Calibration and validation statistics of partial least-squares regression models.

Calibrations were evaluated as follows (Saeys et al (2005): excellent (R2/r2 ≥ 0.9, RPD ≥ 3.0), reliable quantitative predictions (R2/r2 ≥ 0.75 and 2/r2 ≥ 0.65 and 2/r2 Transf: transformations for regression analyses.Abs: Log1/R (R = reflectance).1D: first derivative.R2: coefficient of multiple determination (calibration).SEC: standard error of calibration.SECV: standard error of cross validation.r2: regression coefficient NIRS predicted vs. observed values.SEP: standard error of prediction (validation).RPD: ratio of SD of reference values (validation) to SEP.RPIQ: ratio of the interquartile distance IQ ( = Q3–Q1) of reference values (validation) to SEP.Corr. OM: Pearson correlation with organic matter content.校准模型的评估标准如下（参考Saeys等（2005）的研究成果）： 优秀等级判定：多重决定系数（R2/r2, coefficient of multiple determination）≥0.9，且相对分析误差（RPD, ratio of SD of reference values to SEP）≥3.0； 可靠定量预测等级判定：R2/r2 ≥ 0.75 且 2/r2 ≥ 0.65 且 2/r2； Transf：用于回归分析的变换（transformations for regression analyses）； Abs：以1/R的对数值表示（Abs: Log1/R，其中R为反射率（reflectance））； 1D：一阶导数（first derivative）； R2：校准多重决定系数（coefficient of multiple determination, calibration）； SEC：校准标准误（standard error of calibration）； SECV：交叉验证标准误（standard error of cross validation）； r2：近红外光谱（NIRS, Near-Infrared Spectroscopy）预测值与实测值的回归系数（regression coefficient between NIRS predicted and observed values）； SEP：预测（验证）标准误（standard error of prediction (validation)）； RPD：验证集参考值的标准差（SD, standard deviation）与SEP的比值（ratio of SD of reference values (validation) to SEP）； RPIQ：验证集参考值的四分位距（IQ, interquartile distance = Q3–Q1）与SEP的比值（ratio of the interquartile distance IQ ( = Q3–Q1) of reference values (validation) to SEP）； Corr. OM：与有机质含量的皮尔逊相关系数（Pearson correlation with organic matter content）。