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Basic of Remote Sensing V

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How is Energy Transferred?
The energy can be transferred in the three basic ways: conduction, convection, and radiation.
The transfer of energy by electromagnetic radiation (EMR) is of primary interest to remote sensing because it is the only form of energy transfer that can take place in a vacuum (the region between the Sun and the Earth).
The Sun bathes the Earth’s surface with radiant energy causing the air near the ground to increase in temperature. The less dense air rises, creating convectional currents in the atmosphere.
Energy may be conducted directly from one object to another as when a pan is in direct physical contact with a hot burner.
Energy Interactions
When Electro-Magnetic (EM) energy is incident on any given earth surface feature, three fundamental energy interactions are possible. 
  • Reflection (ER)
  • Absorption (EA)
  • Transmission (ET)
Incident Energy (EI) = reflected energy + transmitted energy + absorbed energy
Three forms of Interaction
I = A + R + T or A/I + R/I + T/I = 1 (100%)
The proportions of energy reflected, absorbed and transmitted will vary for different earth features depending on their material type and condition.
That is even within a given feature type, the proportion of reflected, absorbed and transmitted energy will vary at different wavelengths.
Two features may be distinguishable in one spectral range but not in another wavelength region.
Black-body
An ideal thermal emitter is called a Black-body. (aka Planckian radiator). It is an object that would absorb all radiation incident upon it. A black-body is an ideal surface as:
  • Its emissivity = 1. in other words it radiates the entire energy whatever it absorbed.
  • For a given temperature and wavelength, no body can emit more energy than a black-body.
  • Emission from a black-body is independent of direction, i.e., it is a diffuse emitter.
The radiation that such an idealized object would emit when it is hot is known as Black-body radiation. A black-body is a perfect emitter and absorber of EM radiation.
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