Using new hyperspectral index to estimate leaf chlorophyll content in winter wheat

Leaf chlorophyll content is a key indicator of crop photosynthesis activity, which is correlated with leaf nitrogen concentration, and can serve nitrogen fertilizer decision-making. So it is of significant to estimate chlorophyll content for crop growth diagnosis. In this study, a new hyperspectral index was proposed to estimate leaf chlorophyll content in winter wheat. Hyperspectral reflectance data, covering bands from 350 to 2500nm, were collected using a ground-based ASD spectrometer on winter wheat at different stages from 2008 in rural fields of Beijing, China. Leaf chlorophyll content was obtained by traditional laboratory methods on the same area. First, hyperspectral reflectance data from 400 to 1300nm were normalized, and then a new spectral index, symbolized k_nir, was proposed by a mean of fitting the normalized reflectance ranging from 760 to 920nm to evaluate chlorophyll content in winter wheat in comparison with some existing typical indices. The analysis results showed that k_nir was the best index for assessing chlorophyll comparing with the existing indices, with R² value of 0.51. It indicates that the new spectral index has a good potential for estimating chlorophyll in winter wheat.