Calculate transmittance / reflectance instead of absolute quantities.
That is, set the extraterrestrial irradiance to 1 and do not correct for Sun-Earth distance:
 |
(0.1) |
where
is the irradiance / actinic flux / radiance and
is the extraterrestrial flux.
Please note the difference to reflectivity.
Arve Kylling
2010-03-10