[GRASS-user] 0-1 scaling of coefdh in r.sun

[Alan Swanson]

Hi list,
New grass user here, impressed with its capabilities and ease of use.

I have a question about coefdh, which scales the diffuse component of
radiation in r.sun.  According to the references (Suri and Hofierka 2004;
Hofierka and Suri 2002), this should be calculated as the ratio of measured
horizontal diffuse radiation to diffuse radiation predicted under clear sky
conditions.  This ratio is supposed to be between 0 and 1, but the
clear-sky diffuse predictions are often smaller than measured values,
resulting in a ratio greater than 1.

What am I missing here?  Under clear sky conditions, isn't diffuse
radiation at its minimum, so that the presence of clouds always results in
a ratio greater than 1?  Am I supposed to truncate at 1, or rescale so that
the max is 1?
Thanks,
Alan
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