[GRASS-user] solar exergy (r.sun)

Hamish hamish_b at yahoo.com
Thu Sep 8 20:18:11 EDT 2011

Salvatore wrote:
> I generate 2 maps with r.sun (1 Jan), the first one setting
> albedo=0, and the second one setting albedo=2.0 but I
> received the same values (look at statistics calculated by
> r.univar). Why?

beam_rad only gives you the available incident radiation, not the
absorption. As I understand it, albedo is used in the reflection
maps in hilly terrain.

> My goal is to generate a map for the exergy (available
> energy) of solar radiation, so I need a map without diffuse
> and reflected radiation. Is it correct to use r.sun and as
> output beam_rad or global_rad? and if I set the albedo to
> 2.0, is this effect added to the irradiation or is it
> subtracted? I hope I was clear…

if you want to know all incoming radiation, use the global sum.

if you have a very reflective steep hillside positioned to
reflect light back on your study site, the reflected radiation
map should go up. I'm not sure if that 20% is removed from the
steep hillside's value, or if that just stays as available
incident light.

further experimentation &/or reading the code would be needed
to say for sure...


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