Estimation of leaf area index, leaf angle distribution and clumping index with hemispherical photography: Comparison of different algorithms
Leaf area index, leaf angle distribution and clumping index are considered as the most important parameters to characterize the structure of vegetation canopy and model the photosynthesis of vegetation. Although hemispherical photography is widely used to measure those parameters on ground, there are a number of certainties with this method. This study is attempting to answer the following questions: what is difference between automatic thresholding algorithms? How do the techniques used to calculate canopy structure parameters perform?
In this study, 10 hemispherical photographies, which were taken at ten locations along a gradient of canopy closure in Xishuangbanna Tropical Botanical Garden, Yunnan, China (UTM/WGS 84: 47N 732940 E, 2426540 N), are used to estimate leaf area index, leaf angle distribution and clumping index with different automatic thresholding algorithms and different resolution techniques.
The impact of thresholding algorithms on binarization are quite small. Non-linear method performed best for the estimation of leaf area index. Beta function is the better choice for estimating leaf angle distribution although one more unknown is introduced. The log-average method is necessary for the estimation of clumping index. This study will enhance our understanding about the performance of different algorithms for processing hemispherical photography and retrieving the parameters of canopy structure.