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

Salvatore Mellino salvatore.mellino at gmail.com
Sat Sep 10 12:31:32 EDT 2011

Thanks Hamish,

how can I read the r.sun code?

I want to know if albedo effect is added or subtracted to global radiation calculation…or it is not computed…
What do you think about the following expression?

available_rad= beam_rad + diffuse_rad - reflected_rad

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

I want to know the available radiation  that should be global radiation minus the radiation that was reflected by atmosphere and ground. Only the radiation that which is not reflected drives terrestrial, oceanic and atmospheric processes.

Il giorno 09/set/2011, alle ore 02:18, Hamish ha scritto:

> 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...
> Hamish

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