Red edge characteristics and leaf area index estimation model using hyperspectral data for rape

The hyperspectral reflectances for rape canopies consisting of five cultivars and three nitrogen levels were measured in 2003～2004 growth period by an ASD FieldSpec Pro FR^TM. The corresponding leaf area indices were observed. The red edge parameters were extracted using the spectral reflectances of the rape canopies. There exist ‘two peak’ phenomena for the red edge of rape canopy spectra. The position of red edge λ_red is located between 690 nm and 720 nm. There is a ‘platform of red edge’ at the bloom stage of rape. The red edge shift was detected before flowering stage and blue shift after flowering stage. The relationship between red edge parameters and the leaf area index(LAI) was investigated during 8 development periods. Results were not consistently significant at any wavelengths. The leaf area indices were significantly correlative to the red edge parameters λ_red, Dλ_red and S_red of the canopy spectra before flowering stage, whereas the correlation coefficient showed very low r values that were in significant after flowering stage. So the red edge parameters of rape canopies before the flowering stage can be used to estimate the leaf area indices. The results for different stages, linear and non-linear regression models were compared and the optimum model for LAI before flowering stage was recommended.