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• EMR


  Electromagnetic radiation

  
• Remote sensing


  Detector measures the EM radiation/energy that is reflected/emitted from the Earth's surface materials

  
• Travel time from the Sun to Earth is about 8 minutes
• Electromagnetic radiation


  Energy consisting of an electrical (E) and magnetic (M) fields oriented at right angles with each other that travels through atmosphere at the speed of light (c) and at a certain wavelength (λ)

  
• Electromagnetic radiation


  • Characterised by frequency (v) or wavelength (λ)
  • v = c / λ where c=3x108 m/s

  
• Frequency (v)


  • Number of cycles of a wave passing a fixed point per unit of time
  • Unit: hertz(Hz), equivalent to one cycle per second
  • Changes as EMR propagates through media of different densities
• Wavelength (λ)


  Length of one wave cycle
• Amplitude (A)


  Magnitude of oscillation from the mean value
• Frequency and wavelength


  Frequency is inversely proportional to wavelength
• Electromagnetic spectrum


  Continuum of energy that ranges from meters to nanometers in wavelength, travels at the speed of light, and propagates through a vacuum such as outer space

  
• Radiant flux (Φ)


  Rate of radiometric energy per unit time

  
• Radiant flux density (E or M)


  Radiant flux that flows through unit area of a surface
• Radiance (L)


  Radiant flux per unit solid angle leaving an extended source in a given direction per unit projected source area in that direction

  
• Ultraviolet (UV)


  Very narrow zone of EMR with short wavelengths, largely scattered by atmospheric particles
• Visible


  Regions of EMR that can be perceived by human eyes, with blue, green and red as the primary colors
• Near Infrared (NIR)


  Frequently used in Remote Sensing
• Middle Infrared (MIR)


  Comprises of SWIR (1.5-3 μm) and MIR (3.0-5.0 μm), both highly used in Remote Sensing
• Thermal Infrared (TIR)


  Long wavelengths, much of this energy is comprised of emitted radiation from the Earth

  
• Microwave


  Longest wavelengths used in Remote Sensing, used in both Active and Passive modes, can penetrate into clouds and fog
• Energy of EM directly proportional to frequency, energy determines interaction with matter
• Blackbody


  Hypothetical ideal radiator that totally absorbs and reemits all energy upon it
• Blackbody radiation


  Emitted by all matter having a temperature above absolute zero (0 K), intensity and spectral composition are a function of the material type and temperature
• Emissivity


  Ratio between the emittance of a given object and that of the blackbody at the same temperature, effectiveness of a surface in emitting energy as thermal radiation

  
• Emissivity of various materials

  • Water is a good approximation of a blackbody (grey body), quartz is not a good approximation (selective radiator)

  
• Solar radiation


  Solar energy which passes through the atmosphere and is reflected in varying degrees by Earth's surface and atmosphere, detectable only during daylight

  • shortwave radiation
• Terrestrial radiation


  Energy emitted from the earth and atmosphere, detectable both day and night, essentially all energy is radiated at thermal infrared wavelengths between 4-25μm

  • longwave radiation

  
• Troposphere


  Layer characterized by a decrease in temperature with respect to height, up to about 10 km, where all weather activities occur

  
• Stratosphere


  Layer where temperature is approximately constant in the lower 20 km, then increases with height up to about 50 km, where ozone exists mainly

  
• Mesosphere


  Layer where temperature decreases from about 50 km to 85 km

  
• Thermosphere


  Layer extending from about 85 km upward to several hundred kilometers, with temperature ranging from 500 K to 2000 K

  
• Sun


  Emits energy in a range of wavelengths centered on the visible bands

  
• Energy enters the atmosphere


  Selectively scattered and/or absorbed

  
• Atmosphere


  • Affects not only the speed of radiation, but also its wavelength, its intensity, and its spectral distribution
  • EMR may also be diverted from its original direction due to refraction

  
• Interactions

  • Refraction
  • Scattering
  • Absorption
  • Reflection
• Solar radiation


  Passes through Earth's atmosphere and is reflected to varying degrees

  
• Terrestrial Radiation


  About half of solar radiation makes it to the surface, where it is absorbed and re-emitted continuously

  
• Three kinds of EMR-atmosphere interactions


  • Refraction
  • Absorption
  • Scattering

  
• Refraction


  The bending of light when it passes from one medium to another of different density

  
• Index of Refraction, n


  Measure of the optical density of a substance

  
• Index of refraction of atmosphere = 1.0002926