Thermal Radiation

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Thermal Radiation
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• Sensitivity of detector is a significant variable
  in the design and operation of the system
• Low- coarse radiometric resolution
• High- fine radiometric resolution

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Thermal Radiometers
A radiometer is a sensor that measures the
intensity of radiation received within a
specified wavelength interval and within a
specific field of view
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Thermal Properties

• Emissivity is a ratio between emittance of an
  object in relation
• to emittance of blackbody at the same temperature
• A blackbody is a theoretical object that acts as
  a perfect absorber and emitter of radiation- it
  absorbs and reemits all energy that it receives

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• Emissivity varies from 0 1
• 1- thermal behavior identical to blackbody
• Graybody- emissivity less than 1.0 but has
  constant emissivity over all wavelengths
• Selective radiator- objects with an emissivity
  that varies with respect to wavelength

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Planck Radiation (Blackbody) Law
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Stefan-Boltzmann Law
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The Wien Displacement Law and Emissivity Effects

Wien's Law tells us that objects of different
temperature emit spectra that peak at different
wavelengths. ? m T C (2898)
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Thermal Image Interpretation
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The Heat Capacity Mapping Mission (HCMM) Weather
Satellites

• The Heat Capacity Mapping Mission (HCMM) was an
  experimental satellite program dedicated to
  determining how useful temperature measurements
  could be in identifying materials and thermal
  conditions on the land and sea.
• In service from April 1978 t0 September 1980
• Follow a near-polar, Sun-synchronous, retrograde
  orbit, at a nominal altitude of 620 km (385 mi)
• The repeat cycle varied 5 days, 16days 36 -hour
• a swath width of 715 km (445 mi) and a spatial
  resolution of 500 m (1640 ft) for the visible
  channel and 600 m (1968 ft) for the thermal
  channel

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The image uses color to portray Variations in
observed temperatures Major cities like New
York, Philadelphia, and Washington are Visible
as bright white areas near The coastline
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Thermography Night Vision Systems

• Thermal imaging, as well as use of specialized
  thermal detectors, has grown into an important
  technology that is applied directly by users on
  the ground or from low-flying aircraft
• The field is commonly called thermography
• Using thermal sensors coupled with optical
  systems, one is able to "see in the dark" by
  detecting varying temperatures from different
  objects in the scene
• Typical users include
• hunters and law enforcement officials
• military uses.
• check for heat loss from buildings
• thermal contamination in streams

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At the street level, this night scene shows
people, an auto, and houses in terms of relative
hotness
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A thermal snapshot of the Space Shuttle as it
landed at Cape Canavera