Provided by: grass-doc_6.4.3-3_all
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 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] 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 --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_prefix=string 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,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 method=string Atmospheric correction method Atmospheric correction method Options: uncorrected,corrected,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
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 * radiance_dark 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 \ metfile=p203r030_7x20010620.met or i.landsat.toar input_prefix=L5121060_06020060714. \ output_prefix=L5121060_06020060714_toar \ metfile=L5121060_06020060714_MTL.txt or 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 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.
i.atcorr, r.mapcalc, r.in.gdal
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) $ Full index © 2003-2013 GRASS Development Team