Leaf Area Index Estimation of Spring Maize with Canopy Hyperspectral Data Based on Linear Regression Algorithm

Based on the leaf area index (LAI) and canopy hyperspectral data during growing season of spring maize under different soil moisture conditions in Jinzhou, Liaoning province in 2013, the relationship between LAI and the characteristics of canopy hyperspectral in different development periods with different growth status were analyzed. Canopy spectral reflectance, its logarithm of the reciprocal and its first derivative in 350 similar to 2 500 nm of 313 valid data sets were collected and calculated, after rejecting the bands which were serious influenced by the atmospheric water content. Multivariate step linear regression (MSLR) and partial least squares regression (PLS) were used as the dimensionality reduction methods to establish the maize LAI models, and the models precision were compared and tested respectively. The results show that, the LAI of spring maize has significant negative correlation with the spectral reflectance of visible band (350 similar to 680 nm), and infrared band (1 430 similar to 1 800 and 1 950 similar to 2 450 nm), but it has significant positive correlation with the logarithm of the reflectance reciprocal in these bands. The reflectance first derivative and LAI have significant positive correlation bands in visible band and infrared band (350 similar to 1 350 nm). Linear regression algorithm of spring maize LAI with the whole band of hyperspectral data, using PLS with the spectral reflectance as the independent variable to establish the LAI model, the fitting degree is better than that of MSLR; the root mean square error (RMSE) is 0.480 7, and using MSLR with the logarithm of the reflectance reciprocal and the reflectance first derivative as the independent variable, have better fitting degree than that of PLS, the RMSE are 0.333 5 and 0.348 8 respectively. Use MSLR with the logarithm of the spectral reflectance reciprocal as the independent variable to establish the maize LAI model, the fitting degree is better in the three canopy hyperspectral data of spring maize of the two regression algorithm.