绿洲城市土壤砷含量高光谱估算
Hyperspectral inversion of arsenic content in soil in an oasis city
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摘要: 砷(As)是具有强致癌性的类金属元素, 快速、准确地监测土壤中As元素含量尤为重要。首先, 以乌鲁木齐市表层土壤为研究对象, 采集84组土壤样品, 并测定其As含量和原始光谱反射率, 用Pearson相关分析对土壤原始光谱及12种光谱变换下的光谱反射率与土壤As含量之间的关系进行检验, 筛选出特征波段; 然后, 基于偏最小二乘回归(partial least squares regression, PLSR)、随机森林回归(random forest regression, RFR)以及支持向量机回归(support vector machine regression, SVMR), 构建As含量高光谱反演模型; 最后, 选取决定系数R2、均方根误差(root mean square error, RMSE)和平均绝对误差(mean absolute error, MAE)来评估高光谱模型的反演预测能力。结果表明: 对原始光谱数据进行微分变换能够有效增强光谱特征, 提高土壤光谱反射率与As含量之间的相关性。3种模型的反演预测能力由高到低依次为: RFR> SVMR> PLSR, 其中, 基于均方根二阶微分的RFR模型R2为0.821, RMSE为0.143 mg/kg, MAE为0.523 mg/kg, 模型拟合效果最好, 具有较高的稳定性和预测精度。研究可为构建绿洲城市土壤As含量高光谱反演模型提供科学依据。Abstract: Arsenic (As) is a metalloid element with high carcinogenicity, rendering it particularly important to detect As content in soils in a swift and accurate manner. The study focused on the topsoil in Urumqi City, where 84 soil samples were collected and tested for their As content and original spectral reflectance. This study examined the relationships of As content in the soils with the spectral reflectance under the original spectra and 12 spectral transformations using the Pearson correlation analysis, followed by screening characteristic bands. Hyperspectral models for the inversion of As content in soils were developed using partial least squares regression (PLSR), random forest regression (RFR), and support vector machine regression (SVMR). Finally, the prediction performance of the hyperspectral models was elevated based on the coefficients of determination (R2), root-mean-square errors (RMSEs), and mean absolute errors (MAEs). The results indicated that applying differential transformations to the original spectral data can effectively enhance the spectral features and improve the correlation between spectral reflectance and As content in soils. The prediction performance of the hyperspectral models decreased in the order of RFR, SVMR, and PLSR. The RFR model based on root-mean-square second order differentiation (RMSSD-RFR) exhibited the best fitting effects and the highest prediction stability, with R2 of 0.821, a RMSE of 0.143 mg/kg, and a MAE of 0.523 mg/kg. This study provides a scientific basis for developing hyperspectral models for the inversion of As content in soils in an oasis city.
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