Inversion of the severity of winter wheat yellow rust using proper hyper spectral index

The objective of this study was to develop the appropriate spectral indices for prediction of yellow rust index that are relatively insensitive to species, canopy structures (such as leaf area index and leaf angle distributions), foliar inner structures, and soil condition variations. When winter wheat was infected with yellow rust, the leaf chlorophyll concentration decreased, the regression equation between SPAD value and measured chlorophyll concentration was established. Canopy reflected spectrum and canopy chlorophyll concentration were measured during growth duration, it indicated that it had the logarithmic relationship between the ratio of Transformed Chlorophyll Absorption in Reflectance Index (TCARI) to Optimized Soil Adjusted Vegetation Index (OSAVI) and Minolta Chlorophyll Meter (SPAD) value, with a coefficient of determination R²=0.7795(n=320), so the combined index TCARI/OSAVI was proved to be sensitive to chlorophyll concentration and very resistant to the other variations such as Leaf Area Index(LAI) and no photosynthetic materials at canopy level. Therefore, the predictive capability of TCARI/OSAVI seems consistent and satisfactory. The proper reflectance index of photochemical reflectance index (PRI) was chosen for disease index inversion by minimizing foliar inner structure effect, it has linear negative relationship between the normalized photochemical reflectance index(NPRI) and disease index(DI), with a coefficient of determination R²=0.8477(n=63), so the normalized photochemical reflectance index(NPRI) can be used to monitor the disease index of yellow rust.