1. Thermal Infrared Remote Sensing Radiant versus Kinetic temperature Blackbody radiation Atmospheric effect Principle of energy conservation Radiation from Real Materials Kirchhoff radiation law

2. Selected Applications of Thermal Infrared Remote Sensing Selected Applications of Thermal Infrared Remote Sensing

3. Thermal Infrared Remote Sensing is emitted from all objects that have a  Thermal infrared EM radiation is emitted from all objects that have a temperature greater than absolute zero (K). temperature greater than absolute zero (K).  Our eyes cannot detect differences in thermal infrared energy because they are primarily sensitive to short wavelength visible light because they are primarily sensitive to short wavelength visible light from 0.4  m to 0.7  m. from 0.4  m to 0.7  m.  Thermal infrared sensors are sensitive to thermal infrared radiation ( 3.0 - 14 µm ). radiation ( 3.0 - 14 µm ). is emitted from all objects that have a  Thermal infrared EM radiation is emitted from all objects that have a temperature greater than absolute zero (K). temperature greater than absolute zero (K).  Our eyes cannot detect differences in thermal infrared energy because they are primarily sensitive to short wavelength visible light because they are primarily sensitive to short wavelength visible light from 0.4  m to 0.7  m. from 0.4  m to 0.7  m.  Thermal infrared sensors are sensitive to thermal infrared radiation ( 3.0 - 14 µm ). radiation ( 3.0 - 14 µm ).

4. Kinetic versus Radiant Temperature The energy of particles of matter in random motion is called kinetic heat (also referred to as internal or true heat). All objects having a temperature above absolute zero (0 ˚K; or -273.16 ˚C) exhibit this random motion. The energy of particles of matter in random motion is called kinetic heat (also referred to as internal or true heat). All objects having a temperature above absolute zero (0 ˚K; or -273.16 ˚C) exhibit this random motion. The amount of kinetic heat can be measured in kinetic temperature (T kin ) using a thermometer through direct contact with the object. The amount of kinetic heat can be measured in kinetic temperature (T kin ) using a thermometer through direct contact with the object. The energy of particles of matter in random motion is called kinetic heat (also referred to as internal or true heat). All objects having a temperature above absolute zero (0 ˚K; or -273.16 ˚C) exhibit this random motion. The energy of particles of matter in random motion is called kinetic heat (also referred to as internal or true heat). All objects having a temperature above absolute zero (0 ˚K; or -273.16 ˚C) exhibit this random motion. The amount of kinetic heat can be measured in kinetic temperature (T kin ) using a thermometer through direct contact with the object. The amount of kinetic heat can be measured in kinetic temperature (T kin ) using a thermometer through direct contact with the object.

5. Kinetic versus Radiant Temperature The electromagnetic radiation exiting an object is called radiant exitance (  ). The electromagnetic radiation exiting an object is called radiant exitance (  ). The concentration of the amount of radiant exitance emitted from an object is its radiant temperature (T rad ). The concentration of the amount of radiant exitance emitted from an object is its radiant temperature (T rad ). There is a high positive correlation between the kinetic temperature of an object (T kin ) and radiant temperature (T rad ). There is a high positive correlation between the kinetic temperature of an object (T kin ) and radiant temperature (T rad ). Therefore, we can utilize radiometers placed some distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. This is the basis of thermal infrared remote sensing.Therefore, we can utilize radiometers placed some distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. This is the basis of thermal infrared remote sensing. The electromagnetic radiation exiting an object is called radiant exitance (  ). The electromagnetic radiation exiting an object is called radiant exitance (  ). The concentration of the amount of radiant exitance emitted from an object is its radiant temperature (T rad ). The concentration of the amount of radiant exitance emitted from an object is its radiant temperature (T rad ). There is a high positive correlation between the kinetic temperature of an object (T kin ) and radiant temperature (T rad ). There is a high positive correlation between the kinetic temperature of an object (T kin ) and radiant temperature (T rad ). Therefore, we can utilize radiometers placed some distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. This is the basis of thermal infrared remote sensing.Therefore, we can utilize radiometers placed some distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. This is the basis of thermal infrared remote sensing.

6. Thermal Infrared Atmospheric Windows The atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called atmospheric windows. The atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called atmospheric windows. EM spectrum regions that absorb most of the infrared energy are called absorption bands. Water vapor (H 2 O), carbon dioxide (CO 2 ), and ozone (O 3 ) are responsible for most of the absorption. For example, atmospheric water vapor (H 2 O) absorbs most of the energy exiting the terrain in the region from 5 to 7  m making it almost useless for remote sensing. The atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called atmospheric windows. The atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called atmospheric windows. EM spectrum regions that absorb most of the infrared energy are called absorption bands. Water vapor (H 2 O), carbon dioxide (CO 2 ), and ozone (O 3 ) are responsible for most of the absorption. For example, atmospheric water vapor (H 2 O) absorbs most of the energy exiting the terrain in the region from 5 to 7  m making it almost useless for remote sensing.

7. Atmospheric Windows in the Electromagnetic Spectrum

8. Thermal Infrared Detectors TIR detectors are made sensitive to thermal infrared radiant energy exiting the terrain in the two primary thermal infrared windows: and 8 - 14  m. TIR detectors are made sensitive to thermal infrared radiant energy exiting the terrain in the two primary thermal infrared windows: 3 - 5  m and 8 - 14  m. The Earth’s ozone (O 3 ) layer absorbs much of the thermal energy exiting the terrain in an absorption band from approximately 9 - 10  m. Therefore, satellite thermal infrared remote sensing systems usually only record data in the region from 10.5 - 12.5  m to avoid the absorption band. The Earth’s ozone (O 3 ) layer absorbs much of the thermal energy exiting the terrain in an absorption band from approximately 9 - 10  m. Therefore, satellite thermal infrared remote sensing systems usually only record data in the region from 10.5 - 12.5  m to avoid the absorption band. TIR detectors are made sensitive to thermal infrared radiant energy exiting the terrain in the two primary thermal infrared windows: and 8 - 14  m. TIR detectors are made sensitive to thermal infrared radiant energy exiting the terrain in the two primary thermal infrared windows: 3 - 5  m and 8 - 14  m. The Earth’s ozone (O 3 ) layer absorbs much of the thermal energy exiting the terrain in an absorption band from approximately 9 - 10  m. Therefore, satellite thermal infrared remote sensing systems usually only record data in the region from 10.5 - 12.5  m to avoid the absorption band. The Earth’s ozone (O 3 ) layer absorbs much of the thermal energy exiting the terrain in an absorption band from approximately 9 - 10  m. Therefore, satellite thermal infrared remote sensing systems usually only record data in the region from 10.5 - 12.5  m to avoid the absorption band.

9. Thermal Radiation Laws A blackbody is a hypothetical, ideal radiator that totally absorbs and reemits all energy incident upon it. A blackbody is a hypothetical, ideal radiator that totally absorbs and reemits all energy incident upon it. No objects in nature are true blackbodies, however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody. No objects in nature are true blackbodies, however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody. A blackbody is a hypothetical, ideal radiator that totally absorbs and reemits all energy incident upon it. A blackbody is a hypothetical, ideal radiator that totally absorbs and reemits all energy incident upon it. No objects in nature are true blackbodies, however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody. No objects in nature are true blackbodies, however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody.

10. Blackbody Radiation Curves for Several Objects including the Sun and Earth

11. The relationship between the kinetic temperature of a blackbody (T) and its dominant wavelength ( m ) where peak exitance occurs is described by Wein’s displacement law: Wein’s Displacement Law

12. For example, the average temperature of the Earth is 300 ˚K (80 ˚F). We compute the Earth’s dominant wavelength as: max = 2898  m ˚K max = 2898  m ˚K T max = 2898  m ˚K = 9.67  m max = 2898  m ˚K = 9.67  m 300 ˚K 300 ˚K For example, the average temperature of the Earth is 300 ˚K (80 ˚F). We compute the Earth’s dominant wavelength as: max = 2898  m ˚K max = 2898  m ˚K T max = 2898  m ˚K = 9.67  m max = 2898  m ˚K = 9.67  m 300 ˚K 300 ˚K Wein’s Displacement Law

13. The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 ˚K forest fires that have a dominant wavelength of approximately 3.62  m then the most appropriate remote sensing system might be a thermal infrared detector. The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 ˚K forest fires that have a dominant wavelength of approximately 3.62  m then the most appropriate remote sensing system might be a 3-5  m thermal infrared detector. If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K and a dominant wavelength of 9.66  m, then a thermal infrared detector operating in the 8 - 14  m region might be most appropriate. If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K and a dominant wavelength of 9.66  m, then a thermal infrared detector operating in the 8 - 14  m region might be most appropriate. The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 ˚K forest fires that have a dominant wavelength of approximately 3.62  m then the most appropriate remote sensing system might be a thermal infrared detector. The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 ˚K forest fires that have a dominant wavelength of approximately 3.62  m then the most appropriate remote sensing system might be a 3-5  m thermal infrared detector. If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K and a dominant wavelength of 9.66  m, then a thermal infrared detector operating in the 8 - 14  m region might be most appropriate. If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K and a dominant wavelength of 9.66  m, then a thermal infrared detector operating in the 8 - 14  m region might be most appropriate. Wein’s Displacement Law

14. Developments from Planck’s Law: Stefan-Boltzmann Law The area under the Planck curve represents the total energy (M) emitted by an object at a given temperature (T) The Stefan-Boltzmann law calculate this energy for a blackbody at a given temperature (T).

15. Total radiant exitance (M) leaving the surface of a blackbody is proportional to the fourth power of its temperature (T). This is the Stefan- Boltzmann law. where σ is the Stefan-Boltzmann constant, 5.6697 x 10-8 W m-2 K-4. Thus the remote measurement of radiant exitance M from a surface can be used to infer the temperature T of the surface. It is this indirect approach to temperature measurement that is used in thermal sensing. Total radiant exitance (M) leaving the surface of a blackbody is proportional to the fourth power of its temperature (T). This is the Stefan- Boltzmann law. where σ is the Stefan-Boltzmann constant, 5.6697 x 10-8 W m-2 K-4. Thus the remote measurement of radiant exitance M from a surface can be used to infer the temperature T of the surface. It is this indirect approach to temperature measurement that is used in thermal sensing. Stephen Boltzmann Law

16. Real objects (such as rocks, soil, and water) emit only a fraction of the energy emitted from a blackbody at the same temperature. Real objects (such as rocks, soil, and water) emit only a fraction of the energy emitted from a blackbody at the same temperature. Emissivity, , is the ratio between the radiant exitance emitting from a real-world object and that from a blackbody at the same temperature: Emissivity, , is the ratio between the radiant exitance emitting from a real-world object and that from a blackbody at the same temperature: Real objects (such as rocks, soil, and water) emit only a fraction of the energy emitted from a blackbody at the same temperature. Real objects (such as rocks, soil, and water) emit only a fraction of the energy emitted from a blackbody at the same temperature. Emissivity, , is the ratio between the radiant exitance emitting from a real-world object and that from a blackbody at the same temperature: Emissivity, , is the ratio between the radiant exitance emitting from a real-world object and that from a blackbody at the same temperature: Radiation from real Materials & Emissivity

17. All real world materials have emissivities ranging from 0 to <1 that fluctuate depending upon the wavelengths of energy being considered. A graybody outputs a constant emissivity that is less than one at all wavelengths. Some materials like water have emissivities close to one (0.99) over the wavelength interval from 8 - 14  m. Others such as polished aluminum (0.08) and stainless steel (0.16) have very low emissivities. All real world materials have emissivities ranging from 0 to <1 that fluctuate depending upon the wavelengths of energy being considered. A graybody outputs a constant emissivity that is less than one at all wavelengths. Some materials like water have emissivities close to one (0.99) over the wavelength interval from 8 - 14  m. Others such as polished aluminum (0.08) and stainless steel (0.16) have very low emissivities. EmissivityEmissivity

18. Spectral emissivity of a blackbody, a graybody, and a hypothetical selective radiator 2x reduction Spectral radiant exitance distribution of the blackbody, graybody, and hypothetical selective radiator Spectral Emissivity,  Spectral Radiant Exitance W m -2 um -1

19. Two objects lying next to one another on the ground could have the same kinetic temperature but have different radiant temperatures when sensed by a thermal radiometer simply because their emissivities are different. The emissivity of an object may be influenced by a number factors, e.g. - color -- darker colored objects are usually better absorbers and emitters (i.e. they have a higher emissivity than lighter colored objects which tend to reflect more of the incident energy. - moisture content -- the more moisture an object contains, the greater its ability to absorb energy and become a good emitter. Wet soil particles have a high emissivity similar to water. Two objects lying next to one another on the ground could have the same kinetic temperature but have different radiant temperatures when sensed by a thermal radiometer simply because their emissivities are different. The emissivity of an object may be influenced by a number factors, e.g. - color -- darker colored objects are usually better absorbers and emitters (i.e. they have a higher emissivity than lighter colored objects which tend to reflect more of the incident energy. - moisture content -- the more moisture an object contains, the greater its ability to absorb energy and become a good emitter. Wet soil particles have a high emissivity similar to water. EmissivityEmissivity

20. Incident (incoming) energy (  i ) is equal to the sum of the amount of energy reflected from the surface (  r ), the amount of energy absorbed by the surface (  a ), and the amount of energy transmitted through the surface (  t ).  i =  r +   +   Incident (incoming) energy (  i ) is equal to the sum of the amount of energy reflected from the surface (  r ), the amount of energy absorbed by the surface (  a ), and the amount of energy transmitted through the surface (  t ).  i =  r +   +   Principle of Energy Conservation

21. Dividing each of the variables by the original incident energy:  i /  i = (  r /  i ) +(   /  i ) +(   /  i ) allows us to rewrite the initial equation as:  = r  +  +  where r is spectral reflectance by the terrain,  is spectral absorptance, and  is spectral transmittance. Dividing each of the variables by the original incident energy:  i /  i = (  r /  i ) +(   /  i ) +(   /  i ) allows us to rewrite the initial equation as:  = r  +  +  where r is spectral reflectance by the terrain,  is spectral absorptance, and  is spectral transmittance.

22. The Russian physicist Kirchhoff found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e.  ~ . This is often phrased as: The Russian physicist Kirchhoff found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e.  ~ . This is often phrased as: “good absorbers are good emitters”. “good absorbers are good emitters”. In most remote sensing applications, objects are usually opaque to thermal radiation. Therefore, we may assume transmittance,  = 0. Substituting emissivity for absorptance and removing transmittance from the equation yields: In most remote sensing applications, objects are usually opaque to thermal radiation. Therefore, we may assume transmittance,  = 0. Substituting emissivity for absorptance and removing transmittance from the equation yields:  = r  +   = r  +  The Russian physicist Kirchhoff found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e.  ~ . This is often phrased as: The Russian physicist Kirchhoff found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e.  ~ . This is often phrased as: “good absorbers are good emitters”. “good absorbers are good emitters”. In most remote sensing applications, objects are usually opaque to thermal radiation. Therefore, we may assume transmittance,  = 0. Substituting emissivity for absorptance and removing transmittance from the equation yields: In most remote sensing applications, objects are usually opaque to thermal radiation. Therefore, we may assume transmittance,  = 0. Substituting emissivity for absorptance and removing transmittance from the equation yields:  = r  +   = r  +  Kirchoff’s Radiation Law

23. If reflectivity increases then emissivity must decrease. If emissivity increases then reflectivity must decrease. If reflectivity increases then emissivity must decrease. If emissivity increases then reflectivity must decrease. For example, water absorbs almost all incident energy and reflects very little. Therefore, water is a very good emitter and has a high emissivity close to 1. Conversely, a sheet metal roof reflects most of the incident energy, absorbs very little, yielding an emissivity much less than 1. For example, water absorbs almost all incident energy and reflects very little. Therefore, water is a very good emitter and has a high emissivity close to 1. Conversely, a sheet metal roof reflects most of the incident energy, absorbs very little, yielding an emissivity much less than 1. Therefore, metal objects such as cars, aircraft, and metal roofs almost always look very cold (dark) on thermal infrared imagery. Therefore, metal objects such as cars, aircraft, and metal roofs almost always look very cold (dark) on thermal infrared imagery. If reflectivity increases then emissivity must decrease. If emissivity increases then reflectivity must decrease. If reflectivity increases then emissivity must decrease. If emissivity increases then reflectivity must decrease. For example, water absorbs almost all incident energy and reflects very little. Therefore, water is a very good emitter and has a high emissivity close to 1. Conversely, a sheet metal roof reflects most of the incident energy, absorbs very little, yielding an emissivity much less than 1. For example, water absorbs almost all incident energy and reflects very little. Therefore, water is a very good emitter and has a high emissivity close to 1. Conversely, a sheet metal roof reflects most of the incident energy, absorbs very little, yielding an emissivity much less than 1. Therefore, metal objects such as cars, aircraft, and metal roofs almost always look very cold (dark) on thermal infrared imagery. Therefore, metal objects such as cars, aircraft, and metal roofs almost always look very cold (dark) on thermal infrared imagery. Implications of Kirchoff’s Radiation Law

24. The radiant temperature of an object recorded by a remote sensor is related to its kinetic temperature and emissivity by the following relationship: The radiant temperature of an object recorded by a remote sensor is related to its kinetic temperature and emissivity by the following relationship: T rad =  1/4 T kin The radiant temperature of an object recorded by a remote sensor is related to its kinetic temperature and emissivity by the following relationship: The radiant temperature of an object recorded by a remote sensor is related to its kinetic temperature and emissivity by the following relationship: T rad =  1/4 T kin Relationship b/w T rad and T kin

25. The diameter of the circular ground area viewed by the sensor, D, is a function of the instantaneous-field-of-view, , of the scanner measured in milliradians (mrad) and the altitude of the scanner above ground level, H, where: The diameter of the circular ground area viewed by the sensor, D, is a function of the instantaneous-field-of-view, , of the scanner measured in milliradians (mrad) and the altitude of the scanner above ground level, H, where: D = H x  D = H x  For example, if the IFOV of the scanner is 2.5 mrad, the ground size of the pixel in meters is a product of the IFOV (0.0025) and the altitude above ground level (AGL) in meters. IFOVs range from 0.5 to 5 milliradians The diameter of the circular ground area viewed by the sensor, D, is a function of the instantaneous-field-of-view, , of the scanner measured in milliradians (mrad) and the altitude of the scanner above ground level, H, where: The diameter of the circular ground area viewed by the sensor, D, is a function of the instantaneous-field-of-view, , of the scanner measured in milliradians (mrad) and the altitude of the scanner above ground level, H, where: D = H x  D = H x  For example, if the IFOV of the scanner is 2.5 mrad, the ground size of the pixel in meters is a product of the IFOV (0.0025) and the altitude above ground level (AGL) in meters. IFOVs range from 0.5 to 5 milliradians Thermal Infrared Multispectral Scanners

26. Daytime Optical and Nighttime Thermal Infrared Imagery of New York City Thermal Infrared Aerial Photograph

27. Daytime Optical and Nighttime Thermal Infrared Imagery April April 26, 1981 4:56 am 1 x 1 m April April 26, 1981 4:56 am 1 x 1 m 2x reduction

28. Pre-dawn Thermal Infrared Image of Effluent Entering the Savannah River Swamp System March 31, 1981 4:28 am; 3 x 3 m March 31, 1981 4:28 am; 3 x 3 m Savannah River

29. Pre-dawn Thermal Infrared Image of a Residential Subdivision in Forth Worth, Texas Pre-dawn Thermal Infrared Image of a Residential Subdivision in Forth Worth, Texas 250 m AGL 1 mrad IFOV 6:45 am Jan 10, 1980 0.25 x 0.25 m 250 m AGL 1 mrad IFOV 6:45 am Jan 10, 1980 0.25 x 0.25 m

30. Nighttime Thermal Infrared Imagery of an Airport