一阶导数、二阶导数，矢量归一化（SNV），多元散射校正（MSC），数据中心化，直接信号校正，平滑处理六种光谱数据预处理的方法-A first derivative, second derivative, vector normalization (SNV), multiplicative scatter correction (MSC), the data center of the direct signal correction, smoothing six kinds of spectral data preprocessing methods