Geografic-Information-System/raster/r.sunhours/r.sunhours.html

<h2>DESCRIPTION</h2>

<em>r.sunhours</em> calculates sun elevation and sun azimuth angles for
the given time of day and each grid cell in the current region. 
Additionally, the photoperiod (sunshine hours) can be calculated.

<p>
Sun elevation, height, height angle, or solar altitude angle is the
angle in degrees between the horizon and a line that points from the
site towards the centre of the sun.
<p>
The sun azimuth angle is here defined as the azimuth angle in degrees
of the sun from due north in a clockwise direction.
<p>
The time used here is defined such that 12:00 (high noon) is the time
when the sun has reached its highest point in the sky at the current site,
unless the <em>-t</em> flag is used in which case time is interpreted as 
Greenwich standard time.
<p>
If a <em>sunhour</em> output map is specified, the module calculates 
sunshine hours for the given day. This option requires both Greenwhich 
standard time (<em>-t</em> flag) and the solpos algorithm of NREL 
(<em>-s</em> flag).

<h2>EXAMPLES</h2>

Calculate sun's elevation angle map for 2010-10-11 at 14:00h solar time:
<div class="code"><pre>
r.sunhours elevation=sun_elev year=2010 month=10 day=11 hour=14 minute=00
</pre></div>
<p>

Calculate photoperiod of day of year 1 (1st January) 2012
<div class="code"><pre>
r.sunhours -s sunhour=photoperiod_doy_001 year=2012 day=1
</pre></div>

<h2>Acknowledgements</h2>
Acknowledgements: National Renewable Energy Laboratory for their
<a href="http://rredc.nrel.gov/solar/codesandalgorithms/solpos/">SOLPOS 2.0</a> sun position
algorithm.

<h2>SEE ALSO</h2>
<em>
<a href="g.region.html">g.region</a>,
<a href="r.sun.html">r.sun</a>,
<a href="r.sunmask.html">r.sunmask</a>,
</em>

<h2>AUTHOR</h2>

Markus Metz

<p><i>Last changed: $Date$</i>