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基于光纤收发一体的差分吸收光谱空气监测系统研究
Research on a New Doas System with Combined Transmitting-receiving Fibers for Air Quality Monitoring
【作者】 梁玉洁；
【导师】 徐可欣；
【作者基本信息】 天津大学 ， 生物医学工程， 2010， 硕士
【摘要】 随着工业和交通运输业的迅速发展,城市空气污染日趋严重,直接并严重影响着生态平衡和人类健康,因此大气污染成分的监测和控制具有相当重要的意义。为了实现对空气质量的连续监测,本文根据差分吸收光谱法(Differential Optical Absorption Spectroscopy,DOAS)检测痕量气体的基本原理,研制了基于光纤收发一体的差分吸收光谱空气质量监测系统,并采用设计的样机进行了标准气体和现场空气测量。本文主要内容如下:1、首次提出了基于光纤收发一体的差分吸收光谱测量系统,用于空气质量监测。与目前传统DOAS系统相比,简化了测量结构,提高了检测性能。2、实现和改进了差分光谱的分离算法。提出改进的光谱分离公式,利用测量光谱低频成分与其相比较的方法得到差分吸收光谱,可避免光源能量不稳定的影响;分析比较了多项式拟合、傅里叶变换及Savitzky-Golay平滑滤波三种方法对光谱低频成分的提取效果,采用Savitzky-Golay平滑滤波技术完成光谱分离,改善了对光谱低频成分的拟合程度。3、提出了分波段的浓度反演方法,在划分的波段范围内分别利用最小二乘法进行气体浓度反演,取目标气体在其主要吸收波段内的反演结果作为该气体的测量浓度,进一步提高了反演的准确度。4、完成了基于光纤收发一体的差分吸收空气质量监测系统设计,并采用所开发的样机实现了标准气体和空气中痕量气体的测量。
【Abstract】 With the development of industry and transportation, air pollution becomes worse every day, seriously affecting ecological balance and human health, so it is significant to monitor and control the atmospheric pollution. In order to monitor the air quality continuously, a system with combined transmitting-receiving fibers was developed, on the base of Differential Optical Absorption Spectroscopy (short as DOAS).The main content of this paper is listed as follows:Firstly, a new design of the DOAS measurement system with combined transmitting-receiving fibers was proposed for the first time. Compared with the tradition DOAS system, the new one can simplify the measurement structure and improve the detection performance.Secondly, the separation algorithm of differential spectrum was implementation and improved. An improved separation formula was put forward to obtain the differential optical absorption spectrum, and the basic idea was comparing the original spectrum with its low-frequency component, which could avoid the instability of the energy source. Three methods: polynomial fitting, Fourier transformation and Savitzky-Golay smoothing filter, for low-frequency component extracting were analyzed and compared, and the results showed that Savitzky-Golay smoothing filter technique had the best effect on the fitting of low-frequency component.Thirdly, a novel calculation method with sub-band was put forward to improve the retrieval accuracy, whose basic idea was calculating the gas concentrations within the division bands by the method of least square, and then taking the result at every gas’s main absorption band as its final measurement concentration.Finally, the new DOAS air monitoring system with combined transmitting- receiving fibers was produced to measure the standard gases and the air quality.