Provided by: grass-doc_7.6.1-3_all bug

NAME

       i.atcorr  - Performs atmospheric correction using the 6S algorithm.
       6S - Second Simulation of Satellite Signal in the Solar Spectrum.

KEYWORDS

       imagery, atmospheric correction, radiometric conversion, radiance, reflectance, satellite

SYNOPSIS

       i.atcorr
       i.atcorr --help
       i.atcorr   [-irab]   input=name   [range=min,max]    [elevation=name]    [visibility=name]
       parameters=name  output=name   [rescale=min,max]    [--overwrite]   [--help]   [--verbose]
       [--quiet]  [--ui]

   Flags:
       -i
           Output raster map as integer

       -r
           Input raster map converted to reflectance (default is radiance)

       -a
           Input from ETM+ image taken after July 1, 2000

       -b
           Input from ETM+ image taken before July 1, 2000

       --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=name [required]
           Name of input raster map

       range=min,max
           Input range
           Default: 0,255

       elevation=name
           Name of input elevation raster map (in m)

       visibility=name
           Name of input visibility raster map (in km)

       parameters=name [required]
           Name of input text file with 6S parameters

       output=name [required]
           Name for output raster map

       rescale=min,max
           Rescale output raster map
           Default: 0,255

DESCRIPTION

       i.atcorr  performs  atmospheric  correction on the input raster map using the 6S algorithm
       (Second Simulation of Satellite Signal  in  the  Solar  Spectrum).  A  detailed  algorithm
       description  is  available  at  the  Land  Surface  Reflectance Science Computing Facility
       website.

       Important: Current region settings are ignored! The region is adjusted to cover the  input
       raster  map  before  the  atmospheric  correction  is performed. The previous settings are
       restored afterwards.

       If the -r flag is used, the input raster map is treated  as  reflectance.  Otherwise,  the
       input  raster  map is treated as radiance values and it is converted to reflectance at the
       i.atcorr runtime. The output data are always reflectance.

       The satellite overpass time has to be specified in Greenwich Mean Time (GMT).

       An example of the 6S parameters could be:
       8                            - geometrical conditions=Landsat ETM+
       2 19 13.00 -47.410 -20.234   - month day hh.ddd longitude latitude ("hh.ddd" is in decimal hours GMT)
       1                            - atmospheric model=tropical
       1                            - aerosols model=continental
       15                           - visibility [km] (aerosol model concentration)
       -0.600                       - mean target elevation above sea level [km] (here 600 m asl)
       -1000                        - sensor height (here, sensor on board a satellite)
       64                           - 4th band of ETM+ Landsat 7
       If the position is not available in  longitude-latitude  (WGS84),  the  m.proj  conversion
       module can be used to reproject from a different reference system.

6S CODE PARAMETER CHOICES

   A. Geometrical conditions
       Code                                                         Description                                                  Details

       1                                                            meteosat observation                                         enter  month,day,decimal  hour (universal time-hh.ddd) n. of
                                                                                                                                 column,n. of line. (full scale 5000*2500)

       2                                                            goes east observation                                        enter month,day,decimal hour (universal time-hh.ddd)  n.  of
                                                                                                                                 column,n. of line. (full scale 17000*12000)c

       3                                                            goes west observation                                        enter  month,day,decimal  hour (universal time-hh.ddd) n. of
                                                                                                                                 column,n. of line. (full scale 17000*12000)

       4                                                            avhrr (PM noaa)                                              enter month,day,decimal hour (universal time-hh.ddd)  n.  of
                                                                                                                                 column(1-2048),xlonan,hna  give  long.(xlonan)  and overpass
                                                                                                                                 hour (hna) at the ascendant node at equator

       5                                                            avhrr (AM noaa)                                              enter month,day,decimal hour (universal time-hh.ddd)  n.  of
                                                                                                                                 column(1-2048),xlonan,hna  give  long.(xlonan)  and overpass
                                                                                                                                 hour (hna) at the ascendant node at equator

       6                                                            hrv (spot)                                                   enter month,day,hh.ddd,long.,lat. *

       7                                                            tm (landsat)                                                 enter month,day,hh.ddd,long.,lat. *

       8                                                            etm+ (landsat7)                                              enter month,day,hh.ddd,long.,lat. *

       9                                                            liss (IRS 1C)                                                enter month,day,hh.ddd,long.,lat. *

       10                                                           aster                                                        enter month,day,hh.ddd,long.,lat. *

       11                                                           avnir                                                        enter month,day,hh.ddd,long.,lat. *

       12                                                           ikonos                                                       enter month,day,hh.ddd,long.,lat. *

       13                                                           RapidEye                                                     enter month,day,hh.ddd,long.,lat. *

       14                                                           VGT1 (SPOT4)                                                 enter month,day,hh.ddd,long.,lat. *

       15                                                           VGT2 (SPOT5)                                                 enter month,day,hh.ddd,long.,lat. *

       16                                                           WorldView 2                                                  enter month,day,hh.ddd,long.,lat. *

       17                                                           QuickBird                                                    enter month,day,hh.ddd,long.,lat. *

       18                                                           LandSat 8                                                    enter month,day,hh.ddd,long.,lat. *

       19                                                           Geoeye 1                                                     enter month,day,hh.ddd,long.,lat. *

       20                                                           Spot6                                                        enter month,day,hh.ddd,long.,lat. *

       21                                                           Spot7                                                        enter month,day,hh.ddd,long.,lat. *

       22                                                           Pleiades1A                                                   enter month,day,hh.ddd,long.,lat. *

       23                                                           Pleiades1B                                                   enter month,day,hh.ddd,long.,lat. *

       24                                                           Worldview3                                                   enter month,day,hh.ddd,long.,lat. *

       25                                                           Sentinel-2A                                                  enter month,day,hh.ddd,long.,lat. *

       26                                                           Sentinel-2B                                                  enter month,day,hh.ddd,long.,lat. *

       27                                                           PlanetScope 0c 0d                                            enter month,day,hh.ddd,long.,lat. *

       28                                                           PlanetScope 0e                                               enter month,day,hh.ddd,long.,lat. *

       29                                                           PlanetScope 0f 10                                            enter month,day,hh.ddd,long.,lat. *

       NOTE: for HRV, TM, ETM+, LISS and  ASTER  experiments,  longitude  and  latitude  are  the
       coordinates  of the scene center. Latitude must be > 0 for northern hemisphere and < 0 for
       southern. Longitude must be > 0 for eastern hemisphere and < 0 for western.

   B. Atmospheric model
       Code                                                         Meaning

       0                                                            no gaseous absorption

       1                                                            tropical

       2                                                            midlatitude summer

       3                                                            midlatitude winter

       4                                                            subarctic summer

       5                                                            subarctic winter

       6                                                            us standard 62

       7                                                            Define your own atmospheric model as a set of the  following
                                                                    5  parameters  per  each measurement: altitude [km] pressure
                                                                    [mb] temperature [k] h2o density [g/m3]  o3  density  [g/m3]
                                                                    For  example:  there  is one radiosonde measurement for each
                                                                    altitude of 0-25km at a step of 1km, one measurment for each
                                                                    altitude  of  25-50km  at  a  step  of  5km,  and two single
                                                                    measurements for altitudes 70km and  100km.  This  makes  34
                                                                    measurments. In that case, there are 34*5 values to input.

       8                                                            Define  your  own  atmospheric model providing values of the
                                                                    water vapor and ozone content: uw [g/cm2] uo3  [cm-atm]  The
                                                                    profile is taken from us62.

   C. Aerosols model
       Code                                                         Meaning                                                      Details

       0                                                            no aerosols

       1                                                            continental model

       2                                                            maritime model

       3                                                            urban model

       4                                                            shettle model for background desert aerosol

       5                                                            biomass burning

       6                                                            stratospheric model

       7                                                            define your own model                                        Enter  the  volumic  percentage  of  each  component: c(1) =
                                                                                                                                 volumic % of dust-like c(2) =  volumic  %  of  water-soluble
                                                                                                                                 c(3)  =  volumic  %  of oceanic c(4) = volumic % of soot All
                                                                                                                                 values should be between 0 and 1.

       8                                                            define your own model                                        Size distribution function: Multimodal Log Normal (up  to  4
                                                                                                                                 modes).

       9                                                            define your own model                                        Size distribution function: Modified gamma.

       10                                                           define your own model                                        Size distribution function: Junge Power-Law.

       11                                                           define your own model                                        Sun-photometer  measurements,  50  values max, entered as: r
                                                                                                                                 and d V / d (logr) where r is the radius [micron], V is  the
                                                                                                                                 volume,  d  V  / d (logr) [cm3/cm2/micron].  Followed by: nr
                                                                                                                                 and ni for each wavelength where nr and ni are  respectively
                                                                                                                                 the real and imaginary part of the refractive index.

   D. Aerosol concentration model (visibility)
       If  you  have an estimate of the meteorological parameter visibility v, enter directly the
       value of v [km] (the aerosol optical depth (AOD) will be computed from a standard  aerosol
       profile).

       If  you  have  an  estimate  of aerosol optical depth, enter 0 for the visibility and in a
       following line enter the aerosol optical depth at 550nm (iaer  means  ’i’  for  input  and
       ’aer’ for aerosol), for example:
       0                            - visibility
       0.112                        - aerosol optical depth at 550 nm

       NOTE: if iaer is 0, enter -1 for visibility.

       NOTE: if a visibility map is provided, these parameters are ignored.

   E. Target altitude (xps), sensor platform (xpp)
       Target altitude (xps, in negative [km]): xps >= 0 means the target is at the sea level.
       otherwise  xps  expresses the altitude of the target (e.g., mean elevation) in [km], given
       as negative value
       Sensor platform (xpp, in negative [km] or -1000):
       xpp = -1000 means that the sensor is on board a satellite.
       xpp = 0 means that the sensor is at the ground level.
       -100 < xpp < 0 defines the altitude of the sensor expressed  in  [km];  this  altitude  is
       given relative to the target altitude as negative value.

       For  aircraft  simulations  only  (xpp  is neither equal to 0 nor equal to -1000): puw,po3
       (water vapor content,ozone content between the aircraft and the surface)
       taerp (the aerosol optical thickness at 550nm between the aircraft and the surface)

       If these data are not available, enter negative values for all of them.  puw,po3 will then
       be  interpolated  from  the  us62  standard  profile according to the values at the ground
       level; taerp will be computed according to a 2 km exponential profile for aerosol.

   F. Sensor band
       There are two possibilities: either define your own spectral conditions (codes -2, -1,  0,
       or 1) or choose a code indicating the band of one of the pre-defined satellites.

       Define your own spectral conditions:

       Code                                                         Meaning

       -2                                                           Enter  wlinf, wlsup.  The filter function will be equal to 1
                                                                    over the whole band (as iwave=0) but  step  by  step  output
                                                                    will be printed.

       -1                                                           Enter wl (monochr. cond, gaseous absorption is included).

       0                                                            Enter  wlinf, wlsup.  The filter function will be equal to 1
                                                                    over the whole band.

       1                                                            Enter wlinf, wlsup and user’s filter function s (lambda)  by
                                                                    step of 0.0025 micrometer.

       Pre-defined satellite bands:

       Code                                                         Band name (peak response)

       2                                                            meteosat vis band (0.350-1.110)

       3                                                            goes east band vis (0.490-0.900)

       4                                                            goes west band vis (0.490-0.900)

       5                                                            avhrr (noaa6) band 1 (0.550-0.750)

       6                                                            avhrr (noaa6) band 2 (0.690-1.120)

       7                                                            avhrr (noaa7) band 1 (0.500-0.800)

       8                                                            avhrr (noaa7) band 2 (0.640-1.170)

       9                                                            avhrr (noaa8) band 1 (0.540-1.010)

       10                                                           avhrr (noaa8) band 2 (0.680-1.120)

       11                                                           avhrr (noaa9) band 1 (0.530-0.810)

       12                                                           avhrr (noaa9) band 1 (0.680-1.170)

       13                                                           avhrr (noaa10) band 1 (0.530-0.780)

       14                                                           avhrr (noaa10) band 2 (0.600-1.190)

       15                                                           avhrr (noaa11) band 1 (0.540-0.820)

       16                                                           avhrr (noaa11) band 2 (0.600-1.120)

       17                                                           hrv1 (spot1) band 1 (0.470-0.650)

       18                                                           hrv1 (spot1) band 2 (0.600-0.720)

       19                                                           hrv1 (spot1) band 3 (0.730-0.930)

       20                                                           hrv1 (spot1) band pan (0.470-0.790)

       21                                                           hrv2 (spot1) band 1 (0.470-0.650)

       22                                                           hrv2 (spot1) band 2 (0.590-0.730)

       23                                                           hrv2 (spot1) band 3 (0.740-0.940)

       24                                                           hrv2 (spot1) band pan (0.470-0.790)

       25                                                           tm (landsat5) band 1 (0.430-0.560)

       26                                                           tm (landsat5) band 2 (0.500-0.650)

       27                                                           tm (landsat5) band 3 (0.580-0.740)

       28                                                           tm (landsat5) band 4 (0.730-0.950)

       29                                                           tm (landsat5) band 5 (1.5025-1.890)

       30                                                           tm (landsat5) band 7 (1.950-2.410)

       31                                                           mss (landsat5) band 1 (0.475-0.640)

       32                                                           mss (landsat5) band 2 (0.580-0.750)

       33                                                           mss (landsat5) band 3 (0.655-0.855)

       34                                                           mss (landsat5) band 4 (0.785-1.100)

       35                                                           MAS (ER2) band 1 (0.5025-0.5875)

       36                                                           MAS (ER2) band 2 (0.6075-0.7000)

       37                                                           MAS (ER2) band 3 (0.8300-0.9125)

       38                                                           MAS (ER2) band 4 (0.9000-0.9975)

       39                                                           MAS (ER2) band 5 (1.8200-1.9575)

       40                                                           MAS (ER2) band 6 (2.0950-2.1925)

       41                                                           MAS (ER2) band 7 (3.5800-3.8700)

       42                                                           MODIS band 1 (0.6100-0.6850)

       43                                                           MODIS band 2 (0.8200-0.9025)

       44                                                           MODIS band 3 (0.4500-0.4825)

       45                                                           MODIS band 4 (0.5400-0.5700)

       46                                                           MODIS band 5 (1.2150-1.2700)

       47                                                           MODIS band 6 (1.6000-1.6650)

       48                                                           MODIS band 7 (2.0575-2.1825)

       49                                                           avhrr (noaa12) band 1 (0.500-1.000)

       50                                                           avhrr (noaa12) band 2 (0.650-1.120)

       51                                                           avhrr (noaa14) band 1 (0.500-1.110)

       52                                                           avhrr (noaa14) band 2 (0.680-1.100)

       53                                                           POLDER band 1 (0.4125-0.4775)

       54                                                           POLDER band 2 (non polar) (0.4100-0.5225)

       55                                                           POLDER band 3 (non polar) (0.5325-0.5950)

       56                                                           POLDER band 4 P1 (0.6300-0.7025)

       57                                                           POLDER band 5 (non polar) (0.7450-0.7800)

       58                                                           POLDER band 6 (non polar) (0.7000-0.8300)

       59                                                           POLDER band 7 P1 (0.8100-0.9200)

       60                                                           POLDER band 8 (non polar) (0.8650-0.9400)

       61                                                           etm+ (landsat7) band 1 blue (435nm - 517nm)

       62                                                           etm+ (landsat7) band 2 green (508nm - 617nm)

       63                                                           etm+ (landsat7) band 3 red (625nm - 702nm)

       64                                                           etm+ (landsat7) band 4 NIR (753nm - 910nm)

       65                                                           etm+ (landsat7) band 5 SWIR (1520nm - 1785nm)

       66                                                           etm+ (landsat7) band 7 SWIR (2028nm - 2375nm)

       67                                                           etm+ (landsat7) band 8 PAN (505nm - 917nm)

       68                                                           liss (IRC 1C) band 2 (0.502-0.620)

       69                                                           liss (IRC 1C) band 3 (0.612-0.700)

       70                                                           liss (IRC 1C) band 4 (0.752-0.880)

       71                                                           liss (IRC 1C) band 5 (1.452-1.760)

       72                                                           aster band 1 (0.480-0.645)

       73                                                           aster band 2 (0.588-0.733)

       74                                                           aster band 3N (0.723-0.913)

       75                                                           aster band 4 (1.530-1.750)

       76                                                           aster band 5 (2.103-2.285)

       77                                                           aster band 6 (2.105-2.298)

       78                                                           aster band 7 (2.200-2.393)

       79                                                           aster band 8 (2.248-2.475)

       80                                                           aster band 9 (2.295-2.538)

       81                                                           avnir band 1 (408nm - 517nm)

       82                                                           avnir band 2 (503nm - 612nm)

       83                                                           avnir band 3 (583nm - 717nm)

       84                                                           avnir band 4 (735nm - 922nm)

       85                                                           Ikonos Green band (408nm - 642nm)

       86                                                           Ikonos Red band (448nm - 715nm)

       87                                                           Ikonos NIR band (575nm - 787nm)

       88                                                           RapidEye Blue band (440nm - 512nm)

       89                                                           RapidEye Green band (515nm - 592nm)

       90                                                           RapidEye Red band (628nm - 687nm)

       91                                                           RapidEye Red edge band (685nm - 735nm)

       92                                                           RapidEye NIR band (750nm - 860nm)

       93                                                           VGT1 (SPOT4) band 0 (420nm - 497nm)

       94                                                           VGT1 (SPOT4) band 2 (603nm - 747nm)

       95                                                           VGT1 (SPOT4) band 3 (740nm - 942nm)

       96                                                           VGT1 (SPOT4) MIR band (1540nm - 1777nm)

       97                                                           VGT2 (SPOT5) band 0 (423nm - 492nm)

       98                                                           VGT2 (SPOT5) band 2 (600nm - 737nm)

       99                                                           VGT2 (SPOT5) band 3 (745nm - 945nm)

       100                                                          VGT2 (SPOT5) MIR band (1523nm - 1757nm)

       101                                                          WorldView2 Panchromatic band (448nm - 812nm)

       102                                                          WorldView2 Coastal Blue band (395nm - 457nm)

       103                                                          WorldView2 Blue band (440nm - 517nm)

       104                                                          WorldView2 Green band (503nm - 587nm)

       105                                                          WorldView2 Yellow band (583nm - 632nm)

       106                                                          WorldView2 Red band (623nm - 695nm)

       107                                                          WorldView2 Red edge band (698nm - 750nm)

       108                                                          WorldView2 NIR1 band (760nm - 905nm)

       109                                                          WorldView2 NIR2 band (853nm - 1047nm)

       110                                                          QuickBird Panchromatic band (385nm - 1060nm)

       111                                                          QuickBird Blue band (420nm - 585nm)

       112                                                          QuickBird Green band (448nm - 682nm)

       113                                                          QuickBird Red band (560nm - 747nm)

       114                                                          QuickBird NIR1 band (650nm - 935nm)

       115                                                          Landsat 8 Coastal aerosol band (433nm - 455nm)

       116                                                          Landsat 8 Blue band (448nm - 515nm)

       117                                                          Landsat 8 Green band (525nm - 595nm)

       118                                                          Landsat 8 Red band (633nm - 677nm)

       119                                                          Landsat 8 Panchromatic band (498nm - 682nm)

       120                                                          Landsat 8 NIR band (845nm - 885nm)

       121                                                          Landsat 8 Cirrus band (1355nm - 1390nm)

       122                                                          Landsat 8 SWIR1 band (1540nm - 1672nm)

       123                                                          Landsat 8 SWIR2 band (2073nm - 2322nm)

       124                                                          GeoEye 1 Panchromatic band (448nm - 812nm)

       125                                                          GeoEye 1 Blue band (443nm - 525nm)

       126                                                          GeoEye 1 Green band (503nm - 587nm)

       127                                                          GeoEye 1 Red band (653nm - 697nm)

       128                                                          GeoEye 1 NIR band (770nm - 932nm)

       129                                                          Spot6 Blue band (440nm - 532nm)

       130                                                          Spot6 Green band (515nm - 600nm)

       131                                                          Spot6 Red band (610nm - 710nm)

       132                                                          Spot6 NIR band (738nm - 897nm)

       133                                                          Spot6 Pan band (438nm - 760nm)

       134                                                          Spot7 Blue band (445nm - 532nm)

       135                                                          Spot7 Green band (525nm - 607nm)

       136                                                          Spot7 Red band (610nm - 727nm)

       137                                                          Spot7 NIR band (745nm - 902nm)

       138                                                          Spot7 Pan band (443nm - 760nm)

       139                                                          Pleiades1A Blue band (433nm - 560nm)

       140                                                          Pleiades1A Green band (500nm - 617nm)

       141                                                          Pleiades1A Red band (590nm - 722nm)

       142                                                          Pleiades1A NIR band (740nm - 945nm)

       143                                                          Pleiades1A Pan band (460nm - 845nm)

       144                                                          Pleiades1B Blue band 438nm - 560nm)

       145                                                          Pleiades1B Green band (498nm - 615nm)

       146                                                          Pleiades1B Red band (608nm - 727nm)

       147                                                          Pleiades1B NIR band (750nm - 945nm)

       148                                                          Pleiades1B Pan band (460nm - 845nm)

       149                                                          Worldview3 Pan band (445nm - 812nm)

       150                                                          Worldview3 Coastal blue band (395nm - 455nm)

       151                                                          Worldview3 Blue band (443nm - 517nm)

       152                                                          Worldview3 Green band (508nm - 587nm)

       153                                                          Worldview3 Yellow band (580nm - 630nm)

       154                                                          Worldview3 Red band 625nm - 697nm)

       155                                                          Worldview3 Red edge band (698nm - 752nm)

       156                                                          Worldview3 NIR1 band (760nm - 902nm)

       157                                                          Worldview3 NIR2 band (855nm - 1042nm)

       158                                                          Worldview3 SWIR1 band (1178nm - 1242nm)

       159                                                          Worldview3 SWIR2 band (1545nm - 1600nm)

       160                                                          Worldview3 SWIR3 band (1633nm - 1687nm)

       161                                                          Worldview3 SWIR4 band (1698nm - 1762nm)

       162                                                          Worldview3 SWIR5 band (2133nm - 2195nm)

       163                                                          Worldview3 SWIR6 band (2170nm - 2235nm)

       164                                                          Worldview3 SWIR7 band (2225nm - 2295nm)

       165                                                          Worldview3 SWIR8 band (2283nm - 2377nm)

       166                                                          Sentinel2A Coastal blue band B1 (430nm - 455nm)

       167                                                          Sentinel2A Blue band B2 (440nm - 530nm)

       168                                                          Sentinel2A Green band B3 (540nm - 580nm)

       169                                                          Sentinel2A Red band B4 (648nm - 682nm)

       170                                                          Sentinel2A Red edge band B5 (695nm - 712nm)

       171                                                          Sentinel2A Red edge band B6 (733nm - 747nm)

       172                                                          Sentinel2A Red edge band B7 (770nm - 795nm)

       173                                                          Sentinel2A NIR band B8 (775nm - 905nm)

       174                                                          Sentinel2A Red edge band B8A (850nm - 880nm)

       175                                                          Sentinel2A Water vapour band B9 (933nm - 957nm)

       176                                                          Sentinel2A SWIR Cirrus band B10 (1355nm - 1392nm)

       177                                                          Sentinel2A SWIR band B11 (1558nm - 1667nm)

       178                                                          Sentinel2A SWIR band B12 (2088nm - 2315nm)

       179                                                          Sentinel2B Coastal blue band B1 (430nm - 455nm)

       180                                                          Sentinel2B Blue band B2 (440nm - 530nm)

       181                                                          Sentinel2B Green band B3 (538nm - 580nm)

       182                                                          Sentinel2B Red band B4 (648nm - 682nm)

       183                                                          Sentinel2B Red edge band B5 (695nm - 712nm)

       184                                                          Sentinel2B Red edge band B6 (730nm - 747nm)

       185                                                          Sentinel2B Red edge band B7 (768nm - 792nm)

       186                                                          Sentinel2B NIR band B8 (778nm - 905nm)

       187                                                          Sentinel2B Red edge band B8A (850nm - 877nm)

       188                                                          Sentinel2B Water vapour band B9 (930nm - 955nm)

       189                                                          Sentinel2B SWIR Cirrus band B10 (1358nm - 1397nm)

       190                                                          Sentinel2B SWIR band B11 (1555nm - 1667nm)

       191                                                          Sentinel2B SWIR band B12 (2075nm - 2300nm)

       192                                                          PlanetScope 0c 0d Blue band B1 (440nm - 570nm)

       193                                                          PlanetScope 0c 0d Green band B2 (450nm - 690nm)

       194                                                          PlanetScope 0c 0d Red band B3 (460nm - 700nm)

       195                                                          PlanetScope 0c 0d NIR band B4 (770nm - 880nm)

       196                                                          PlanetScope 0e Blue band B1 (430nm - 700nm)

       197                                                          PlanetScope 0e Green band B2 (450nm - 700nm)

       198                                                          PlanetScope 0e Red band B3 (460nm - 700nm)

       199                                                          PlanetScope 0e NIR band B4 (760nm - 880nm)

       200                                                          PlanetScope 0f 10 Blue band B1 (450nm - 680nm)

       201                                                          PlanetScope 0f 10 Green band B2 (450nm - 680nm)

       202                                                          PlanetScope 0f 10 Red band B3 (450nm - 680nm)

       203                                                          PlanetScope 0f 10 NIR band B4 (760nm - 870nm)

EXAMPLES

   Atmospheric correction of a Sentinel-2 band
       This  example  illustrates  how to perform atmospheric correction of a Sentinel-2 scene in
       the North Carolina location.

       Let’s         assume         that         the         Sentinel-2         L1C         scene
       S2A_OPER_PRD_MSIL1C_PDMC_20161029T092602_R054_V20161028T155402_20161028T155402         was
       downloaded and imported with region cropping (see r.import) into the PERMANENT  mapset  of
       the  North  Carolina  location.  The  computational  region  was  set to the extent of the
       elevation map in the North Carolina dataset. Now, we have 13  individual  bands  (B01-B12)
       that  we  want to apply the atmospheric correction to.  The following steps are applied to
       each band separately.

       Create the parameters file for i.atcorr

       In the first step we create a file containing the 6S parameters for a particular scene and
       band. To create a 6S file, we need to obtain the following information:

           ·   geometrical conditions,

           ·   moth, day, decimal hours in GMT, decimal longitude and latitude of measurement,

           ·   atmospheric model,

           ·   aerosol model,

           ·   visibility or aerosol optical depth,

           ·   mean target elevation above sea level,

           ·   sensor height and,

           ·   sensor band.

       1      Geometrical conditions

       For  Sentinel-2A,  the  geometrical  conditions take the value 25 and for Sentinel-2B, the
       geometrical conditions value is 26 (See table A).  Our scene comes  from  the  Sentinel-2A
       mission (the file name begins with S2A_...).

       2      Day, time, longitude and latitude of measurement

       Day  and time of the measurement are hidden in the filename (i.e., the second datum in the
       file name with format YYYYMMDDTHHMMSS), and are also noted in the metadata file, which  is
       included in the downloaded scene (file with .xml extension). Our sample scene was taken on
       October 28th (20161028) at 15:54:02 (155402). Note that the time has to  be  specified  in
       decimal  hours in Greenwich Mean Time (GMT). Luckily, the time in the scene name is in GMT
       and we can convert it to decimal hours as follows: 15 + 54/60 + 2/3600 = 15.901.

       Longitude and latitude refer to the centre of  the  computational  region  (which  can  be
       smaller  than  the  scene),  and  must  be  in  WGS84  decimal  coordinates. To obtain the
       coordinates of the centre, we can run:
       g.region -bg

       The longitude and latitude of the centre are stored in ll_clon and ll_clat. In  our  case,
       ll_clon=-78.691 and ll_clat=35.749.

       3      Atmospheric model

       We  can  choose  between  various  atmospheric  models as defined at the beginning of this
       manual. For North Carolina, we can choose 2 - midlatitude summer.

       4      Aerosol model

       We can also choose between various aerosol models as defined  at  the  beginning  of  this
       manual. For North Carolina, we can choose 1 - continental model.

       5      Visibility or Aerosol Optical Depth

       For  Sentinel-2  scenes, the visibility is not measured, and therefore we have to estimate
       the aerosol optical depth instead, e.g. from AERONET. With a bit of luck, you can  find  a
       station  nearby  your  location, which measured the Aerosol Optical Depth at 500 nm at the
       same  time  as  the  scene  was  taken.  In  our  case,  on   28th   October   2016,   the
       EPA-Res_Triangle_Pk station measured AOD = 0.07 (approximately).

       6      Mean target elevation above sea level

       Mean  target  elevation  above sea level refers to the mean elevation of the computational
       region. You can estimate it from the digital elevation model, e.g. by running:
       r.univar -g elevation

       The mean elevation is stored in mean. In our case, mean=110. In the 6S  file  it  will  be
       displayed in [-km], i.e., -0.110.

       7      Sensor height

       Since the sensor is on board a satellite, the sensor height will be set to -1000.

       8      Sensor band

       The overview of satellite bands can be found in table F (see above).  For Sentinel-2A, the
       band numbers span from 166 to 178, and for Sentinel-2B, from 179 to 191.

       Finally, here is what the 6S file would look like for Band 02 of our scene.  In  order  to
       use it in the i.atcorr module, we can save it in a text file, for example params_B02.txt.
       25
       10 28 15.901 -78.691 35.749
       2
       1
       0
       0.07
       -0.110
       -1000
       167

       Compute atmospheric correction

       In  the  next  step  we run i.atcorr for the selected band B02 of our Sentinel 2 scene. We
       have to specify the following parameters:

           ·   input = raster band to be processed,

           ·   parameters = path to 6S file created in the previous step (we could also enter the
               values directly),

           ·   output = name for the output corrected raster band,

           ·   range  =  from  1  to  the QUANTIFICATION_VALUE stored in the metadata file. It is
               10000 for both Sentinel-2A and Sentinel-2B.

           ·   rescale = the output range of values for the corrected bands. This is  up  to  the
               user to choose, for example: 0-255, 0-1, 1-10000.

       If the data is available, the following parameters can be specified as well:

           ·   elevation = raster of digital elevation model,

           ·   visibility = raster of visibility model.

       Finally,  this  is how the command would look like to apply atmospheric correction to band
       B02:
       i.atcorr input=B02 parameters=params_B02.txt output=B02.atcorr range=1,10000 rescale=0,255 elevation=elevation

       To apply atmospheric correction to the remaining bands, only  the  last  line  in  the  6S
       parameters  file  (i.e.,  the sensor band) needs to be changed.  The other parameters will
       remain the same.
       Figure: Sentinel-2A Band 02 with applied atmospheric  correction  (histogram  equalization
       grayscale color scheme)

   Atmospheric correction of a Landsat-7 band
       This  example is also based on the North Carolina sample dataset (GMT -5 hours).  First we
       set the computational region to the satellite map, e.g. band 4:
       g.region raster=lsat7_2002_40 -p

       It is important to verify the available metadata for the sun  position  which  has  to  be
       defined  for the atmospheric correction. An option is to check the satellite overpass time
       with sun position as reported in the metadata  file  (file  copy;  North  Carolina  sample
       dataset).  In the case of the North Carolina sample dataset, these values have been stored
       for each channel and can be retrieved with:
       r.info lsat7_2002_40
       In this case, we have: SUN_AZIMUTH = 120.8810347, SUN_ELEVATION = 64.7730999.

       If the sun position metadata are unavailable, we can also calculate them from the overpass
       time as follows (r.sunmask uses SOLPOS):
       r.sunmask -s elev=elevation out=dummy year=2002 month=5 day=24 hour=10 min=42 sec=7 timezone=-5
       # .. reports: sun azimuth: 121.342461, sun angle above horz.(refraction corrected): 65.396652
       If the overpass time is unknown, use the NASA LaRC Satellite Overpass Predictor.

   Convert digital numbers (DN) to radiance at top-of-atmosphere (TOA)
       For  Landsat  and  ASTER,  the  conversion can be conveniently done with i.landsat.toar or
       i.aster.toar, respectively.

       In case of different satellites, the conversion of DN (digital number = pixel  values)  to
       radiance at top-of-atmosphere (TOA) can also be done manually, using e.g. the formula:
       # formula depends on satellite sensor, see respective metadata
       L&#955; = ((LMAX&#955; - LMIN&#955;)/(QCALMAX-QCALMIN)) * (QCAL-QCALMIN) + LMIN&#955;
       where,

           ·   L&#955; = Spectral Radiance at the sensor’s aperture in Watt/(meter squared * ster
               * µm), the apparent radiance as seen by the satellite sensor;

           ·   QCAL = the quantized calibrated pixel value in DN;

           ·   LMIN&#955; = the spectral radiance that  is  scaled  to  QCALMIN  in  watts/(meter
               squared * ster * µm);

           ·   LMAX&#955;  =  the  spectral  radiance  that  is scaled to QCALMAX in watts/(meter
               squared * ster * µm);

           ·   QCALMIN  =  the  minimum  quantized  calibrated  pixel  value  (corresponding   to
               LMIN&#955;) in DN;

           ·   QCALMAX   =  the  maximum  quantized  calibrated  pixel  value  (corresponding  to
               LMAX&#955;) in DN=255.
       LMIN&#955; and LMAX&#955; are the radiances related to the minimal and maximal  DN  value,
       and  they  are  reported in the metadata file of each image. High gain or low gain is also
       reported in the metadata file of each satellite image. For Landsat ETM+,  the  minimal  DN
       value  (QCALMIN)  is  1  (see  Landsat  handbook,  chapter  11),  and the maximal DN value
       (QCALMAX) is 255. QCAL is the DN value for every separate pixel in the Landsat image.

       We extract the coefficients and apply them in order to obtain the radiance map:
       CHAN=4
       r.info lsat7_2002_${CHAN}0 -h | tr ’\n’ ’ ’ | sed ’s+ ++g’ | tr ’:’ ’\n’ | grep "LMIN_BAND${CHAN}\|LMAX_BAND${CHAN}"
       LMAX_BAND4=241.100,p016r035_7x20020524.met
       LMIN_BAND4=-5.100,p016r035_7x20020524.met
       QCALMAX_BAND4=255.0,p016r035_7x20020524.met
       QCALMIN_BAND4=1.0,p016r035_7x20020524.met
       Conversion to radiance (this calculation is done for band 4,  for  the  other  bands,  the
       numbers will need to be replaced with their related values):
       r.mapcalc "lsat7_2002_40_rad = ((241.1 - (-5.1)) / (255.0 - 1.0)) * (lsat7_2002_40 - 1.0) + (-5.1)"
       Again,  the  r.mapcalc  calculation  is only needed when working with satellite data other
       than Landsat or ASTER.

   Create the parameters file for i.atcorr
       The underlying 6S model is  parametrized  through  a  control  file,  indicated  with  the
       parameters  option.  This is a text file defining geometrical and atmospherical conditions
       of the satellite overpass.  Here we create a control file icnd_lsat4.txt for band 4 (NIR),
       based  on  metadata.  For  the overpass time, we need to define decimal hours: 10:42:07 NC
       local time = 10.70 decimal hours (decimal minutes: 42 * 100 / 60) which is 15.70 GMT.
       8                            - geometrical conditions=Landsat ETM+
       5 24 15.70 -78.691 35.749    - month day hh.ddd longitude latitude ("hh.ddd" is in GMT decimal hours)
       2                            - atmospheric model=midlatitude summer
       1                            - aerosols model=continental
       50                           - visibility [km] (aerosol model concentration)
       -0.110                       - mean target elevation above sea level [km]
       -1000                        - sensor on board a satellite
       64                           - 4th band of ETM+ Landsat 7
       Finally, run the atmospheric correction (-r for reflectance input map; -a for date >  July
       2000):
       i.atcorr -r -a lsat7_2002_40_rad elevation=elevation parameters=icnd_lsat4.txt output=lsat7_2002_40_atcorr
       Note  that  the  altitude  value  from  ’icnd_lsat4.txt’  file is read at the beginning to
       compute the initial transform. Therefore, it is necessary to provide a value that might be
       the mean value of the elevation model (r.univar elevation). For the atmospheric correction
       per se, the elevation values from the raster map are used.

       Note that the process is computationally intensive. Note also, that i.atcorr reports solar
       elevation angle above horizon rather than solar zenith angle.

REMAINING DOCUMENTATION ISSUES

       The  influence and importance of the visibility value or map should be explained, also how
       to obtain an estimate for either visibility or aerosol optical depth at 550nm.

SEE ALSO

       GRASS Wiki page about Atmospheric correction

        i.aster.toar, i.colors.enhance, i.landsat.toar, r.info, r.mapcalc, r.univar

REFERENCES

           ·   Vermote, E.F., Tanre, D., Deuze, J.L., Herman,  M.,  and  Morcrette,  J.J.,  1997,
               Second simulation of the satellite signal in the solar spectrum, 6S: An overview.,
               IEEE Trans. Geosc. and Remote Sens. 35(3):675-686.

           ·   6S Manual: PDF1, PDF2, and PDF3

           ·   RapidEye sensors have been provided by RapidEye AG, Germany

           ·   Barsi, J.A., Markham, B.L. and Pedelty, J.A., 2011, The operational  land  imager:
               spectral   response   and   spectral   uniformity.,   Proc.   SPIE  8153,  81530G;
               doi:10.1117/12.895438

AUTHORS

       Original version of the program for GRASS 5:
       Christo Zietsman, 13422863(at)sun.ac.za

       Code clean-up and port to GRASS 6.3, 15.12.2006:
       Yann Chemin, ychemin(at)gmail.com

       Documentation clean-up + IRS LISS sensor addition 5/2009:
       Markus Neteler, FEM, Italy

       ASTER sensor addition 7/2009:
       Michael Perdue, Canada

       AVNIR, IKONOS sensors addition 7/2010:
       Daniel Victoria, Anne Ghisla

       RapidEye sensors addition 11/2010:
       Peter Löwe, Anne Ghisla

       VGT1 and VGT2 sensors addition from 6SV-1.1 sources, addition 07/2011:
       Alfredo Alessandrini, Anne Ghisla

       Added Landsat 8 from NASA sources, addition 05/2014:
       Nikolaos Ves

       Geoeye1 addition 7/2015:
       Marco Vizzari

       Worldview3 addition 8/2016:
       Markus Neteler, mundialis.de, Germany

       Sentinel-2A addition 12/2016:
       Markus Neteler, mundialis.de, Germany

       Sentinel-2B addition 1/2018:
       Stefan Blumentrath, Zofie Cimburova, Norwegian Institute for Nature Research, NINA,  Oslo,
       Norway

       Last changed: $Date: 2019-01-21 21:08:55 +0100 (Mon, 21 Jan 2019) $

SOURCE CODE

       Available at: i.atcorr source code (history)

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