Comparison of four methods for estimating leaf area index based on terrestrial three-dimensional laser scanning

摘要

The leaf area index (LAI) of 16 sample plots was estimated based on terrestrial three-dimensional laser scanning. The point-cloud data of stand canopy were first scaled and projected onto a hemisphere according to Lambert azimuthal equal-area projection or stereo-graphic projection, and the resulting hemispherical point-cloud images were used to extract the canopy porosity coefficients. Then, single-angle inversion and Miller formula inversion methods were used, respectively, to calculate the effective leaf area indices with canopy porosity coefficients. Results showed that the effective LAIs estimated by single-angle inversion method with Lambert projection and stereographic projection were within the range of 2.14-5.36 and 1.83~4.67, respectively.The effective LAIs obtained by Miller formula inversion method with Lambert projection and stereographic projection were within the range of 1.84~4.67 and 1.68-4.34, respectively. As a comparison, the LAI measured with a fish-eye camera ranged from 1.55to 3.87. The LAI values estimated with four different calculation methods were linearly correlated with those measured by a fish-eye camera. The highest coefficient of determination (ft2) 90.28% was obtained by the Miller formula inversion method combined with stereographic projection, and Duncan's new multiple range test also further showed that this method had a relatively higher precision compared to other three methods.