EMR INTERACTION WITH THE ATMOSPHERE
The most important source of electromagnetic radiation
is the sun. Before sun’s energy reaches the surface of
the earth three fundamental interaction in the
atmosphere are possible . These are absorption,
transmission , and scattering .
Electromagnetic energy travelling through the
atmosphere is partly absorbed by various molecules.
The most efficient absorbers of solar radiation in the
atmosphere are ozone(O3),water vapour (H2O),and
carbon dioxide (CO2)
Ozone serves to absorb the most harmful (to most
living things) ultraviolet radiation from the sun.
Some energy are transmitted through the
atmosphere in the wave length from 0 to 22
µm which is called “atmospheric windows”
Without this “atmospheric windows” remote
sensing process is not possible .
Scattering are occurs when particles or large gases
molecules are present in the atmosphere.
Due to the interaction electromagnetic radiation is
redirected from its original path.
How much scattering are takes place depends on
several factors including the wave length of the
radiation, the abundance of particles or gases, and
the distance the radiation travels through the
atmosphere .there are three types of scattering which
take place :– Rayleigh scattering, Mie scattering, and
Non selective scattering .
This scattering occurs when particles size are very
small compared to the wavelength of the radiation .
These could be particles such as small specks of
dust or N2 and O2 molecules .
Rayleigh scattering is the dominant scattering
mechanism in the upper atmosphere.
Sky appears blue in colour due to this kind of
Mie scattering occurs when the particles are just
about the same size as the wavelength of the
Dust, Pollen , smoke, water vapour are the common
causes of mie scattering which tends to affect longer
wavelength than rayleigh scattering .
This type of scattering occurs mostly in the lower
portions of the atmosphere where larger particles are
The final scattering is non selective scattering , occurs
when the particles are much larger than the wavelength of
the radiation .
Water droplets and large dust particles can cause this
type of scattering .
Non selective gets its name from the fact that all
wavelength are scattered about equally.
This type of scattering causes fog and clouds to appear to
our eyes because blue , green, and red light are scattered
in approximately equal quantities (Blue + Green + Red =
white light )