Modification of vegetation indices based on rice background characteristics

Vegetation indices are widely used in many remote sensing monitoring of vegetation, but vegetation monitoring based on vegetation indices may be affected by variation of soil background, especially for rice which is cultivated in flooded soil. The objective of study is to modify the parameters of a number of background-adjusted vegetation indices with the purpose of more accurately estimating rice agricultural variables which have different backgrounds of various water coupled with different things in suspension. In the study, at the first step, vegetation indices with different parameters, which can reduce the effect of background, were derived from the spectra at different rice development stages. Second, the regression equations between vegetation indices and LAI using different forms were fitted. Finally, the optimal parameters were determined by selecting the highest coefficients of determination of fitted equations in different forms. The results indicated that the parameters of these vegetation indices all should be modified because of the special characteristics of rice background. The modified parameter were α =1.44 for WDVI, L=0.08 for SAVI, θ =0.02 for SAVI2, a =0.5, b=0.02, X =0.02 for TSAVI. In addition, among all the fitted equations taking WDVI, SAVI, SAVI2 and TSAVI as independent variables and LAI as dependent variable, TSAVI gave more accurate estimation than SAVI and SAVI2. WDVI behaved relatively poorly. In all, for remote sensing monitoring of rice, parameter modifications of vegetation indices can improve the monitoring precision.