雾的前向散射对距离选通成像系统的影响

Effects of forward-scattering of fog on range-gated imaging system

根据辐射传输和Mie散射理论,给出了分析雾的前向散射对距离选通成像系统影响的计算方法。首先,采用雾的含水量和能见度的经验公式估计雾滴谱。其次,已知雾滴谱计算Mie散射相函数;进而获得视消光系数。最后,给出了考虑前向散射光的影响时,前向散射光、后向散射光和信号光在距离选通成像系统光电阴极面上的照度随时间的变化规律,以及光电阴极面上目标与背景图像的对比度。结果是目标上的照度、后向散射光和信号光在光电阴极面上的照度增加,目标与背景图像的对比度降低;前向散射光在光电阴极面上的照度远小于后向散射光。

Based on the radiative transfer and Mie scattering theory, the computing method of analyzing the effects of forward scattering of fog on range-gated imaging system is given. Firstly, the empirical relation of water content and visibility for fog is used to estimate fog drop size distribution. Secondly, the Mie scattering phase function is presented. And then the apparent extinction coefficient can be calculated. Finally, the forward scattering, backscattering and signal irradiance on photo-cathode varying with time and the image contrast between object and background are obtained when the effects of forward scattering are considered. The results demonstrate that the irradiance on object, backscattering and signal irradiance on photo-cathode are increased and the image contrast between object and background is decreased. During the gated time, the irradiance of forward scattering on photo-cathode is much less than backward scattering.