Provided by: grass-doc_7.8.2-1build3_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. *

       30                                                           Worldview4                                                   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)

       204                                                          Worldview4 Pan band (424nm - 842nm)

       205                                                          Worldview4 Blue band (416nm - 567nm)

       206                                                          Worldview4 Green band (488nm - 626nm)

       207                                                          Worldview4 Red band (639nm - 711nm)

       208                                                          Worldview4 NIR1 band (732nm - 962nm)

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
       Lλ = ((LMAXλ - LMINλ)/(QCALMAX-QCALMIN)) * (QCAL-QCALMIN) + LMINλ
       where,

           ·   Lλ = 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;

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

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

           ·   QCALMIN = the minimum quantized calibrated pixel value (corresponding to LMINλ) in
               DN;

           ·   QCALMAX = the maximum quantized calibrated pixel value (corresponding to LMAXλ) in
               DN=255.
       LMINλ  and  LMAXλ  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

       Worldview4 addition 12/2018:
       Markus Neteler, mundialis.de, Germany

SOURCE CODE

       Available at: i.atcorr source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual