不同病虫害危害程度下云南松针叶光谱模拟及其生化参数敏感性分析

Simulation of Needle Reflectance Spectrum and Sensitivity Analysis of Biochemical Parameters of Pinus Yunnanensis in Different Healthy Status

明确植被叶片反射率对生化参数敏感程度是遥感定量反演生化参数含量的前提。本文以不同健康状态下的云南松针叶光谱为例,基于查找表法(LUT)对针叶光谱模型LIBERTY的叶绿素和水分吸收系数进行了标定。提出了一种新的光谱合成方法和枯黄指数YI,解决LIBERTY模型不能有效拟合严重受害程度的云南松针叶反射光谱曲线的问题。并应用EFAST全局敏感性分析方法,利用标定后的LIBERTY模型定量分析了不同受害程度的针叶生化参数敏感性变化。结果表明:(1)标定后的LIBERTY模型能有效拟合健康针叶光谱(R^2=0.999,RMSE<0.01)、轻度(R^2=0.991,RMSE<0.02)和中度受害针叶光谱(R^2=0.992,RMSE<0.03);但是严重受害针叶光谱模拟能力很差(R^2=0.803,RMSE>0.1)。(2)新光谱合成方法能有效拟合严重受害光谱(R^2=0.991,RMSE<0.03);枯黄指数(YI)能够定量分析受害程度。(3)随着受害程度加深,针叶反射率对叶绿素、水分参数敏感度降低,而基吸收、白化吸收等参数敏感度增大,且存在敏感波段。如在505~565和705~850 nm范围白化吸收对针叶反射率作用明显;对于严重受害针叶,除了叶绿素之外白化吸收对可见光区针叶反射率影响也非常显著;通过引入白化吸收先验知识,发现如果能进一步确定白化吸收情况,能够提高严重受害针叶叶绿素反演的精度。

The sensitivity of biochemical effects on leaf reflectance is vital for retieving biochemical parameters with remote sensing.In this study,the chlorophyll and water absorption coefficients of the commonly used model LIBERTY（leaf incorporation biochemistry exhibiting reflectance and transmittance yields） were calibrated using field measured needle spectral reflectance curves based on a look up table（LUT） method.A novel spectra reflectance fitting method were presented by involving a new index（named as yellow index,YI）,which could obviously improve the fitting accuracy of Pinus yunnanensis reflection spectrum at highly-stressed status.As a global sensitivity analysis method,the EFAST（extended Fourier amplitued sensitivity test） was implemented to quantitatively assess the sensitivity of biochemical parameters on needle reflectance.Results show that：（1） the reflectauce spectrum of healthy needles（R^2 =0.999,RMSE〈0.01）,slightly stressed needles（R^2 =0.991,RMSE〈0.02） and moderately stressed needles（R^2 =0.992,RMSE〈0.03） are simulated fairly well by calibrated LIBERTY model which has less potential in fitting the reflectance spectrum of seriously stressed needles（R^2 =0.803,RMSE〈0.1）.（2） the reflectance spectrum of seriously stressed needles can be successfully simulated by our proposed spectrum reflectance fitting method（R^2 =0.991,RMSE〈0.03）,because YI can quantitatively describe different degrees of stress,and（3） the sensitivity of leaf reflectance to chlorophyll and water parameters decreases with the degree of stress;while the sensitivity to other biochemical parameters is increasing,which includ baseline absorption,albino absorption,Lignin and Cellulose content,and nitrogen content,increases with the stress degree.Needle reflectance spectrum also have sensitivive bands for these parameters.For example,the albino absorption have a significant effect on needle reflectance in 505～565 and 705～850 nm）.In addition,Albino absorption and chlorophyll also have significant effects on needle reflectance in visible region for seriously stressed needles,which indicates that the prior knowledge of the albino absorption level can help obtain the valid inversion result of chlorophyll content.