The Extinction Characters Of Fog At Near And Middle Infrared

Fog has great effect on the capability of military infrared device and on the safety and efficiency of civil traffic.This paper focused on theoretical modeling of extinction characters of fog at near and middle infrared .Accord ing to the model,Compared with experimental data,the correctness and efficiency of numerical simulation was proved.Firstly, the mathematical model of radiation extinction of fog drop was developed.The matlab programs which calculate extinction efficiency of drop based on Mie theory was built,and combined with the refractive index of haze particle, extinction efficiency of three fog drop model were calculated.The calculated results show that:the extinction characters of fog drop was different either to wet haze particle or to water droplet.Only when the inner, outer sphere radius ratio below to 0.4 can fog drop be considered as water drop.Secondly, experimental results of special fog were synthetically analyzed,the size distribution function of fog drop was fitted to these experimental results. The extinction coefficient and visibility of special fog were calculated based on fog drop size distribution. The calculated results were in agreement with the experimental data.Finally,the transmittances of fog at seven selected wavelengths were calculated based on Beerjambert Law.The results show thatithe wavelength of 11.6pm has bigger transmittance than other wavelengths.The extinction characters of rain at near and middle infrared were also studied.These results can give a reference to correlative work.