针对近红外透射和吸收双光谱提出一种自适应的去噪方法.同步采集样品的近红外透射谱和吸收谱,在相同分解原则下总体经验模态法分解两组光谱,得到单组分特征模态分量.计算特征模态分量与原透射谱、吸收谱之间相关性,以及两组特征模态分量之间相关性,相关性最小模态分量初判为噪声分量.分析该分量在光谱中点处自相关性,若中点处很大,其他点几乎为零或很小,可以判断该分量为噪声.这种基于模态分量相关性的噪声判别方法称为“3R”法则.剔除噪声分量,重构光谱信号,循环上述分解过程,直到不满足“3R”法则,降噪过程结束.构造理想光谱,叠加噪声,“3R”法降噪效果优于EMD和EEMD低通滤波器,略逊于小波分解.真实光谱实验中,经过上述方法降噪处理过的玉米叶片光谱采用3层BP神经网络建立与叶绿素之间预测模型,“3R”法处理模型具有最大校正相关系数和预测相关系数,最小校正标准差和预测标准差.在四种降噪方法中,“3R”法对光谱谱峰位置和峰高的影响最小.实验表明,“3R”双谱去噪方法无需预设迭代次数,不用考虑分解层数,没有基函数,是自适应的,该方法适合近红外光谱去噪。

Adaptive de-noising algorithm is proposed based on transmission spectrum and absorption spectrum of near infrared.Near infrared transmission spectrum and absorption spectrum collected synchronously are decomposed into intrinsic mode functions by ensemble empirical mode decomposition;the intrinsic mode function is a single frequency component.Correlations between intrinsic mode functions and transmission spectrum,absorption spectrum were calculated,and the correlation between intrinsic mode functions of transmission spectrum and absorption spectrum was also computed.The results show that the intrinsic mode function with minimum correlation coefficient should be noise component.The self-correlation of this intrinsic mode function was analyzed to judge whether the intrinsic mode function is noise.IF the self-correlation is very large at the midpoint and is zero or very small at the other point of the spectrum,then the intrinsic mode function is noise component for judgment,based on which “3R” algorithm is named to judge whether the intrinsic mode function is noise component.Removing noise component,constructing spectral signal and circulating the previous decomposition was conducted,and the noise reduction process was ended until it did not meet the “3R” rule.To do experiment on the simulated spectrum with noise,the effect of de-noising with “3R” algorithm is better than EMD and EEMD low pass filter,and it is not so good as wavelet decomposition.In the real spectrum testing,the model was established between spectra treated by above methods with chlorophyll on three layers.BP neural network,and the model de-noised by “3R” method has the biggest correlation coefficient and prediction coefficient,but the smallest correction standard error and prediction standard error.“3R” method’s effects on the peak position and peak intensity of spectrum are the smallest among the four kinds of de-noising methods.Experiments show that the “3R” algorithm based on bi-spectrum can be used for near infrared spectra de-nosing without presetting the number of iterations,there is no need to consider layers of decomposition,also no need of basis function,and the adaptability is very strong.