利用可见光/近红外反射光谱估算土壤总氮含量的实验研究

Experimental Study on Total Nitrogen Concentration in Soil by VNIR Reflectance Spectrum

利用土壤的室内反射率光谱,探讨土壤氮元素的高光谱机理。利用土壤光谱各吸收带的特征参数与总氮含量进行逐步回归运算,确定与氮元素关系比较密切的几个吸收带。计算出这几个特征吸收带内土壤反射率的变化形式:一阶导数(FDR)、倒数(1/R)、倒数之对数(log(1/R))、波段深度(Depth),并与总氮含量进行逐步回归分析,得到比较理想的结果:建模样本的Ra2(修正的判定系数)分别为0 789、0 753、0 736、0 699,验证样本的Ra2分别为0 759、0 468、0 794、0 725。可见土壤的反射率光谱与氮元素含量之间存在比较明显的相关性,可见光/近红外反射光谱具有快速估算土壤中氮元素含量的潜力。

In this paper,the experimental study on extracting total nitrogen in soil by VNIR (visible-near infrared) spectrum is introduced.First,the relationships between absorption features and nitrogen concentration to select the absorption features significantly correlated with nitrogen are analyzed.Then several parameters of spectra in the selected absorption features are calculated,including inverse spectra (1/R),first derivative reflectance spectra (FDR),inverse-log spectra (log (1/R)) and Depth.Using stepwise multiple regression method,the authors establish the statistical relationships between these parameters and nitrogen concentration.The results show good prediction performance: R^2a for model samples are 0.789,0.736,0.753 and 0.699 respectively,and R^2a for test samples are 0.759,0.794,0.468 and 0.725 respectively.The study indicates that soil spectrum in the VNIR range has the potential for the rapid simultaneous prediction of nitrogen concentration.