EM 1110-2-2907
1 October 2003
(Figure 2-1; path B). The total distance the radiation travels in the atmosphere is called
the path length. For electromagnetic radiation emitted from the Earth, the path length will
be half the path length of the radiation from the sun or an active source.
(1) As radiation passes through the atmosphere, it is greatly affected by the atmos-
pheric particles it encounters (Figure 2-12). This effect is known as atmospheric scatter-
ing and atmospheric absorption and leads to changes in intensity, direction, and wave-
length size. The change the radiation experiences is a function of the atmospheric
conditions, path length, composition of the particle, and the wavelength measurement
relative to the diameter of the particle.
Figure 2-12. Various radiation obstacles and scatter paths. Modified from two sources,
(2) Rayleigh scattering, Mie scattering, and nonselective scattering are three types
of scatter that occur as radiation passes through the atmosphere (Figure 2-12). These
types of scatter lead to the redirection and diffusion of the wavelength in addition to
making the path of the radiation longer.
b. Rayleigh Scattering. Rayleigh scattering dominates when the diameter of atmos-
pheric particles are much smaller than the incoming radiation wavelength (φ<λ). This
leads to a greater amount of short wavelength scatter owing to the small particle size of
or...
Rayleigh Scatter = 1/ λ4
(2-5)
2-15
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