Test of accuracy of LAI estimation by LAI-2000 under artificially changed leaf to wood area proportions

The accuracy of LAI-2000 Plant Canopy Analyzer for leaf(LAI) and plant (PAI ) area indexes measurements was tested in 20-year-old Norway spruce stand u sing the reduction of canopy biomass. Needle and branch areas were reduced progressively upward every one meter. Values of effective leaf area index ( LAI(e)), as an uncorrected product of LAI-2000, were compared with directly estimated LAI and PAI values after each reduction step. LAI-2000 underesti mates PAI and LAI values according to LAI-2000 rings readings, and varied p roportions between leaf and wood areas. The values of LAI(e) have been incr eased with decreasing of the view angle of the relevant LAI-2000 rings. The refore, the underestimation of LAI becomes smaller when the readings near t he horizon are masked. More accurate results, for projected LAI (LAI(p)) ca lculation, are produced by LAI-2000 when some dense grids of measurement po ints and the most vertical ring readings (0 - 13 degrees) are used. Correct ion factor 1.6 is possible to use for unreduced canopy hemi-surface LAI est imation, when the last rings (i.e. 5(th) and 4(th) rings, 47 - 74 degrees) are excluded. Correction factor of 1.25 can be used to compute LAI(p) if th e angle readings under 43 degrees are also masked.