A Brief description of how electromagnetic radiation is useful in Remote Sensing

1. DEVASHISH NEGI AMIT KUMAR
160517 160510
G.B.P.I.E.T
PAURI, GARHWAL
Electromagnetic Radiation
and its use in Remote Sensing
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2. UNDERSTANDING ELECTROMAGNETIC
RADIATION
• Time-varying wave that has both electrical and magnetic components
• is radiated by atomic particles at the source
• propagates through the vacuum of space at the speed of light
• interacts with the Earth's atmosphere
• interacts with the Earth's surface
• finally reaches the remote sensors where it interacts with various
optical systems and detectors
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4. SPECTRAL REFLECTANCE PROPERTIES
• EMR reflected, depends on the nature of the materials and
which portion of the EMR is being measured
• The nature of this reflected component over a range of
wavelengths is called spectral response patterns
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6. SPECTRAL SIGNATURE
• Every natural and artificial object reflects and emits EMR over a range
of wavelengths in its own chemical composition and physical state
• The distinctive reflectance and emission properties of objects are
called spectral signature
• Within some limited wavelength region, a particular object will
usually exhibit a diagnostic spectral response patterns that differs
from other objects
• each material on the earth would have a distinctive spectral response
pattern
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7. SPECTRAL SIGNATURE
• The atmosphere essentially “closes
down” in certain portions of the
spectrum while “atmospheric
windows” exist in other regions that
transmit incident energy effectively
to the ground
• It is within these windows that
remote sensing systems must
function
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8. ATMOSPHERIC WINDOWS
• relatively transparent wavelength regions of the atmosphere
• wavelengths at which EMR are partially or wholly transmitted
through the atmosphere
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9. ELECTROMAGNETIC SPECTRUM
• total range of wavelengths is commonly referred to as the electromagnetic
spectrum
• Any matter with a body temperature greater than 0 K emits electromagnetic
energy. Therefore, it has a spectrum
• different chemical elements have different spectra, they absorb and reflect
spectral energy differently
• Each compound has a unique spectrum due to its unique molecular
structure
• This discriminate one matter from the other
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11. INTERACTION OF EMR WITH ATMOSPHERE
• EMR interacts with particles and gases in the atmosphere
• It can happen in 3 ways
1.Scattering
2.Absorption
3.Refraction
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12. SCATTERING
• occurs when particles or large gas molecules present in the
atmosphere interact with and cause the electromagnetic
radiation to be redirected from its original path
• Depends upon
-Wavelength of the radiation
-Abundance of particles or gases
-Distance the radiation travels through the atmosphere
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13. TYPES OF SCATTERING
• Rayleigh (or molecular) Scattering
• Mie (or non-molecular) Scattering
• Nonselective scattering
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14. RAYLEIGH (OR MOLECULAR OR SMALL
PARTICLE) SCATTERING
• caused by oxygen and nitrogen molecules
• most influential at altitude above 4.5 km
• The amount of Rayleigh scattering is 1/(L)^4, L=wavelength
• As the result, invisible ultraviolet radiation is greatly affected by
Rayleigh scattering
• This explains why the clear sky appears blue
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15. MIE (OR NONMOLECULAR OR LARGE
PARTICLE) SCATTERING
• Occurs when there are sufficient particles in the atmosphere that
have mean diameters from 0.1 to 10 times larger than the
wavelength under consideration
• influences longer radiation wavelengths than Rayleigh scattering
• agents include water vapor and tiny particles of smoke, dust, etc.
• Influence in the lower 4.5 km of the atmosphere
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16. NONSELECTIVE SCATTERING
• Happened when the lower atmosphere contains suspended aerosols(dia. 10
times larger than wavelength)
• example - smoke, water vapor, water droplets, ice crystals in the clouds
and fog
• impacts on almost all spectral bands
• water droplets and ice crystals scatter all wavelengths equally well so that
the clouds in the sunlit sky looks white
• large smog particles cause the color of sky to grey
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17. REMOTE SENSING
• science of acquiring information
about the objects of interest,
without actually being in contact
with it
• is done by sensing and recording
reflected or emitted energy and
processing, analyzing and applying
that information
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18. USING EMR IN REMOTE SENSING
• Remote sensing devices detect EMR reflected from the Earth
surface
• Remote sensing device detect EMR emitted by the Earth itself
• Remote sensing devices generate their own EMR, bounce it off
the Earth’s surface and measure the EMR returned
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19. SPECTRAL REFLECTANCE CURVE
• reflectance characteristics of earth surface feature may be
quantified by measuring the portion of incident energy
(Irradiance) that is reflected (Radiance)
• This energy is measured as a function of wavelength and is
called spectral reflectance
• A graph of spectral reflectance as a function of wavelength is
termed as spectral reflectance curve
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20. SPECTRAL REFLECTANCE EXAMPLES
• Bare soil :
The surface reflectance from
bare soil depends on many
factors such as color,
moisture content, presence
of carbonate and iron oxide
content
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21. SPECTRAL REFLECTANCE EXAMPLES
• Water:
• Longer wavelength visible and near infrared radiation is
absorbed more by water than shorter visible wavelengths
• Water typically looks blue or blue-green due to stronger
reflectance at these shorter wavelengths, and darker if viewed
at red or near infrared wavelengths
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22. SPECTRAL REFLECTANCE EXAMPLES
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