Test 1

• Atmospheric effects on radiant temperature measurements

  • Gases and suspended particles in the atmosphere may absorb radiation emitted from ground objects, resulting in a decrease in the energy reaching a thermal sensor
  • Ground signals can also be attenuated by scattering in the presence of suspended particles
  • Gases and suspended particles in the atmosphere may emit radiation of their own, adding to the radiation sensed
• Atmospheric absorption and scattering


  Make the signals from ground objects appear colder than they are
• Atmospheric emission


  Makes ground objects appear warmer then they are
• Depending on atmospheric conditions during imaging, one of these effects will outweigh the other, resulting in a biased sensor output
• Both atmospheric absorption/scattering and emission effects are directly related to the atmospheric path length, or distance through which the radiation is sensed
• The atmosphere has a significant effect on the intensity and spectral composition of the energy recorded by a thermal system
• Atmospheric windows influence the selection of the optimum spectral bands within which to measure thermal energy signals
• Blackbody


  An ideal material that completely absorbs all incident radiation, converting it to internal energy. It does not permit any transmittance or reflectance but emits (re-radiates) the absorbed energy at the maximum possible rate per unit area
• The amount of radiant energy emitted by a blackbody varies with temperature and wavelength(s)
• Any object having a temperature greater than absolute zero (0 K, or –2730C) emits radiation whose intensity and spectral composition are a function of the material type involved and the temperature of the object under consideration
• Energy incident on the surface of a terrain element (EI)


  Can be absorbed (EA), reflected (ER), or transmitted (ET)