滤光片对非色散成像系统获取污染气体柱浓度的影响

Influence of Filter on Column density of Polluted Gas in Non-Dispersive Imaging System

研究了滤光片对非色散可见成像系统获取污染气体柱浓度的影响。分析了滤光片的中心波长与入射角度之间的关系,发现滤光片的中心波长随入射角度的增大向短波方向移动,当入射角度为40°时,滤光片的中心波长漂移17.4 nm。探讨了不同滤光片对信噪比(SNR)、线性响应及灵敏性的影响。研究结果表明,可通过延长曝光时间或叠加图片增大SNR;半峰全宽为10 nm的滤光片具有较好的灵敏性;0.9以上的线性响应系数表明,半峰全宽为40 nm的滤光片仍满足非色散成像系统解析污染气体柱浓度的理论条件;半峰全宽为10 nm的滤光片的检测下限最优,约为4.475×10^(16) molecule/cm^2,获取污染气体柱浓度的滤光片最佳半峰全宽取值范围为2～40 nm之间。基于半峰全宽为10 nm、中心波长为450 nm的滤光片对某钢铁厂烟囱的烟羽进行了测量,获得了烟羽中NO_2柱浓度的二维空间分布图。

The effect of filter on the column density of polluted gas in the non-dispersive visible imaging system is studied. The relationship between central wavelength and incident angle is analyzed for the filter, and it is found that the central wavelength of the filter shifts toward the short-wave direction with the increase of the incident angle. When the incident angle reaches up to 40°, the center wavelength of the filter has a drift of 17.4 nm. The influences of different filters on the signal to noise ratio(SNR), linear response and sensitivity are also discussed. The research results show that the SNR can be increased by the increase of exposure time or by the image stack. The filter with a full width at half maximum(FWHM) of 10 nm possesses good sensitivity. At the same time, the linear response coefficient above 0.9 indicates that a filter with a FWHM of 40 nm can still satisfy the theoretical condition for resolving the column density of polluted gas in the non-dispersive imaging system. The detection limit for a filter with a FWHM of 10 nm is the best, which is about 4.475×1016 molecule/cm2. The optimal FWHM is between 2 nm and 40 nm for obtaining the column density of polluted gas. Based on the filter with a FWHM of 10 nm and a central wavelength of 450 nm, the two-dimensional spatial distribution map of NO2 column density is obtained by measuring remotely the smoke plume from the chimneys in one steel plant.