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Hemispherical photography simulations with an architectural model to assess retrieval of leaf area index

Three-dimensional simulations of forest scenes rendered with the freeware POV-Ray ( used to assess retrievals of plant and leaf area index (PAI and LAI) from hemispherical photography(HP). Ten HPs were simulated in 75 scenes with random, erectophile and planophile leaf
angle distri-butions. PAI retrieved using Beer's law near 57.3?(55-60?) and with the truncated Miller integrationover zenith angles from 10?to 65?gave similar results. The importance of clumping was also shown toobtain accurate PAI. Foliage density inside the crown was a major factor causing
underestimates of thePAI because the clumping effect was underestimated. Moreover, best PAI retrievals were found with theclumping index method using the Chen and Cihlar method combined with the Lang and Xiang method(relative RMSE of 23-24% and relative median absolute error of 12-14%) and was
slightly less affected bythe averaging length when compared with only using the Lang and Xiang. Previous error measurementsof 29% were reduced to 16-23% for a black spruce stand using updated input variables and the methodpresented here, and they were shown to fall within the errors of the
simulation framework.

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