1r.sunhours(1) GRASS GIS User's Manual r.sunhours(1)
2
6 r.sunhours - Calculates solar elevation, solar azimuth, and sun hours.
7 Solar elevation: the angle between the direction of the geometric cen‐
8 ter of the sun’s apparent disk and the (idealized) horizon. Solar az‐
9 imuth: the angle from due north in clockwise direction.
10
12 raster, solar, sun energy, sun position
13
15 r.sunhours
16 r.sunhours --help
17 r.sunhours [-ts] [elevation=name] [azimuth=name] [sunhour=name]
18 year=integer [month=integer] day=integer [hour=integer]
19 [minute=integer] [second=integer] [--overwrite] [--help] [--ver‐
20 bose] [--quiet] [--ui]
21 Flags:
23 -t
24 Time is local sidereal time, not Greenwich standard time
25 -s
27 Do not use SOLPOS algorithm of NREL
28 --overwrite
30 Allow output files to overwrite existing files
31 --help
33 Print usage summary
34 --verbose
36 Verbose module output
37 --quiet
39 Quiet module output
40 --ui
42 Force launching GUI dialog
43 Parameters:
45 elevation=name
46 Output raster map with solar elevation angle
47 Name for output raster map
48 azimuth=name
50 Output raster map with solar azimuth angle
51 Name for output raster map
52 sunhour=name
54 Output raster map with sunshine hours
55 Sunshine hours require SOLPOS use and Greenwich standard time
56 year=integer [required]
58 Year
59 Options: 1950-2050
60 month=integer
62 Month
63 If not given, day is interpreted as day of the year
64 Options: 1-12
65 day=integer [required]
67 Day
68 Options: 1-366
69 hour=integer
71 Hour
72 Options: 0-24
73 Default: 12
74 minute=integer
76 Minutes
77 Options: 0-60
78 Default: 0
79 second=integer
81 Seconds
82 Options: 0-60
83 Default: 0
84
86 r.sunhours calculates sun elevation and sun azimuth angles for the
87 given time of day and each grid cell in the current region. Addition‐
88 ally, the photoperiod (sunshine hours on flat terrain) can be calcu‐
89 lated.
90 Sun elevation, height, height angle, or solar altitude angle is the an‐
92 gle in degrees between the horizon and a line that points from the site
93 towards the centre of the sun.
94 The sun azimuth angle is here defined as the azimuth angle in degrees
96 of the sun from due north in a clockwise direction.
97 The time used here is defined such that 12:00 (high noon) is the time
99 when the sun has reached its highest point in the sky at the current
100 site, unless the -t flag is used in which case time is interpreted as
101 Greenwich standard time.
102 If a sunhour output map is specified, the module calculates sunshine
104 hours for the given day. This option requires both Greenwhich standard
105 time and the use of the SOLPOS algorithm by NREL.
106
108 To consider also cast shadow effects of the terrain, r.sun has to be
109 used.
110
112 Calculating a sun elevation angle map
113 Calculate the sun elevation angle map for 2010-10-11 at 14:00h solar
114 time:
115 # set computational region to North Carolina state extent
116 g.region n=318500 s=-16000 w=124000 e=963000 res=500 -p
117 r.sunhours elevation=sun_elev year=2010 month=10 day=11 hour=14 minute=00
118 # visualize
119 d.mon wx0
120 d.rast sun_elev
121 d.vect nc_state type=boundary
122 d.legend sun_elev -s
123 Sun angle map (in degree) of North Carolina for the 2010-10-11 at
125 14:00h solar time
126 Calculate map of photoperiod (insolation time)
128 Calculate photoperiod of day-of-year 001 (1st January) of 2012 for the
129 current computational region, ignoring cast shadow effects of the ter‐
130 rain:
131 g.region -p
132 r.sunhours sunhour=photoperiod_doy_001 year=2012 day=1
133
135 Acknowledgements: National Renewable Energy Laboratory for their SOLPOS
136 2.0 sun position algorithm.
137
139 g.region, r.sun, r.sunmask
140
142 Markus Metz
143
145 Available at: r.sunhours source code (history)
146 Accessed: Saturday Oct 28 18:18:00 2023
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151 © 2003-2023 GRASS Development Team, GRASS GIS 8.3.1 Reference Manual
153GRASS 8.3.1 r.sunhours(1)