Page 12 - RemoteSnsing&GIS by PK Gogoi

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.2.Radiation & Interaction with In the upper atmosphere, above 4.5 km height, scattered more by dust particles,water vapor etc. Without this protective layer in the atmosphere

2Atmosphere(B) : As the energy travels this reyeigh scattering occurs ,and the ‘Blue’ . This leads to high blending of RED colour in our skin would burn when exposed to sunlight.
from its source to the target i.e. on the different c o l o u r the sky in the morning and evening Carbon dioxide referred to as a greenhouse gas.

features of the earth, it will come in contact with with high- ie Scattering : It occurs in lower This is because it tends to absorb radiation
and interact with the atmosphere it passes frequency Matmosphere when particles are just about strongly in the far infrared portion of the

through. The atmosphere scatters, absorbs and and low the same size as spectrum - that area associated with thermal
reflects a portion of this Electromagnetic the wavelength heating - which serves to trap this heat inside the

radiation twice when traveling through the of the Radiation. atmosphere. Water vapor in the atmosphere
atmosphere. In the following paragraphs we will wavelength of EMR is scattered more than the It is caused by absorbs much of the incoming and outgoing

other colours. Blue colour of sky is a result of pollen, dust shortwave infrared and long wave microwave
the Rayleigh scattering. This scattering is particles , smoke radiation (between 22gm and 1m. Moreover,

responsible for ‘Haze’ in imagery. However, and other the rate of absorption differs geographically at
with the help of filter in sensor, such haziness particles in the atmosphere. It is non selective to different period of times e.g . the air mass above

can be minimized. the wavelength. Atmospheric components viz. a desert would have very little water vapor to

hy Colour of the sky appeared ‘BLUE’ dust particles, Water droplets etc have a diameter absorb energy, while the tropics it posses high
discuss about basic idea of the process of Win the day and ‘RED’ in the morning of 5 to 100 um can scatter all visible to IR concentrations of water vapor (i.e. high
Scattering, Absorption ,and Reflection of and evening ? radiation. In this scattering of visible range of humidity). As these gases (cloud) absorb

incoming shortwave solar and outgoing EMR, equally all the colours -blue, green and electromagnetic energy at different rate ,
s in the visible
terrestrial energy with that of atmospheric red - are scattered. This scattering is responsible therefore the response to sensor also differs.
Aportion of the
components viz dust particles,water vapors etc. for white colour of the sky. ot all the wavelengths of EMR can
EMR the blue colour
. Scattering : It means Redirection of EMR has low on Selective Scattering: It occurs when Npenetrate through the atmosphere due to
1from its original path. Scattering is a process wavelength,and in the Nthe particles are much larger than the scattering and absorption

by which "small particles suspended in a day time the traveling wavelength of the radiation and all wavelength by the atmospheric
medium of a different index of refraction diffuse path of the sun light through the atmosphere is are scattered equally in all directions. The water elements. Without

a portion of the incident radiation in all shorter , therefore the low wavelength with droplets, ice fragments and large dust particles reaching the target or
directions". While Scattering, there is no energy ‘Blue’ colour is cause this. the earth surface ,the different wavelengths are

transformation, but a change in the spatial scattered more by bsorption : Absorption is the other main either absorbed ar radiated back to the
distribution(direction) of energy. As far as the small specks of dust or Amechanism when electromagnetic atmosphere.

scattering of electromagnetic energy of solar nitrogen and oxygen radiation interacts with the atmosphere. In
and terrestrial energy by atmospheric particles is molecules . Thus, sky contrast to scattering, this phenomenon causes

concerned, it has three distinct characteristics. looks BLUE in colour molecules in the atmosphere to absorb energy at
These are :- due to Rayleigh scattering . On the contrary, in various wavelengths. Ozone, carbon dioxide,

ayleigh Scattering: Rayleigh scattering the morning and evening , the path of sunlight is and water vapour are the three main atmospheric

Roccurs when the size of the particle more , and shortwave waves are scattered constituents which absorb radiation. Ozone A tmospheric Windows:
responsible for the scattering event is much without entering into the atmosphere . The long serves to absorb the harmful (to most living Parts of the spectrum which are not

smaller than the wavelength of the incident light. wave EMR having orange-red colour is things) ultraviolet radiation from the sun. severely Influenced by atmospheric absorption