Understanding Radiance for UTCI map

@mostapha or @chris

From my understanding of how radiance divides light (from [here]) there is a direct, indirect and a specular component. (btw the link to this pdf on the HB primer doesn’t work)

In the utci thermal map the shortwave MRT delta calculation uses direct, indirect and reflected components. How do these correspond? I.e is reflected in the UTCI component, the specular component of radiance?

I’m trying to understand why my model is overestimating the shortwave MRT delta, and it appears to be either the ground surface material is too reflective (i.e too low solar absorption values) or the radiance parameters aren’t appropriate for the case study and are contributing too much indirect radiation to the shortwave delta.

If i use the highest accuracy radiance param settings (below), with rflux the sw delta is overestimated by about 10°C

-ab 6 -ad 25000 -as 4096 -c 1 -dc 0.75 -dp 512 -dr 3 -ds 0.05 -dt 0.15 -lr 8 -lw 4e-07 -ss 1.0 -st 0.15

If i change -ab to 2, which seems to be the most impactful parameter, i get closer results with the SW Delta overestimated by about 2°C (but less accurate curve compared to measured SW MRT data)