Abstract
Theoretical approach to the problem on the visibility through aerosols has been pursued on following models.
Incident light is a parallel beam coming from backwards to the observer. The objective is a white infinitely long disk with a completely flat clean surface. Visibility is defined to be lost when the intensity of the sum of the total scattered light from aerosol particles to the human eye is balanced to the intensity of reflected light from the objective.
The particle size of aerosols are assumed to be relatively small to the wave-length of the incident light. Hence the Rayleigh and Rayleigh-Gans type scattering has been applied.
Then, visible distance (l) is estimated by the following equation :
∫{NI′J(π-θ)/R2+NI"J(θ)/R2}dυ=ƒI0exp(-2τl)
I′=I0exp(-τz), I"=I0exp(-τ（2ｌ-z))
dυ=2πz2tan θ sec2 θ dθ dz
The most important factor which affects the visible distance has been found to be the shape of the size-distribution of the aerosol particles. The visible distance through fog particles with Size-distribution is 1/10～1/100 times to the one in the case of uniform particle size.
The effect of wave length distribution of the incident light on the visible distance has been estimated shorten the distance ca. 1/10 times to the one in the case of monochromatized light.
Investigation are presently being on the Mie-type scattering case.
