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Remote Sensing Thermal Remote Sensing

Remote Sensing Thermal Remote Sensing. 1. Review of Radiation Laws. All objects at temperature above absolute 0 o K emit (-273.59 o C, -459.67 o F) Stefan-Boltzmann law: W = s T 4   W-total emitted radiation s -a constant, T-temperature in o K

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Remote Sensing Thermal Remote Sensing

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  1. Remote SensingThermal Remote Sensing

  2. 1. Review of Radiation Laws • All objects at temperature above absolute 0oK emit (-273.59oC, -459.67oF) • Stefan-Boltzmann law: W = sT4  W-total emitted radiation s-a constant, T-temperature in oK •  The total emitted radiation from a blackbody is proportional to the fourth power of its absolute temperature

  3. Radiation Laws • Wien's displacement law: l = 2,897.8/T l-peak wavelength, T-temperature in oK •  As temperature of objects increases, the wavelength of peak emittance becomes shorter

  4. Radiation Laws • Emissivity: e = M/Mb   e-emissivity M-emittance of a given object   Mb-emittance of blackbody   e = 1 (blackbody)   e = 0 (whitebody, perfect reflector) •  The ratio between the emittance of a given object and that of blackbody at the same temperature

  5. Emissivity of Common Materials Dry mineral soil 0.92-0.94 paint 0.90-0.96 Dry vegetation 0.88-0.94 Dry snow 0.85-0.90 Granite rock 0.83-0.87 Glass 0.77-0.81 Sheet iron (rusted) 0.63-0.70 Polished metals 0.16-0.21 Aluminum foil 0.03-0.07 Highly polished gold 0.02-0.03 Clear water 0.98-0.99 Wet snow 0.98-0.99 Human skin 0.97-0.99 Rough ice 0.97-0.98 Vegetation 0.96-0.99 Wet soil 0.95-0.98 Asphalt concrete 0.94-0.97 Brick 0.93-0.94 Wood 0.93-0.94 Basalt rock 0.92-0.96

  6. 2. Heat • Kinetic temperature         • Radiant temperature • Heat capacity • Specific heat • Thermal conductivity

  7. Heat .. • Kinetic temperature (oF oC oK)  - thermal energy of molecules within a substance •  Radiant temperature  - the emitted energy

  8. Heat .. • Heat capacity C (cal·g-1·oC-1)  - the ratio of the change in heat energy per unit mass to the corresponding change in temperature at constant pressure • Water has a higher heat capacity than many other materials

  9. Heat .. • It takes more energy for water to warm up to the same temperature than many other materials do • Rank of heat capacity Water > forest > grass > land • In other words, for a given amount of energy, water warms up slower than many other materials

  10. Heat .. • Specific heat  - the ratio of the heat capacity of a substance to that of a reference substance, i.e. pure water • Specific heat of water = 1 Specific heat for many other materials < 1

  11. Heat .. • Thermal conductivity K (cal·cm-1 ·sec-1·oC-1)  - the rate at that a substance transfers heat • Water has a lower K value than many other materials • It takes a longer time for water to transfer heat over a given distance than many other materials

  12. 3. Geometry of Thermal Images • Tangential scale distortion  - caused by varied viewing distance • Aircraft instability - roll: side by side motion - crab (yaw): by compensating drift   - pitch: head/tail motion

  13. Geometry of Thermal Images • Relief displacement  - differs from that of aerial photography   - vertical features on thermal images displaced from the nadir for each scan - vertical features on air photo displaced radially from the principal point

  14. 4. Thermal Image Interpretation • Limitations  - thermal images contain noise and errors     - differences in emitted energy is not directly related to differences in temperature, must know emissivity of each material     - sensors only record the radiance at the surface

  15. Color-coded temperature maps derived from NIMBUS http://rst.gsfc.nasa.gov/Sect14/Sect14_4.html

  16. Landsat band 6 full scene acquired at 9:32 P.M. on August 22, 1982

  17. Thermal Image Interpretation • Landscape factors • Timing   

  18. Thermal Image Interpretation • Landscape factors      - surface material: land vs. water         - topography: sunlit vs. shadowed         - vegetation cover: land, grass, forest, water         - moisture

  19. Thermal Image Interpretation • Timing Early afternoon: - high thermal contrast but with thermal shadow and slope orientation effects - water is cool; bare soil, meadow and forest are warmer

  20. Thermal Image Interpretation • Timing  Before dawn:  - lower thermal contrast but little slope orientation effects or thermal shadow  - water is warm; open meadow and bare soil are cool, forests are warm

  21. Thermal Image Interpretation .. • Radiant temperature fluctuates less for water than for many other materials due to its high heat capacity • Radiant temperature peaks later for water than for many other materials due to its high heat capacity

  22. Readings • Chapter 5

  23. Spectral Reflectance Curve

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