Winter Wheat

Spectral index method was widely applied to the inversion of crop chlorophyll content. In this study, PSR3500 spectrometer and SPAD-502 chlorophyll fluorometer were used to acquire the spectrum and relative chlorophyll content (SPAD value) of winter wheat leaves on May 2nd 2013 when it was at the jointing stage of winter wheat. Then the measured spectra were resampled to simulated TM multispectral data and Hyperion hyperspectral data respectively, using the Gaussian spectral response function. We chose four typical spectral indices including Normalized Difference Vegetation Index (NDVI), Triangle Vegetation Index (TVI), the ratio of Modified Transformed Chlorophyll Absorption Ratio Index(MCARI) to Optimized Soil Adjusted Vegetation Index(OSAVI) (MCARI/OSAVI) and Vegetation Index Based on Universal Pattern Decomposition Method (VIUPD), which were constructed with the feature bands sensitive to the vegetation chlorophyll. After calculating these spectral indices based on the resampling TM and Hyperion data, the regression equation between spectral indices and chlorophyll content was established. For TM, the result indicates that VIUPD has the best correlation with chlorophyll (R2=0.8197) followed by NDVI (R2=0.7918), while MCARI/OSAVI and TVI also show a good correlation with R2 higher than 0.5. For the simulated Hyperion data, VIUPD again ranks first with R2=0.8171, followed by MCARI/OSAVI (R2=0.6586), while NDVI and TVI show very low values with R2 lesser than 0.2. It is demonstrated that VIUPD has the best accuracy and stability to estimate chlorophyll of winter wheat whether using simulated TM data or Hyperion data, which reaffirms that VIUPD is comparatively sensor independent.

Authors: Jiang Hai-ling, Zhang Li-fu, Yang Hang, Chen Xiao-ping, Wang Shu-dong, Li Xue-ke, Liu Kai

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