i.emissivity manual: sync to trunk

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@68627 15284696-431f-4ddb-bdfa-cd5b030d7da7

imagery/i.emissivity/i.emissivity.html

@@ -2,18 +2,44 @@
 
 <em>i.emissivity</em> calculates the emissivity in the longwave radiation
 spectrum, according to the semi-empirical equation related to NDVI by
-Caselles and Colles (1997), valid in the NDVI range of 0.16 to 0.74.
+Caselles et al. (1997), valid in the NDVI range of 0.16 to 0.74 (Bastiaanssen, 1995).
 <p>
-Estimation in the 8-14 micrometers range for sparse canopy...
-<!-- TODO: incomplete phrase! -->
+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). 
+<p>
+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.
 
 <h2>SEE ALSO</h2>
 
 <em>
-<a href="i.eb.netrad.html">i.eb.netrad</a><br>
+<a href="i.eb.netrad.html">i.eb.netrad</a>
 </em>
 
-<h2>AUTHORS</h2>
+<h2>REFERENCES</h2>
+
+<ul>
+<li> Bastiaanssen, W.G.M., 1995.
+  Estimation of Land surface parameters by remote sensing under clear-sky
+  conditions. PhD thesis, Wageningen University, Wageningen, The Netherlands.
+  (<a href="http://edepot.wur.nl/206553">PDF</a>)</li>
+<li> 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.</li>
+<li> Rubio, E., V. Caselles, and C. Badenas, 1997.
+  Emissivity measurements of several soils and vegetation types in the
+  8-14 &micro;m wave band: Analysis of two field methods. Remote Sensing of
+  Environment 59(3): 490-521.
+</ul>
+
+<h2>AUTHOR</h2>
+
 Yann Chemin, GRASS Development Team<br>
 
 <p><i>Last changed: $Date$</i>