Electromagnetic Radiation EMR

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Electromagnetic Radiation(EMR)
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Remote Sensing Uses EMR!Soyou need to
understand

• Basic physics of EMR
• Units used to describe EMR
• Divisions of EMR spectrum
• Behavior of EMR interacting with the atmosphere
  and other materials

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• All objects warmer than absolute zero emit EMR
• Most objects reflect EMR emitted by other objects
• Key basis of remote sensing because objects of
  interest interact in unique ways with EMR

Photo from Flickr by noqontrol
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How do we describe EMR?

• Wavelength
• Frequency
• Energy

Photo from Flickr lolapaipro
Photo from Flickr by neon360
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Structure of electromagnetic radiation
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Wavelength
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Wavelength Units

• Meters (m)
• Centimeters (cm)
• Millimeters (mm)
• Micrometers (µm)
• Nanometers (nm)
• Angstroms (?)

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Frequency

• The number of waves that pass through an
  imaginary plane in a specific amount of time
  (e.g., 1 second)

Photo from Flickr by Patrick Treehouse
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Frequency Units

• Hertz (Hz)
• Kilohertz (KHz)
• Megahertz (MHz)
• Gigahertz (GHz)
• Etc.

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Velocity of Light (c)

• c wavelength x frequency (??)
• c 3 x 108 m/sec (the speed of light)
• 186,000 miles/sec

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Energy (Q)
Q h ? Q Energy of a quantum (joules) h
Plancks constant (6.626 10-34 J s) ?
Frequency So Energy is proportional to
frequency Energy is inversely proportional to
wavelength
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Frequency-Wavelength-Energy
Web Demo Electromagnetic Waves
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The EMR Spectrum
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Electromagnetic Spectrum
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Visible Light

• Wavelengths that dominate radiation given off by
  the sun
• Most animals evolved to see these wavelengths
• Captured by your digital camera

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Additive Primaries (Color Theory) (Add together
in different proportions to make all other colors)
Red Blue Magenta Red Green Yellow Blue
Green Cyan Red Blue Green White
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Why is Color Theory Important?

• Your computer screen uses the 3 additive
  primaries to display all possible colors
• To interpret remotely sensed imagery you must be
  able to interpret color

Photo from Flickr (by pixel eight)
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Infrared Portion of the Spectrum
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Infrared Radiation

• Near Infrared (NIR) 720 1300 nm
• Mid Infrared (MIR) 1300 3000 nm
• Far Infrared (FIR) 3000 nm

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Other parts of the Spectrum
UV
Radar
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Atmospheric Effects

• Absorption
• Scattering (will discuss later in the semester)

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Absorption

• Prevention or strong attenuation of the
  transmission of radiant energy through the
  atmosphere
• Especially important Ozone (O3), Carbon Dioxide
  (CO2), Water vapor (H2O)

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Transmission (opposite of aborption)

• Transmittance (t) Transmitted/Incident
• Varies with wavelength
• Atmospheric transmittance varies depending on
  atmospheric conditions for each wavelength

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Absorption
Ozone Hole
Thermal IR Greenhouse Effect
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Ozone

• Absorbs strongly in the UV (short wavelengths)
• Protects us from skin cancer!

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Carbon Dioxide

• Absorbs in mid and far infrared
• Greenhouse effect!

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Water Vapor

• Very strong absorber in 5.5-7.0 um range
• Very strong absorber 27 um
• Variable in time and space

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Clouds!

• Most EMR wavelengths cant penetrate clouds
• Big problem in remotely sensed imagerytropics
  especially
• Temporal compositing to get rid of clouds
• Cloud shadows a problem too

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Riverton Landsat Image July 15 1999 Cloudy!
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Summary

• All of this is important because it determines in
  part how objects of interest interact with EMR
  which is what we use in remote sensing. The
  better we understand these interactions, the
  better we are at using the remote sensing tool!