基于TDLAS技术与小波变换去噪算法的甲烷浓度检测

为进一步提高甲烷浓度检测精度，搭建了基于TDLAS（tunable diode laser absorption spectroscopy）技术的甲烷浓度检测实验系统，利用甲烷在波长1653.72 nm处吸收强度很高且可以最大限度消除其他气体干扰的特性，通过提取二次谐波信号实现甲烷浓度检测。然后分别采用heursure硬阈值算法、heursure软阈值算法和sqtwolog固定阈值算法作为小波变换阈值算法，通过分析未去噪及小波变换去噪处理后得到的甲烷吸收信号谱图、甲烷二次谐波信号谱图、甲烷吸收信号的信噪比和均方根误差，优选sqtwolog固定阈值算法作为小波变换阈值算法。不同浓度的甲烷标气线性拟合实验及特定浓度的甲烷标气重复性实验结果表明:通过小波变换（采用sqtwolog固定阈值算法）能有效降低噪声干扰，去噪处理后提取的二次谐波信号与甲烷真实浓度拟合优度R2为0.984，拟合效果更佳。采用TDLAS技术结合小波变换去噪算法，实现甲烷浓度检测的同时也能提高甲烷浓度检测精度。

Detection of Methane Concentration Based on TDLAS Technology and Wavelet Transform Denoising Algorithm

To improve the detection accuracy of methane concentration, an experimental system based on tunable diode laser absorption spectroscopy(TDLAS) technology was built. Taking advantage of the high absorption intensity of methane at a wavelength of 1653.72 nm and its ability to eliminate the interference of other gases to the greatest extent, methane concentration was detected by extracting the second harmonic signal. The heursure hard threshold algorithm, heursure soft threshold algorithm, and sqtwolog fixed threshold algorithm are used as the wavelet transform threshold algorithms, respectively; the sqtwolog fixed threshold algorithm is preferred as the wavelet transform threshold algorithm by analyzing the methane absorption signal spectrum, the methane second harmonic signal spectrum, the signal-to-noise ratio and root mean square error of the methane absorption signal obtained without denoising and after denoising. The results of the linear fitting experiment of methane standard gas with different concentrations and the repeatability experiment of methane standard gas of a specific concentration show that the noise interference can be effectively reduced by the wavelet transform using the sqtwolog fixed threshold algorithm. The goodness of fit R2 between the second-harmonic signal extracted after denoising and the real methane concentration was 0.984, indicating that the fitting effect was better. TDLAS technology combined with the wavelet transform denoising algorithm can realize the detection of methane concentration and improve the detection accuracy of methane concentration. TDLAS technology combined with the wavelet transform denoising algorithm can realize the detection of methane concentration and improve its detection accuracy.