Review Article
Visible and Near-Infrared Reflectance Spectroscopy for Investigating Soil Mineralogy: A Review
Table 2
A review of VNIR spectroscopy for the prediction of soil attributes using feature-based and chemometric methods in previous studies.
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aSoil attributes: clayT, total clay content; clay2:1,2:1 clay mineral content; ClayK, kaolinite content; ClayI, illite content; ClayS, smectite content; FeT, total iron content; FeH, hematite content; FeG, goethite content; C, carbonate content. bsoil type: soil type is not given in the study (not mentioned); the soil samples in the study include more than three soil types (diverse). csample treatment: oven-dried, sieved (<2 mm), and measured under laboratory conditions (lab/sieved (2)-oven-dried); oven-dried, sieved (<0.2 mm), and measured under laboratory conditions (lab/sieved (0.2)-oven-dried); air-dried, sieved (<2 mm), and measured under laboratory conditions (lab/sieved (2)-air-dried); fresh (wet and unprocessed) and measured under field conditions (field/fresh). dncal/nval shows the number of samples used in the spectral calibration and validation, respectively. CV indicates that the validation was conducted independently using a statistical cross-validation technique. epartial least squares regression (PLSR); multivariate adaptive regression splines (MARS); support vector regression (SVR); the discrete wavelet transform-artificial neural networks (DWT-ANN); continuum removal (CR); feature-based multiple linear regression (CR-MLR). fcoefficient of determination. groot mean-square error (g·kg−1). —, RMSE is not given in the study. hmg·kg−1. |