Radio propagation is the behavior of radio waves when they are
transmitted, or propagated from one point on the Earth to
another, or into various parts of the atmosphere. As a form of
electromagnetic radiation, like light waves, radio waves are
affected by the phenomena of reflection, refraction,
diffraction, absorption, polarization and scattering. Radio
propagation is affected by the daily changes of water vapor in
the troposphere and ionization in the upper atmosphere, due to
the Sun. Understanding the effects of varying conditions on
radio propagation has many practical applications, from choosing
frequencies for international shortwave broadcasters, to
designing reliable mobile telephone systems, to radio
navigation, to operation of radar systems. Radio propagation is
also affected by several other factors determined by its path
from point to point. This path can be a direct line of sight
path or an over-the-horizon path aided by refraction in the
ionosphere, which is a region between approximately 60 an