[Method of Background Elimination for Wheat Leaves Based on the BPLT Model].

In order to precisely acquire leaf reflectance spectra (400-1 000 nm), influence of background on leaf reflectance spectra was studied. Experiment was conducted to discriminate the characteristics of wheat leaves based on 8 background materials and leaf chlorophyll concentration. BPLT (Background Plate) model, based on the Plate model, was promoted and applied to remove the influence of leave background. The BPLT model needed "2-3-1"variables, which were input variables R0 (reflectance of the interaction of leaves and background), σ(reflectance of background alone), intermediate variables R12 (reflectance of interacting interface from air to a compact leaf), R21 (reflectance of interacting interface from a compact leaf to air), τ (the transmissivity of the plate), and ultimate variable R (reflectance of a compact leaf alone). To verify this model, Analysis of Variance (ANOVA) was conducted to compare ten vegetation indices under different background influences. The results indicated that percent of variation in background reflectance associated with spectral vegetation indices was 5% lower after using the BPLT model. Meanwhile, wheat leaf chlorophyll concentration at different levels could be effectively estimated by the means of BPLT model with determined coefficients (DC) greater than 0.9 and residual sum of squares (SSE) less than 1. As with the ANOVA, vegetation indices NIX and MCARI were better than the other 8 ones. The slope of NDI&-MCARI plotted as a function of mean wheat leaf chlorophyll concentration. R2 ranged from 0.847 8 to 0.977 8 with the applied method of BPLT model. The BPLT model is a powerful and accurate method for the acquisition of wheat leaf reflectance information.