差分吸收光谱中光源的光谱结构去除研究

差分吸收光谱技术(differential optical absorption spectroscopy,DOAS)利用气体分子在紫外-可见光谱范围的特征吸收来测量其浓度含量,现已被广泛应用于测量大气环境中痕量污染气体的浓度,如SO2,NO2,O3,HCHO等。测量得到的大气差分吸收谱在测量波段内(300～700nm)由于存有光源(氙灯或者氘灯)光谱结构,会影响大气环境中痕量气体浓度的准确反演;在光谱数据反演时,为了避开光源光谱结构的影响,国内外对其处理通常采用分段方式反演和弥补方式反演并介绍一种新的数据处理方法:采用平移窗口均值平滑方法(moving-window average smoothing method)获得大气光谱的慢变化,然后求取氙灯光谱结构。并将获得光源光谱结构对实际测量光谱进行拟合分析,取得了较好的效果,残差为2.995×10-4,避免了选择波段过窄和对新物质探测不利的缺点。

Study on removing the lamp spectrum structure in differential optical absorption spectroscopy

Differential optical absorption spectroscopy (DOAS) technique has been used to measure trace gases in the atmosphere by their strongly structured absorption of radiation in the UV and visible spectral range, and nowadays this technique has been widely utilized to measure trace polluted gases in the atmosphere e.g. SO2, NO2, O3, HCHO, etc. However, there exists lamp (xenon lamp or deuteriumlamp) spectrum structure in the measured band (300-700 nm) of the absorption spectra of atmosphere, which badly impacts on precision of retrieving the concentration of trace gases in the atmosphere. People home and abroad generally employ two ways to handle this problem, one is segmenting band retrieving method, another is remedial retrieving method. In the present paper, a new retrieving method to deal with this trouble is introduced. The authors used moving-window average smoothing method to obtain the slow part of the absorption spectra of atmosphere, then achieved the lamp (xenon lamp in the paper) spectrum structure in the measured band of the absorption spectra of atmosphere. The authors analyzed and retrieved the measured spectrum of the atmosphere, and the result is better than the forenamed ways. Chi-square of residuum is 2.995 x 10(-4), and this method was proved to be able to avoid shortcoming of choosing narrowband and disadvantage of discovering the new component of atmosphere in retrieving the concentration of air pollutants and measuring the air pollutants.