NAME
r.sun.angle - Calculates solar elevation, solar azimuth, and sun hours.
Solar elevation: the angle between the direction of the geometric center of the sun's apparent disk and the (idealized) horizon. Solar azimuth: the angle from due north in clockwise direction.
KEYWORDS
raster
SYNOPSIS
r.sun.angle
r.sun.angle help
r.sun.angle [-ts] [elevation=name] [azimuth=name] [sunhour=name] year=integer [month=integer] day=integer [hour=integer] [minute=integer] [second=integer] [--overwrite] [--verbose] [--quiet]
Flags:
- -t
- Time is local sidereal time, not Greenwich standard time
- -s
- Do not use solpos algorithm of NREL
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- elevation=name
- Output raster map with solar elevation angle
- Name for output raster map
- azimuth=name
- Output raster map with solar azimuth angle
- Name for output raster map
- sunhour=name
- Output raster map with sunshine hours
- Sunshine hours require solpos and Greenwich standard time
- year=integer
- Year
- Options: 1950-2050
- month=integer
- Month
- If not given, day is interpreted as day of the year
- Options: 1-12
- day=integer
- Day
- Options: 1-366
- hour=integer
- Hour
- Options: 0-24
- Default: 12
- minute=integer
- Minutes
- Options: 0-60
- Default: 0
- second=integer
- Seconds
- Options: 0-60
- Default: 0
DESCRIPTION
r.sun.angle 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.
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.
The sun azimuth angle is here defined as the azimuth angle in degrees
of the sun from due north in a clockwise direction.
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 -t flag is used in which case time is interpreted as
Greenwich standard time.
If a sunhour output map is specified, the module calculates
sunshine hours for the given day. This option requires both Greenwhich
standard time (-t flag) and the solpos algorithm of NREL
(-s flag).
EXAMPLES
Calculate sun's elevation angle map for 2010-10-11 at 14:00h solar time:
r.sun.angle elevation=sun_elev year=2010 month=10 day=11 hour=14 minute=00
Calculate photoperiod of day of year 1 (1st January) 2012
r.sun.angle -s sunhour=photoperiod_doy_001 year=2012 day=1
AUTHOR
Markus Metz
Last changed: $Date$
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