[GRASS-user] Clarification on units used in r.sun

[Hamish]

Dylan Beaudette wrote:
> 
> I was aware of the Joule - Watt relationship, but was not quite sure
> why r.sun  was using W*h instead of Joules. Since a Mega-Joule is a
> much more readily used unit of enery, I think that I will do the
> conversion from now on.

It is my understanding that W/m2 is the standard unit used by the solar
modelling community.

The other common one that our LI-COR PAR sensors are calibrated with is
micro-mol . s-1 . m-2.  (aka einsteins, or photon quanta)

I suggest having a look through the literature and manuals here:
  http://www.licor.com/env/Products/Sensors/rad.jsp

Starting with:
  http://www.licor.com/env/PDF_Files/Rad_Meas.pdf

It is well written, informative, and clear.


> The next question, pardon my ignorance, is: how to interpret hourly
> averaged insolation (beam + diffuse) values from a weather station,
> which are reported in W/(m^2) ?
>
> Is this essentially this same thing, as it is "integrated" over an
> hour when summed for the entire day?

I would guess sum midnight to midnight hourly averages of W/m2 = mode2 ?


Hamish

ps- I will cc this thread to Jaro