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    基于连续投影算法的土壤全氮和碱解氮含量高光谱估测

    Hyperspectral Estimation of Total Nitrogen and Alkali Hydrolysable Nitrogen Contents in Tobacco Growing Soil Based on Successive Projection Algorithm

    • 摘要: 基于高光谱数据构建土壤全氮和碱解氮含量估测模型,为准确快速检测植烟土壤全氮和碱解氮含量提供新方法。以会东县和会理市植烟土壤为研究对象,利用高光谱成像获取土壤光谱反射率数据,应用连续投影算法(SPA)和相关分析法(CA)筛选特征波段,并分别采用全波段和特征波段构建偏最小二乘回归(PLSR)、岭回归(RR)和核岭回归(KRR)模型来估测土壤全氮和碱解氮含量。结果表明:(1)原始光谱经4种预处理方法处理后,建立的估测模型精度均有提高;其中经一阶导数(D1)组合标准正态分布(SNV)预处理后,使用全波段建立的全氮和碱解氮含量估测模型精度均较高。(2)SPA筛选出了10个土壤全氮特征波段,13个土壤碱解氮特征波段,分别占全波段数量的2.58%和1.98%。(3)原始光谱经D1-SNV预处理后,用SPA筛选特征波段构建的全氮和碱解氮含量KRR估测模型性能均较好;全氮估测模型验证集决定系数(R2)为0.87,均方根误差(RMSEV)为0.23,相对分析误差(RPD)为2.77;碱解氮估测模型验证集的R2为0.91,RMSEV为14.15,RPD为3.39。运用SPA结合KRR构建的模型能较好地估测研究区土壤全氮和碱解氮含量,D1-SNV-SPA-KRR方法可实现该地区全氮和碱解氮含量的准确估测。

       

      Abstract: The estimation model of soil total nitrogen and alkali hydrolysable nitrogen was constructed based on hyperspectral data, which might contribute a new method for accurate and rapid detection of total nitrogen and alkali hydrolysable nitrogen in tobacco growing soil. Soils were sampled from Huidong and Huili, Sichuan Province, and the soil spectral reflectance data were obtained by hyperspectral imaging technique. The successive projection algorithm (SPA) and correlation analysis (CA) were employed to screen feature band, while partial least square regression (PLSR), ridge regression (RR) and kernel ridge regression (KRR) models were constructed to estimate the contents of total nitrogen and alkali-hydrolyzed nitrogen in soil by using whole and feature band, respectively. Results showed as the followings. 1) The accuracy of the estimation model was enhanced after the original spectrum was processed by four preprocessing methods. After the first derivative (D1) combined with the standard normal variate (SNV), the estimation models of total nitrogen and alkali hydrolyzed nitrogen contents established by using whole band exhibited high accuracy. 2) By using SPA, 10 feature bands of soil total nitrogen and 13 feature bands of soil alkali-hydrolyzed nitrogen were screened out, accounting for 2.58% and 1.98% of the total bands, respectively. 3) After the original spectrum was processed by D1-SNV, better performance was found in the KRR estimation model of total nitrogen and alkali hydrolyzed nitrogen content constructed by SPA screening feature bands. The coefficient of determination (R2), root mean square error of validation (RMSEV) and residual prediction deviation (RPD) of the validation set of total nitrogen estimation model were 0.87, 0.23 and 2.77 respectively. The R2, RMSEV and RPD of the validation set of alkali hydrolysable nitrogen estimation model were 0.91, 14.15 and 3.39 respectively. For tobacco growing soils in the research area, the model constructed by SPA and KRR can estimate the total nitrogen and alkali hydrolyzed nitrogen contents, whereas D1-SNV-SPA-KRR method can achieve accurate estimation on the contents of total nitrogen and alkali hydrolyzed nitrogen.

       

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