[GRASS-user] Use of coefbh and coefdh in r.sun

[Dylan Beaudette]

Hi,

After consulting with an atmospheric scientist, I have decided that it might 
be simpler to estimate 'real-sky' radiance as opposed to trying to estimate 
the Linke turbidity for the estimation of 'clear-sky' conditions. 

It looks like r.sun can use input maps: coefbh and coefdh to compute real-sky 
radiance values. I would like to be sure that I am interpreting these inputs 
correctly:

1. does (1- coefbh) = coefdh ?
2. does coefdh correspond to the notion of the 'diffuse fraction' which is 
commonly calculated via something called the 'clearness index' ?


If this is the case, then it is not all that difficult to compute coefdh from 
pyranometer data and the output from r.sun (mode 1)

I will update the man page with my approach, if these assumptions are correct.

cheers,

PS:
a relevent references is:

Jacovides, C.; Tymvios, F.; Assimakopoulos, V. & Kaltsounides, N. Comparative 
study of various correlations in estimating hourly diffuse fraction of global 
solar radiation. Renewable Energy, 2006, 31, 2492 - 2504


-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341