.TH i.emissivity 1grass "" "GRASS 8.2.1" "GRASS GIS User's Manual"
.SH NAME
\fI\fBi.emissivity\fR\fR  \- Computes emissivity from NDVI, generic method for sparse land.
.SH KEYWORDS
imagery, emissivity, land flux, energy balance
.SH SYNOPSIS
\fBi.emissivity\fR
.br
\fBi.emissivity \-\-help\fR
.br
\fBi.emissivity\fR \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of the NDVI map [\-]
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of the output emissivity layer
.SH DESCRIPTION
\fIi.emissivity\fR 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).
.PP
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).
.PP
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.
.SH REFERENCES
.RS 4n
.IP \(bu 4n
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)
.IP \(bu 4n
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.
.IP \(bu 4n
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.
.RE
.SH SEE ALSO
\fI
i.eb.netrad
\fR
.SH AUTHOR
Yann Chemin, GRASS Development Team
.SH SOURCE CODE
.PP
Available at:
i.emissivity source code
(history)
.PP
Accessed: Sunday Jan 22 07:37:27 2023
.PP
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.PP
© 2003\-2023
GRASS Development Team,
GRASS GIS 8.2.1 Reference Manual