Atmospheric transmissivity- Solar Analyst

Discussion created by ampatzi on May 20, 2011
Latest reply on May 23, 2011 by ampatzi
Dear all,

I would appreciate your help on the description of the atmospheric transmissivity parameter used in Topo view/Solar Analyst. In the Help section in ArcGIS 9.3 it is defined as the ratio of global irradiance on earth to extraterrestrial solar radiation in the direction of the zenith. Nevertheless in journal articles referring to the use of Solar Analyst, I have seen it defined as the transmissivity of beam irradiance only (this was my understanding too as it is used only for the calculation of the direct irradiance only), through cloud particles, aerosol particles (natural and artificial) and molecules of gases [calculated as ??=kt (1-kd), where kt is the clearness index and kd the diffuse ratio)).
Which of the two is the correct one for the algorithm employed by the Solar Analyst?
Thank you in advance for any replies.