[GRASS-user] global radiation calculated with r.sun seems to be very high

[Hamish]

Hi,

does anyone have the "definitive" way of converting micro-Einsteins (aka
micro-moles of photons) in the PAR part of the spectrum to watts? I assume
you'd have to use the linke factor to estimate how much energy gets through
into the other parts of the full light spectrum as part of the energy integration.

I can figure out a simple method but I wouldn't trust it for definitively
calibrating the model, or at least am always on the lookout for something
better. Ultimately I'd love to be able to use our Li-COR time-series data
to calibrate the r.sun model, producing a local Linke number from sunny day
data and better cloud diffusion coefficients for cloudy ones (deficit from
modeled clear-sky estimate).

at minimum converting a chunk of that uE PAR data it could tell us which
of the two (or both) is right/wrong.


as for the question about hourly integrations, I'm not sure it is possible
without hacking the code. The best you could do is calc instantaneous flux
at the bottom of each hour and (non-correctly) pretend that value is the
average over the whole hour. or just present the instantaneous value at
the top of each value, document it, and leave it at that.


Hamish