster=lsat7_2002_20,lsat7_2002.2
       g.copy raster=lsat7_2002_30,lsat7_2002.3
       g.copy raster=lsat7_2002_40,lsat7_2002.4
       g.copy raster=lsat7_2002_50,lsat7_2002.5
       g.copy raster=lsat7_2002_61,lsat7_2002.61
       g.copy raster=lsat7_2002_62,lsat7_2002.62
       g.copy raster=lsat7_2002_70,lsat7_2002.7
       g.copy raster=lsat7_2002_80,lsat7_2002.8
       Calculation  of  reflectance  values  from  DN  using   DOS1   (metadata   obtained   from
       p016r035_7x20020524.met.gz):
       i.landsat.toar input=lsat7_2002. output=lsat7_2002_toar. sensor=tm7 \
         method=dos1 date=2002-05-24 sun_elevation=64.7730999 \
         product_date=2004-02-12 gain=HHHLHLHHL
       The resulting Landsat channels are named lsat7_2002_toar.1 .. lsat7_2002_toar.8.

REFERENCES

           ·   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 2011.

           ·   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.

SEE ALSO

        i.atcorr, i.colors.enhance, r.mapcalc, r.in.gdal

       Landsat Data Dictionary by USGS

AUTHOR

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

       Last changed: $Date: 2019-01-30 12:02:35 +0100 (Wed, 30 Jan 2019) $

SOURCE CODE

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

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual