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Latimer [322,323] suggested the approximations based on
a combination of the RDG and AD theories for spheroids and the Mie theory
to describe scattering and extinction of light by non-spherical particles.
The idea of these approximations is as follows:
on the base of the RDG and AD theories to find
an analogy between the formulas for the scattering characteristics
for a sphere and an oriented spheroid. From this analogy
one postulates a certain relationship between the radius and
refractive index of an ``equivalent'' sphere from one side,
and the spheroid parameters (including the orientation) from another side.
Then the scattering by a spheroid or an ensemble of spheroids
is replaced by scattering by the ``equivalent'' sphere calculated from
the Mie theory.
Such approximations are useful as simplified computational algorithms,
though do not have rigorous enough physical justifications.
In certain sense such a method is analogous to a more
pragmatic approach when the exact formulas or results of calculations
are approximated by simple approximate analytic expressions.
For example, such approach was used both for approximation of formulas
of the Mie theory [20,73,128,214,229,247,248,249,492,512]
and for description of scattering by spheroids [218] and
cylinders [437,438,439].
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