NAME

       i.emissivity  - Computes emissivity from NDVI, generic method for sparse land.

KEYWORDS

       imagery, emissivity, land flux, energy balance

SYNOPSIS

       i.emissivity
       i.emissivity --help
       i.emissivity  input=name  output=name   [--overwrite]   [--help]   [--verbose]   [--quiet]
       [--ui]

   Flags:
       --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 the NDVI map [-]

       output=name [required]
           Name of the output emissivity layer

DESCRIPTION

       i.emissivity calculates the emissivity in the longwave radiation  spectrum,  according  to
       the  semi-empirical  equation related to NDVI by Caselles et al. (1997), valid in the NDVI
       range of 0.16 to 0.74 (Bastiaanssen, 1995).

       Caselles et al. (1997) give reference (in Table 3 and Figure 2) to  both  the  NDVI  range
       used (0.15 - 0.71) and the corresponding emissivity range used (0.97 - 0.99).

       The  emissivity  is the efficiency of longwave energy returning to the atmosphere from the
       skin surface. The skin surface receives heat from the thermal infrared  radiation  of  the
       Sun,  through  atmospheric  interaction.  A part is returned to the atmosphere fastly, and
       another part is kept in the surface skin to be returned later. In more  scientific  terms,
       the grey body radiation is equal to the black body radiation times the emissivity.

SEE ALSO

        i.eb.netrad

REFERENCES

           •   Bastiaanssen,  W.G.M.,  1995.   Estimation  of  Land  surface parameters by remote
               sensing under clear-sky conditions. PhD thesis, Wageningen University, Wageningen,
               The Netherlands.  (PDF)

           •   Caselles,  V.,  C.  Coll,  and  E.  Valor,  1997.   Land  surface  emissivity  and
               temperature  determination  in  the  whole  HAPEX-Sahel  area  from  AVHRR   data.
               International Journal of Remote Sensing 18(5):1009-1027.

           •   Rubio,  E., V. Caselles, and C. Badenas, 1997.  Emissivity measurements of several
               soils and vegetation types in the  8-14  µm  wave  band:  Analysis  of  two  field
               methods. Remote Sensing of Environment 59(3): 490-521.

AUTHOR

       Yann Chemin, GRASS Development Team

SOURCE CODE

       Available at: i.emissivity source code (history)

       Accessed: unknown

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