Evaluation of hemispherical photography for determining the short and longwave radiation balance below forest canopies

Hemispherical photographs are regularly used to determine canopy leaf area. Accurate determination of the radiation balance below forest canopies is required for calculations of snow melt and below canopy photosynthesis. Measurements of above and below canopy short and longwave radiation were used to evaluate the accuracy of hemispherical photographs and analysis software to aid in the determination of these fluxes. A Kipp and Zonen CNR1 below the canopy and a CNR1 or pyrgeometer and pyranometer above the canopy were used to measure these fluxes. Above canopy diffuse radiation was measured or calculated. Measurements were made in 6 lodgepole pine stands ranging from burnt, young to mature conditions. There was good agreement between the measured and calculated solar transmissivity and longwave view factors.