The Atmosphere

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The Atmosphere

• Layers
• Composition

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Composition of air - Whats in it?

• Stable Components
• N2 78
• O2 21
• CO2 lt 1
• 100

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• Variable Components
• H2O Vapor highly variable (0 to 4)
• O3 - photochemical reactions

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Layers of the Atmosphere

• Troposhpere
• Where we live
• Weather
• 90 of total mass of atmosphere

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• Stratosphere
• Contains O3
• Absorbs ________??

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• Mesosphere
• Coldest layer
• Meteor dust act as cloud nuclei
• Thermosphere
• Warmest layer
• Ionosphere
• Absorbs cosmic rays, gamma rays, x-rays,
  shortest UV

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Effect of Atmosphere on EMR

• All solar emr passes through space to reach top
  of atmosphere, but not all reaches Earth's
  surface.
• Atmosphere scatters, absorbs and reflects a
  portion of in-coming solar radiation.
• Earth scatters, absorbs and reflects solar
  radiation that gets transmitted through the
  atmosphere.
• Finally - atmosphere scatters, absorbs and
  reflects the electromagnetic radiation that is
  reflected off the Earth's surface back toward the
  sensor.

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• Atm. Gases
• Critical to earth's energy balance through
  absorption and emission.
• Determines solar radiation reaching surface
• "windows"
• atm. effects are minimal
• allows ground-based measurements of celestial
  objects, and satellite-based measurements of
  earth's surface/atm.

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• Signal reaching the sensor may include reflection
  off Earth's surface that contains information,
  but it also includes in-coming and reflected EMR
  that has been scattered by the atmosphere.
• This can result in a loss of detail in the
  resulting images, making interpretation more
  difficult.

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Challenges of Remote Sensing

• 4 of in-coming solar radiation is reflected back
  from Earth's surface.
• 5 re-radiated after absorption as thermal IR.
• These two components are the focus of most
  terrestrial remote sensing.

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Challenges of Remote Sensing

• Only selected wavelengths are able to penetrate
  Earth's atmosphere and be reflected back to
  sensor.
• Thus, only some wavelengths are available for
  analysis and some objects of interest may not
  have unique spectral signatures within the set of
  available wavelengths.

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• Composition of atmosphere is important in
  understanding the role it plays in remote sensing
  and in interactions with electromagnetic
  radiation.
• largely a mixture of gases
• some with fairly constant concentrations
• others are variable in space and time.
• In addition - suspended particles (e.g. aerosol,
  smoke, ash etc.) and hydrometeors (e.g. cloud
  droplets, raindrops, snow, ice crystals, etc).
• About 99 of the mass lies below an altitude of
  30km.

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Table 1 composition of atmosphere below 100km.
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Main gases which absorb radiation.ultraviolet
(UV), visible, infrared (IR) and microwave
wavelengths.main spectral regions ("windows")
for which atmospheric absorption is small, are
listed at the bottom of the table.

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