提出了基于经验模态分解(EMD)的多次去噪方法来降低多光程吸收光谱中的干涉噪声。从理论上分析并确定了降噪的次数,对采用直接吸收和波长调制二次谐波光谱技术探测得到的不同体积分数的CO₂谱线进行了多次EMD降噪处理,并与多次平均和低通滤波的降噪方法进行了对比。结果表明:多次EMD去噪能更有效地滤除光谱信号中的干涉噪声和随机噪声,且降噪后的信号幅值与待测气体的体积分数满足较好的线性关系,系统的探测灵敏度能达到3.5×10 ^-5。测量了不同压强和温度下CO₂标准气体的光谱信号,经多次EMD去噪处理后的光谱信号,其干涉的幅值相对于去噪前减小了近两个量级,信噪比增大了约两个量级。

A multi-denoising method based on the empirical mode decomposition (EMD) is proposed to minimize the interference noises in the multi-pass absorption spectra. The denoising number is theoretically analyzed and determined. The CO2 spectral lines with different volume fractions detected by the direct absorption technology and wavelength modulation spectroscopy at second harmonic are denoised by the multi-EMD, and the results are compared with those by the denoising methods with multi-averaging and low-pass filtering. The results show that the interference and random noises can be effectively filtered by the multi-EMD denoising method. Moreover, the denoised signal amplitude has a good linear relationship with the volume fraction of the gas to detect, and the detection sensitivity of the whole system is up to 3.5 × 1 0-5. The spectral signals of CO2 standard gas at different pressures and temperatures are detected. After the multi-EMD denoising, the interference amplitudes of the spectral signals are reduced by about two orders of magnitude, but the signal to noise ratios are enhanced by about two orders of magnitude.