Leaf Area Index And Chlorophyll Inversion Of Maize Based On PROSAIL Model

This experiment was conducted in Qinan village,Liangshan town,Yongshou county,Shaanxi province.Through different water and fertilizer treatments in different plots,a total of 31 plots were set up for control test,and four experiments were carried out on maize in the tasseling stage of the jointing stage and the milk ripening stage.Chlorophyll meter using the related test equipment,spectrometer for the growth period of maize parameters,such as access,preliminary data on the fourth stage of corn to analyze characteristics of chlorophyll content and leaf area index,in different growth period of the measured parameter data and prior knowledge of predecessors PROSAIL model,build a model to global and local sensitivity analysis,the model before EFAST method was mainly used in the software MATLAB2017b and Simlab2.2implementation.Then the simulated spectral reflectance is compared with the measured spectral reflectance and the error analysis is carried out.The error correction of the simulated spectral reflectance is established,the polynomial function of linear function and the regression equation of power function are established,and the modeling accuracy of the model is verified and corrected.Finally,atmospheric correction and radiometric correction were carried out by using LANDSAT8 images,and the corresponding corn parameters were found in the lookup table of spectral reflectance and measured parameters calculated by constructing the relevant cost function,and then the inversion modeling of chlorophyll content and leaf area index was carried out to evaluate the accuracy.(1)By analyzing the different characteristics of SPAD value and leaf area index of Maize in four growth periods,it is concluded that the leaf area index and SPAD value increase first and then decrease with the change of growth period.This is because the maize grows high and the leaf area increases continuously from the jointing period to the milk maturity period,which makes the corresponding parameters also increase,after entering the maturity period.The growth of corn is mature,and the leaves begin to turn yellow and wither.The corresponding leaf area index and Leaf SPAD value also decreased;(2)By using PROSAIL model,the response of chlorophyll content and leaf area index to canopy spectral reflectance is obtained firstly.For the spectral reflectance of 400nm-680nm in visible light band,the simulated canopy reflectance spectrum of maize shows a trend of increasing first and then decreasing;for the spectral reflectance of simulated chlorophyll content,with the increase of chlorophyll content,the value of spectral reflectance shows a trend of decreasing.In the visible light band,the spectral reflectance of simulated LAI of maize leaves increases first and then decreases,and the spectral reflectance decreases with the increase of LAI;in the 700nm-1300nm band,the spectral reflectance of five simulated maize leaves decreases with the increase of LAI,which shows that there is a negative correlation between them;(3)Through the local and global sensitivity analysis,it is found that the contribution degree of different parameters to the spectral reflectance is different:in the band of600nm-750nm,the contribution degree of corn chlorophyll content is the largest,and the average sensitivity is about 80%;the contribution degree of equivalent water thickness EWT and dry matter content LMA in the band of 600nm-700nm to the spectral reflectance is the smallest,and the sensitivity is the lowest;in the band of700nm-1300nm,the contribution degree of maize is the lowest.The LAI plays an important role in the contribution of spectral reflectance of maize,and the sensitivity of LAI in this band is the highest,between 80%and 90%.It can be seen that chlorophyll content is the most sensitive to spectral reflectance in visible band,and leaf area index is the most sensitive to spectral reflectance in 700nm-1300nm band;(4)Through the comparison and analysis of the simulated and measured spectra,the single factor regression equation is used to fit the model.Through the model correction of the canopy spectrum,the error of the polynomial function correction is relatively low in the 400nm-700nm band,the R~2 of the fitting equation is 0.917,and the error after the model correction is about 14%,compared with the error before the correction of 36%,the error is reduced by 22%,and the correction effect is reduced In the 700nm-1300nm band,the error of polynomial function correction is relatively low,the R~2 of fitting equation is 0.94,the error of model correction after removing the abnormal value is about 23%,compared with the error before correction of 47%,the error is reduced by24%,and the correction effect is relatively ideal.Therefore,no matter in jointing stage,tassel stage,milk maturity stage or maturity stage,the R~2 of polynomial function fitting equation is the largest,and the effect of correction error is the best;(5)The reflectance spectrum and the look-up table are mapped by the constructed cost function,and then the leaf area index and the chlorophyll content to be retrieved are found out;the linear regression is carried out by using the measured leaf area index and the chlorophyll content value in four growth periods,and the leaf area index regression equation and the chlorophyll content regression equation are obtained,and the fitting effect of the two parameters in four growth periods is obtained The results show that the R~2 of the linear equation constructed by LAI is about 0.7,while the R~2 of the fitting equation constructed by chlorophyll content is more than 0.75 in three periods,which proves the effectiveness of the look-up table method.