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i.emissivity.1grass - Man Page

Computes emissivity from NDVI, generic method for sparse land.


imagery, emissivity, land flux, energy balance


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



Allow output files to overwrite existing files


Print usage summary


Verbose module output


Quiet module output


Force launching GUI dialog


input=name [required]

Name of the NDVI map [-]

output=name [required]

Name of the output emissivity layer


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



Yann Chemin, GRASS Development Team

Source Code

Available at: i.emissivity source code (history)

Accessed: Tuesday May 14 13:41:42 2024

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