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

[Dylan Beaudette]

On 11/30/06, Hamish <hamish_nospam at yahoo.com> wrote:
> 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 ?
>

Right-- this was what I had been *assumming* unitl now :)
... but after getting some odd results I decided to ask around.

With respect to a previous email about odd results from r.sun : I
think that was caused by an operator error, and will post a reply to
myself in order to clear Jaro, et al. :) .

Dylan