前向散射能见度仪测量误差的理论分析

前向散射能见度仪(FSVM)是测量能见度的主要仪器.从测量原理和散射理论出发,推导出了FSVM的探测方程,以此为基础,采用模拟计算与统计分析相结合的方法,分析了由于气溶胶性质不确定性和仪器光电机技术性能变化两方面引起的FSVM的8类误差源及其不确定度值.结果及分析表明:现有技术条件下仅考虑光电机性能不确定性而引起的能见度相对不确定度为4%;气溶胶性质不同而引起的相函数变化以及忽略吸收效应是FSVM的主要误差源,考虑到气溶胶性质的不确定性,能见度相对不确定度可达28%;若能识别出气溶胶性质,对于单一的雾、乡村型气溶胶和城市型气溶胶,能见度相对不确定度分别为7%、9%和18%;相函数对散射角的变化比较敏感,由于运输、架设和使用过程会对散射角产生相当的影响,必须对散射角进行校准.研究结果对FSVM的使用、改进和校准提供了理论支持.

Theoretical analysis on measurement error of forward scattering visibility meter

Forward scattering visibility meter (FSVM) is the main instrument to measure the visibility. The detection equation of FSVM was deduced based on the measuring principle and scattering theory. The error sources of FSVM and their uncertainty, which were caused by uncertainty of aerosol properties and performance change of optical electronic instrument, were analyzed by simulation calculation and statistical methods. The results show that the relative uncertainty of visibility caused by performance uncertainty is only 4% under the current technological conditions. The main error sources of FSVM are scattering phase function changes caused by aerosol properties and neglectable absorption effect. Because of uncertainty of aerosol properties,the relative uncertainty of FSVM reaches 28% actually. When the atmospheric aerosols are classified to fog,rural aerosol and urban aerosol,the relative uncertainties are 7%, 9% and 18% respectively under some specific conditions. The scattering phase function is sensitive to the change of scattering angle. The calibration of the scattering angle is necessary as the scattering angle changes in some cases such as transportion, erection and exploitation.The results can provide important theoretical support for the use, improvement and calibration of FSVM.