Saturday, October 27, 2012

Radiation- Object interaction

 i have shifted my language to english as i have thought it would be convenient to relate the story in the language it was created.Ok what did i mean by the certain topic above...?

an interaction of the radiation and the object that is being observed occurs when the radiation hits the particular object (lets say "target"),thus there are three forms of interaction taking place when energy,of the radiation, strikes the object,they are;

  1. absorption
  2. transmission
  3. reflection
by '1' we say that the incident energy (පතන ශක්තිය ) is absorbed into the target,(we cannot trace the rays after that incident)

by '2' we say that the incident ray of energy passes through the target 

by '3' we say that the radiation has been bounced back off the target in a direction opposite to the way of its initial propagation    

in remote sensing we are always interested in the number 3 category because that is what we usually let us get an understanding about the reflection phenomena.
Reflection can be divided into two different categories as,
  • specular reflection-where the reflection occurs due to the incident of radiation with a smooth surface,in this particular occasion almost all the energy gets reflected in single direction 
  • diffuse reflection-here the smoothness of the surface is pretty low and hence the energy is reflected almost uniformly in all possible directions      
as mentioned above the type of reflection depends on the surface roughness of the object in comparison to the wavelength of the incoming radiation.we can get it like this,
"if the incoming radiation has got shorter wavelengths than the surface variations the type of reflection would be Diffuse and Specular if it's otherwise "

ok, with that in mind lets move into the more interesting topics, we already know that the reflection occurs in almost every object(let us not be so advanced to talk about the black body radiation at this moment)
and the fact about this reflection is that it is unique to each object.thus we can identify the object using its reflection.

for an example;

tree leaves,absorbs radiation in the wavelength region in red and blue but reflects green,so we see most of the leaves as green in colour.trees would appear extremely bright
to us at these wavelengths. In fact, measuring and monitoring the near-IR reflectance is one
way that scientists can determine how healthy (or unhealthy) vegetation may be.

similarly water absorbs longer wavelengths in visible and near Infrared region but reflects more shorter wavelengths making it "blue" or "blue-green" to our naked eyes.

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