二次傅里叶变换去噪在差分吸收光谱技术中的应用研究

Study on the application of double fourier transform denoising in differential absorption spectroscopy

实际烟气测量中,容易受烟气内多种组分和尘以及介质不均匀、瑞利散射、米散射等因素的影响,应用傅里叶变换寻求信号的频率特性,去除噪声等干扰。提出一种新的差分吸收光谱法,将获取的差分吸收光谱进行两次傅里叶变换,一次傅里叶变换去除噪声干扰的影响;二次傅里叶变换利用对应的特征频率幅值与浓度的关系,建立浓度反演方程,由气体差分吸收光谱经两次傅里叶变换后的特征幅值直接求出气体浓度。新的差分吸收光谱法完全摆脱了扣除暗电流的差分吸收光谱技术分析过程,减少了差分吸收光谱分析和气体浓度反演过程,有利于提高浓度反演精度。

In the actual flue gas measurement,it is easy to be affected by varios components in the flue gas,such as the dust and the inhomogeneous media,Rayleigh scattering,Mie scattering. So it is one of the best ways to apply the Fourier transform to find the frequency characteristic of the signal and remove noise and other interference. A new differential optical absorption spectroscopy is proposed,and the obtained differential absorption spectra is subjected to the double Fourier transform. The effect of noise is removed by the first Fourier transform. The second Fourier transform is used to obtain the relationship between the characteristic frequency amplitude and the concentration,and establish concentration inversion equation. Then the gas concentration is calculated directly by the characteristic amplitude of the two Fourier transform. This new method completely eliminates the analysis process of the differential absorption spectroscopy that is used to reduce the dark current,which greatly reduce the difference between the absorption spectrum analysis and the gas concentration inversion process,and which improve the precision of the inversion concentration.