“…The pre-processing method can amplify the original hidden signal differences in the spectral data. Meanwhile, spectral pre-processing techniques can achieve the purpose of improving the resolution of THz spectral data, making the identification more accurate and reliable ( Ndlovu et al, 2021 ; Tafintseva et al, 2021 ). In this paper, seven pre-processing methods were used, including: mean-centering, auto scaling, standard normal variate (SNV), minimum and maximum values to [0 1], multiplicative scatter correction (MSC), first derivative, and second derivative ( Lu, 2006 ; Chu, 2011 ).…”