Assignment 1

• Blackbody Radiation


  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
• Wien's Displacement Law


  1. T = A/λm

  2. Where, λm = wavelength of maximum spectral radiant exitance, expressed in m

  3. A = 2898 m K

  4. T = temperature, K
• According to Wien's Displacement Law, the Sun, with a photospheric radiant temperature of about 6000 °K, the peak radiation is in the visible domain (centered on 0.58 µm). A forest fire peaks at around 5.0 µm. The Earth, as observed from space, peaks within the 8-14 µm interval.
• Stefan – Boltzmann law


  1. M = σT^4

  2. Where M = total radiant exitance, Wm-2

  3. M(λ) = spectral radiant exitance, Wm-2 m-1

  4. σ = Stefan-Boltzmann constant, 5.6697 X 10-8 W m-2 K-4

  5. T = temperature of the blackbody, K
• Thermal scanner image


  A pictorial representation of the detector response on a line-by-line basis
• Thermal scanner


  • A particular kind of across-track multi-spectral scanner
  • Detector(s) only sense in the thermal portion of the spectrum (3 to 5 m or 8 to 14 m range of wavelengths)
  • Quantum or photon detectors are typically used
  • Detectors are capable of very rapid (less than 1sec) response
  • Detectors operate on the principle of direct interaction between photons radiation incident on them and the energy level of electrical charge carriers within the detector material
  • Detector must be cooled to temperatures approaching absolute zero to minimise their own thermal emissions
  • Detector is surrounded by a dewar containing liquid nitrogen at 77 K
• Thermal property of water

  • Water has very dark to medium grey tones in day thermal-IR images and moderately light tones in night thermal images
  • This response is due in part to a rather high thermal inertia, relative to typical land surfaces, as controlled largely by water's high specific heat
  • Water heats less during the day and holds that heat more at night
  • Being nonsolid, water in natural settings (rivers, lakes, oceans) is likely to experience disruption of its thermal gradient by convection (e.g., upwelling) and turbulence (e.g., wave action) that tend towards mixing and homogenation, so that its near-surface temperatures vary by only a few degrees at most (temperature "smoothing")
  • Water in moist soils tends to keep them cooler than drier soils
  • Water is very close (ε is 0.98 to 0.99) to behaving as a blackbody radiator in the 6 to 14 m range
• Blackbody


  Material that absorbs all colors of light and does not reflect or transmit any radiation
• Blackbody radiation


  Thermal heat of a body that must emit radiation at the same rate as it absorbs, so it must also be a good emitter of radiation, emitting electromagnetic waves off as many frequencies as it absorbs
• Blackbody radiation


  Emits electromagnetic waves off as many frequencies as it absorbs
• Wien's displacement law


  • Different temperature peaks at a wavelength that is inversely proportional to the temperature
  • Particular temperature is determined by spectral density of a curve
• As temperature rises


  A maximum wavelength is reached