Electromagnetic%20Radiation

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Electromagnetic Radiation
Electromagnetic Spectrum Radiation
Laws Atmospheric Absorption Radiation Terminology
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Electromagnetic Radiation
Remote sensing images record the interaction of
electromagnetic energy with the earths surface.
The most familiar form of electromagnetic
radiation is VISIBLE LIGHT.
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Electromagnetic Radiation
Two properties of electromagnetic radiation (1)
wave, and (2) particle.
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Wavelength, Amplitude and Frequency
l is the wavelength c is the speed of light (
3108 m/s) n is the frequency (s-1 Hz)
l c/n
wavelength
Energy levels
Amplitude
lred 3x108/4.6x1014 650 x 10-9 m 650 nm
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Frequencies used in remote sensing
unit Frequency (cycles per second)
Hertz (Hz) 1
Kilohertz 103 (1,000)
Megahertz (MHz) 106 (1,000,000)
Gigahertz (GHz) 109 (1,000,000,000)
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Electromagnetic Spectrum
Gamma Rays
Infrared
Microwave
Visible
X-Rays
Radio
UV
30 cm
15.0 mm
0.03 nm
300 nm
380 nm
720 nm
VISIBLE LIGHT Violet 400 - 446 nm Blue 446
- 500 nm Green 500 - 578 nm Yellow 578 -
592 nm Orange 592 - 620 nm Red 620 -
700 nm
Angstrom 10-10 m nm 10-9 m mm 10-6 m cm
10-2 m km 1000 m
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Radiation Laws
1. Planks law
c is the speed of light, 3108 m/s ? is the
frequency T is temperature, in Kevin h is Plank
constant K is Boltzmann constant
Wavelength c/?
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Radiation Laws
3. Wiens law l 2,897.8/T
l wavelength (mm) at which radiance is at a
maximum
As objects become hotter, the wavelength
of maximum emittance shifts to shorter
wavelengths.
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Radiation Laws
3. Stefan-Boltzmanns law W sT 4
W total emitted radiation (watt m-2)
s Stefan-Boltzmann constant (5.6697x10-8 W m-2
K-4)
T temperature in Kelvin (T in Kelvin 273.15
oC)
Hot blackbodies emit more energy per unit area
than do cold blackbodies
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Radiation Laws
4. Kirchhoffs law e M/Mb
e emissivity a measure of the effectiveness of
an object as a
radiator of electromagnetic energy (0-1)
M emittance of a given object
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Radiation Laws
5. Radiant Energy Conservation Law
Absorption Reflection Transmission Incoming
Radiation
Incoming
reflection
absorption
transmission
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Radiation Laws
6. Cosines Law
Es Ep cos?

1.0
cos ?
0
90?
0?
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Interaction with the Atmosphere
Scattering
Blue sky and red-orange sunset
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Scattering
Specks of dust, N2 and O2 molecules
Rayleigh
l -4

Strongly wavelength dependent
Mie
Dust, pollen, smoke, water droplets
Weakly wavelength dependent
Nonselective
Larger water droplets, large particles of
airborne dust
Wavelength independent
Scattering decreases the quality of an image
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Electromagnetic Radiation
Io
Is
ID
ID


Io
I
Is
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Interaction with the Atmosphere
Absorption
of radiation occurs when the
atmosphere prevents, or strongly attenuates,
transmission of radiation or its energy through
the atmosphere.
Ozone (O3) Carbone Dioxyde (CO2) Water Vapor
(H2O)
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Interaction with the Atmosphere
Atmospheric Windows
Absorption
UV Visible 0.30-0.75 mm
0.77-0.91 mm
Near infrared
mid- Infrared 1.55-1.75 mm
2.05-2.40 mm
Thermal IR 8.0-9.2 mm
10.2-12.4 mm
Microwave 7.5-11.5 mm
20.0 mm
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Typical values for the Earth as a whole.
Solar Radiation (Shortwave)
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Terrestrial Radiation (Longwave gt 10mm)
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Interaction with Surfaces
Reflection
Specular reflection
Diffuse (isotropic) reflection
Water bodies
Lambertian surface
Mirror-type surface
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Interaction with Surfaces
Transmission
Non-selective
selective
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Radiation Terminology (1)

• Radiant Energy total radiation energy
• in Joules (J)
• 2. Radiant flux Radiant energy per unit time
• in J/s
• 3. Radiant flux density Radiant flux per unit
  surface area
• in J/(m2 s) or W/m2

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Radiation Terminology (2)
4. Irradiance Radiant flux density. It refers to
fluxes to or from a flat surface in
all directions in J/(m2 s) 5. Radiance
Radiant flux density per unit solid angle.
It refers to fluxes to or from a surface
in a specific direction in J/(m2 s
sr) 6. Spectral Radiance Radiant flux per unit
wavelength in J/(m2 s sr ?m)
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Radiation Terminology (3)
7. Albedo Reflected radiant flux density
(irradiance) divided by
incoming radiant flux density (irradiance)
from a flat surface in all directions
unitless 8. Reflectance Reflected radiance
in one direction
(in J/(m2 s sr) times ? (in sr) divided
by incoming radiant flux density (in J/(m2
s)) unitless
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Interaction with the Atmosphere
Refraction