Difference in Diffuse Site Factors Due to Spatial Distribution of Sky Luminance

概要

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The difference in estimation of the diffuse site factor due to different models of the spatial distribution of sky luminance was examined. The examined models were the uniform overcast sky (UOC) and standard overcast sky (SOC). The difference between the diffuse site factors for UOC (Ψ_<UOC>) and for SOC (Ψ_<SOC>) was 1.5% in average and ranged from -0.4% to 5.2%. A strongly positive correlation was observed between Ψ_<UOC> and Ψ_<SOC>:Ψ_<SOC>=1.109Ψ_<UOC> (n=270, r=0.999, p<0.001). This shows that Ψ_<SOC> tends to be larger than Ψ_<UOC>, and the difference increases with the increase in Ψ_<UOC> or Ψ_<SOC>. The difference is determined by three factors: 1) the decrease in gap fraction (gap ratio) with zenith angle; 2) the incident angle of cosine law; 3) the difference in spatial distribution of sky luminance.
森林計画学会の論文