Calculate transmittance / reflectance instead of absolute quantities. That is, set the extraterrestrial irradiance to 1 and do not correct for Sun-Earth distance:

$\displaystyle T = \frac{E}{E_0}$ (0.1)

where $ E$ is the irradiance / actinic flux / radiance and $ E_0$ is the extraterrestrial flux. Please note the difference to reflectivity.





Arve Kylling 2010-03-10