Analysis Of Hyperspectral On Flue-cured Tobacco And Its Agricultural Parameter Estimation Under Different Nitrogen Levels

Nitrogen nutrition for flue-cured tobacco growth, yield and quality has an important impact, reasonable providing nitrogen for flue-cured tobacco growth plays a decisive role position.It is very necessary to use hyperspectral remote sensing in the field with non-destructive, rapid, real-time method for monitoring tobacco nitrogen status.This experiment used stepwise regression method to establish the estimation model using ground based remote sensing platform, through the study of different nitrogen level of flue-cured tobacco leaf nitrogen content and correlation of agronomic parameters and spectral reflectance characteristics, analysis of different nitrogen level of Flue-cured Tobacco under the canopy spectral characteristics and agronomic parameters and spectral parameter relationship. The main results were as follows:(1)The hyperspectral reflectance for flue-tobacco canopies was acquired in primary growth stages in order to monitor rape status and diagnose nitrogen. The corresponding first derivate spectra were obtained. The analysis on canopy spectral reflectance and derivate spectra under different cultivars and different growth stages showed that the canopy reflectance for different cultivars had significant change at near infrared band and visible band, respectively. Reflectance at visible region changed not significantly with the increasing nitrogen and increased at near infrared region. Derivate spectra had the trend of shift to long wavelength direction and existed "two peak" phenomena at more significant increase of the nitrogen level. Red edge position of canopy reflectance spectra did not change remarkably with growth stages and nitrogen levels. The area of red edge and red edge increased with the augment of the nitrogen supply almost at all growth stages.(2)Based on the change patterns of leaf area index and fresh matter under different nitrogen rates and growth stages,the relationships of leaf area index and fresh matter to canopy hyperspectral reflectance, the first derivative spectral and hyperspectral index were investigated. And the sensitive spectral parameters and quantitative equations for predicting LAI and fresh matter were established. The results showed that LAI and leaf fresh matter increased at earlier stages, and then decreased a little over growth progress; LAI and fresh matter increasing nitrogen level. Correlation between LAI and. canopy reflectance at single wave band was not significant at visible and positive at near infrared. Correlation between LAI and first derivative spectra at single wave band was significant, negative at visible and positive at near infrared. Stepwise regression models were built for estimating LAI and fresh matter of flue-tobacco, the determination coefficients were0.702 and0.741, respectively.(3)The quantitative relationships of leaf nitrogen status to canopy hyperspectral reflectance, the first derivative spectral and hyperspectral index in different flue-cured tobacco cultivars under different nitrogen levels were investigated, and the sensitive parameters and monitoring equations for leaf nitrogen status determined. The results showed that the leaf nitrogen status, canopy hyperspectral reflectance significantly changed with levels of nitrogen fertilization. spectral diagnosis had a good relationship with leaf nitrogen at766-940nm at all stages. Correlation between leaf nitrogen and first derivative spectra at single wave band was significant, negative at visible and positive at near infrared about705-715nm.Stepwise regression model was built for estimating leaf nitrogen of flue-tobacco,the determination coefficient was0.994.(4)The experiment with flue-cured tobacco cultivars under different nitrogen levels, the flue-cured tobacco leaf pigment concentrations were monitored with hyperspectral remote sensing, and quantitative monitoring models were established. The results showed that the pigment concentrations in flue-cured tobacco leaves increased with increasing N application rate,and differed significantly among test cultivars.With the growth,the relative concentration of chlorophyll a+b varied more obviously than those of chlorophyll b and carotenoid (Car).Correlation between chlorophyll a+b and first derivative spectra at single wave band was not significant. Correlation between chlorophyll a+b and first derivative spectra at single wave band was significant, negative at visible and positive at near infrared about702～756nm,705～721nm and761～762nm,754～760nm and779～787nm, respectively. By stepwise regression equation for estimating pigment contents of flue-cured tobacco,in general, Canopy Chlorophyll a+b with high spectral parameter correlation than the carotenoids and hyperspectral parameter correlation, but this study used on Chl sensitive spectral parameters used to monitor Car information also made a good effect.