Effects Of Leaf Wax On Estimation Of Chlorophyll Content With Vegetation Indices

Chlorophyll is an important index to the green vegetation health. There have been a lotof researches focusing on the estimation of chlorophyll content by creating high spectralvegetation indices. However, the vegetation indices may be affected by the leaves tablestructure, and impacting the accuracy of estimation on chlorophyll content. This researchselected five vegetation species （Syringaspp, Ligustrum vicaryi, Ginkgo biloba, Paeoniasuffruticosa, Nelumbo mucifera） as samples. The leaf samples were taken ten times throughthe growing season during five months （May to September）. The leave reflectance weremeasured before and after the leaf surface wax removal, and they were compared with thechlorophyll content to estimate the impact of the leaf surface wax on the accuracy ofestimating leaf chlorophyll content. The studies revealed that:1. Vegetation leaves reflectrance decreased after the removal of surface wax in differentwavelegth through400-2400nm. Most vegetation indices before and after the removal ofthe wax has a lot of changes, and the vegetation indices which changed less than5%areR₆₇₂/R₅₅₀,R₈₆₀/R₅₅₀, SIPI, WBI, PSNDa1, PSNDa2, RARSa₂, RARSa₃, RARSa₄, REP and(R₅₄₂-Rmin_red)/(R₇₅₀-Rmin_red). This result revealed that these vegetation indices isrelatively not sensible to the leaves surface wax;2.72vegetation indices and chlorophyll content were compared in the correlation analysis.It is found that vegetation indices R₆₇₂/R₅₅₀, R₅₅₀/R₈₀₀, R₈₀₀/R₅₅₀, R₈₆₀/R₅₅₀,1/R₅₅₀-1/R₇₅₀,R₆₇₂/(R₅₅₀×R₇₀₈, GM1, NDVI,(R₅₄₂-Rmin_red)/(R₇₅₀-Rmin_red) were relatively robustbecause the correlation coeffient between them were high and did not change so muchbefore and after the removal of wax. these vegetation indices are more suitable for leafchlorophyll inversion in the leaf wax coverd vegetation;3. We have used the emprical formula which were reported in the literatures to estimatedthe chlorophyll content by the vegetation indices before and after the leaf surface waxremoval. The results revealed that the vegetation indices1/R₅₅₀-1/R₇₅₀, GM1:R₇₅₀/R₅₅₀werethe most robust, since the correlation coefficients were relatively high and the slope of thefitted line were close to1before and after the leaf wax removel, when we tested theestimation accuracy using half of our leaf samples. We conclued these indices may be themost wax-insensitive vegetation indices to estimate leaf chlorophyll content.