Lecture 5 Thermal Infrared Remote Sensing September 30, 2003

1. Lecture 5Thermal Infrared Remote SensingSeptember 30, 2003

2. Reading Assignment • Jensen – Chapter 8 Unless otherwise noted, all images in this lecture are from • Jensen, J.R., Remote Sensing of the Environment - An Earth Resource Perspective, 544 pp., Prentice Hall, Upper Saddle River, NJ, 2000.

3. AVHRR Image of land and sea surface temperature from thermal IR radiance measurements Red – warmest Orange Yellow Green Blue Purple - coldest Image from -http://rs.gso.uri.edu/amy/avhrr.html

7. Signature Detected by a Thermal Radiometer Thermal IR Radiometer Ls Lp  Lt  Ma emitted energy from the atmosphere Mt– emitted energy Target

8. Sources of surface temperature variations - gain and loss • Absorbed short-wavelength EM energy absorbed (from energy emitted from the sun) (heat gain) • Long-wavelength EM energy emitted from the earth’s surface (heat loss) • Combustion • Human vs. natural • Direct vs. indirect • Geothermal • Volcanoes • Hot springs

9. Stefan-Boltzman Law • The amount of EM radiation (M) emitted from a body in Watts m-2 (the exitance) can be calculated as M =  T4 where  is a constant and T4 is the temperature in degrees Kelvin

10. Wien Displacement Law • The wavelength with the highest level of emitted radiation (max) for an object of temperature T can be calculated as max = k / T where k = 2898 m ºK

11. T (sun) = 6000º K max = k / T = 2898/6000 = 0.483 m T (earth) = 300º K max = k / T = 2898/300 = 9.66 m Examples of Wien’s Displacement Law

12. Kinetic Heat - Tkin • Kinetic heat (internal or true heat) is the energy of particles of molecular matter in random motion • When particles collide, they generate radiant energy or electromagnetic radiation • Tkinis the true kinetic temperature, measured with a thermometer

13. Radiant Temperature - Trad •  - radiant flux – the amount of radiant energy per unit time pass through or from an object • Trad is simply the radiant flux being emitted by an object because of its temperature, i.e., the radiant temperature • Trad does not always equal Tkin

14. Perfect Radiator or Blackbody A theoretical object or surface that • Absorbs all the radiation that falls upon it • Radiates energy at the maximum rate possible at all wavelengths

15. Emissivity -  Emissivity defines the amount of radiation emitted from a body or surface (Mr ) relative to the exitance of a blackbody (Mb ) at the same temperature  = Mr / Mb

16. Factors influencing emissivity • Material • Surface roughness • Moisture content • Compaction • EM wavelength • Viewing angle

18. Graybody and Selective Emitters • Graybody emitters are those whose emittance is less than a perfect radiator with the same temperature, but whose emissions • are constant for any wavelength • are a consistent fraction of the perfect radiator or blackbody emittance • Selective emitters are bodies whose emittance is less than a perfect radiator or black body with the same temperature, but not constant as a function of wavelength

20. Kirchoff’s Radiation Law For any object that intercepts EM radiant energy r +  +  = 1 at thermal IR wavelengths,  = 0 and  =  Therefore 1 = r + 

21. Table 8-1 from text

22. Non-Blackbody Exitance • If a surface or body has an emissivity of , then its emittance, Mr, is Mr =   Tkin4 where • is the Stephan-Boltzman constant Tkin is the kinetic temperature

23. Apparent Radiant Temperature - Trad •  - radiant flux – the amount of radiant energy per unit time pass through or from an object • Trad is simply the radiant flux being emitted by an object because of its temperature, the radiant temperature

24. Radiant vs. Kinetic Temperature Trad = 1/4 Tkin

25. Sources of surface temperature variations - gain and loss • Short-wavelength EM energy absorbed from energy emitted from the sun • Long-wavelength EM energy emitted to the atmosphere • Combustion • Human vs. natural • Direct vs. indirect • Geothermal • Volcanoes • Hot springs

26. Sources of Signatures Detected by a Thermal Radiometer The Atmosphere - Thermal IR Radiometer Ls Eo • a-sw - absorption coefficient for shortwave EM radiation To – transmission coefficient Ed – path radiance Target  t-sw

27. a-sw

29. Sources of Signatures Detected by a Thermal Radiometer The Atmosphere - Thermal IR Radiometer Ls Eo Lt  • a-sw - absorption coefficient for shortwave EM radiation To – transmission coefficient Ed – path radiance Mt– emitted energy Target  t-sw, Tkin, 

31. Importance of albedo in thermal IR remote sensing • On the land and ocean surface, the sun provides most of the energy that results in variations in surface temperature • Albedo is the fraction of incoming solar radiation that is reflected from the earth’s surface • Surfaces with high albedo absorb little solar energy and therefore tend to have little thermal IR variability • Surfaces with low albedo absorb much energy, and have the potential for high thermal IR variability

32. Sources of Signatures Detected by a Thermal Radiometer The Atmosphere - Thermal IR Radiometer Ls Lt  • a-lw - absorption coefficient for longwave EM radiation Mt– emitted energy Target  t-sw, Tkin, 

33. a-lw

34. Signature Detected by a Thermal Radiometer Thermal IR Radiometer Ls Lp  Lt  Ma emitted energy from the atmosphere Mt– emitted energy Target

35. Signature Detected by a Thermal Radiometer Thermal IR Radiometer Ls Lp  Ma a-sw + a-lw  Ta Reflected thermal IR energy Target

36. Key Points for Lecture 6 • Reasons for channel selection in spaceborne thermal IR radiometers  atmospheric window • Minerology mapping • FLIR • Sources of thermal IR signatures from earth’s surface – role of short-wave and long-wave radiation • Diurnal thermal signatures • Principal of mapping fires using coarse-resolution thermal IR systems

37. Lecture Content • Spaceborne Thermal IR Radiometers • Forward Looking Infrared Radiometers (FLIRs) • Natural sources of surface temperature variations • Mapping of fires using coarse resolution systems

38. Spaceborne Thermal IR Radiometers • Landsat • AVHRR • MODIS • ASTER

39. Atmospheric Windows

43. Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) • ASTER was launched in December, 1999 • Jointly developed by U.S. and Japanese • 3 channels in the visible/near IR (reflectance) • 6 channels in the shortwave IR (reflectance) • 5 channels in the thermal IR (emittance) • Developed to discriminate different rock types (minerology)

45. http://www.ghcc.msfc.nasa.gov/precisionag/atlasremote.html

46. Emittance spectra of different minerals From: http://www.gps.caltech.edu/~ge151/ tutorials/tut_2.shtml

47. ASTER Image Red = B3 (.76-.86 um) Green = B2 (.63-.69 um) Blue = B1 (.52 -.59 um) NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

48. ASTER Image Red = B4 (1.6 – 1.7 um) Green = B6 (2.19 – 2.23 um) Blue = B8 (2.30 – 2.37 um) NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

49. ASTER Image Red = B13 (10.3-11.0 um) Green = B12 (8.9-9.3 um) Blue = B10 (8.1-8.5 um) NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team http://asterweb.jpl.nasa.gov/gallery/gallery. htm?name=Saline

50. Lecture Content • Spaceborne Thermal IR Radiometers • Forward Looking Infrared Radiometers (FLIRs) • Natural sources of surface temperature variations • Mapping of fires using coarse resolution systems