John R. Jensen Department of Geography University of South Carolina Columbia, South Carolina 29208 John R. Jensen Department of Geography University of

John R. JensenJohn R. JensenDepartment of GeographyDepartment of Geography

University of South CarolinaUniversity of South CarolinaColumbia, South Carolina 29208Columbia, South Carolina 29208

John R. JensenJohn R. JensenDepartment of GeographyDepartment of Geography

University of South CarolinaUniversity of South CarolinaColumbia, South Carolina 29208Columbia, South Carolina 29208

Thermal Infrared Remote SensingThermal Infrared Remote SensingThermal Infrared Remote SensingThermal Infrared Remote Sensing

Selected Applications of Thermal Infrared

Remote Sensing

Selected Applications of Thermal Infrared

Remote Sensing

Nighttime Thermal Infrared Imagery of an AirportNighttime Thermal Infrared Imagery of an AirportNighttime Thermal Infrared Imagery of an AirportNighttime Thermal Infrared Imagery of an Airport


Thermal infrared energyThermal infrared energy is emitted from all objects that have a is emitted from all objects that have a temperature greater than absolute zero. Therefore, all the features we temperature greater than absolute zero. Therefore, all the features we encounter in the landscape on a typical day (Sun, vegetation, soil, rocks, encounter in the landscape on a typical day (Sun, vegetation, soil, rocks, water, and even people) water, and even people) emitemit thermal infrared electromagnetic radiation. thermal infrared electromagnetic radiation. Humans sense thermal energy primarily through the sense of touch. Our Humans sense thermal energy primarily through the sense of touch. Our eyes cannot detect differences in thermal infrared energy because they are eyes cannot detect differences in thermal infrared energy because they are primarily sensitive to short wavelength visible light from 0.4 primarily sensitive to short wavelength visible light from 0.4 m to 0.7 m to 0.7 m. Our eyes are not sensitive to the m. Our eyes are not sensitive to the reflective infrared (0.7 - 3.0 reflective infrared (0.7 - 3.0 m) m) or or thermal infrared energy (3.0 - 14 thermal infrared energy (3.0 - 14 m)m). Fortunately, engineers have . Fortunately, engineers have developed developed detectorsdetectors that are sensitive to thermal infrared radiation. These that are sensitive to thermal infrared radiation. These thermal infrared sensors allow humans to sense a previously thermal infrared sensors allow humans to sense a previously invisible invisible world of information world of information as they monitor the as they monitor the thermal characteristics of the thermal characteristics of the landscape.landscape.

Thermal infrared energyThermal infrared energy is emitted from all objects that have a is emitted from all objects that have a temperature greater than absolute zero. Therefore, all the features we temperature greater than absolute zero. Therefore, all the features we encounter in the landscape on a typical day (Sun, vegetation, soil, rocks, encounter in the landscape on a typical day (Sun, vegetation, soil, rocks, water, and even people) water, and even people) emitemit thermal infrared electromagnetic radiation. thermal infrared electromagnetic radiation. Humans sense thermal energy primarily through the sense of touch. Our Humans sense thermal energy primarily through the sense of touch. Our eyes cannot detect differences in thermal infrared energy because they are eyes cannot detect differences in thermal infrared energy because they are primarily sensitive to short wavelength visible light from 0.4 primarily sensitive to short wavelength visible light from 0.4 m to 0.7 m to 0.7 m. Our eyes are not sensitive to the m. Our eyes are not sensitive to the reflective infrared (0.7 - 3.0 reflective infrared (0.7 - 3.0 m) m) or or thermal infrared energy (3.0 - 14 thermal infrared energy (3.0 - 14 m)m). Fortunately, engineers have . Fortunately, engineers have developed developed detectorsdetectors that are sensitive to thermal infrared radiation. These that are sensitive to thermal infrared radiation. These thermal infrared sensors allow humans to sense a previously thermal infrared sensors allow humans to sense a previously invisible invisible world of information world of information as they monitor the as they monitor the thermal characteristics of the thermal characteristics of the landscape.landscape.

Atmospheric Windows in the Electromagnetic SpectrumAtmospheric Windows in the Electromagnetic Spectrum

Fundamental Properties of Fundamental Properties of Electromagnetic RadiationElectromagnetic Radiation

Fundamental Properties of Fundamental Properties of Electromagnetic RadiationElectromagnetic Radiation

The three basic ways in which energy can be transferred:The three basic ways in which energy can be transferred:

• • ConductionConduction occurs when one body (molecule or atom) transfers its occurs when one body (molecule or atom) transfers its kinetic energy to another by colliding with it. This is how a pan is heated kinetic energy to another by colliding with it. This is how a pan is heated on a stove. on a stove.

• • In In convectionconvection, the kinetic energy of bodies is transferred from one place , the kinetic energy of bodies is transferred from one place to another by physically moving the bodies. An example is the to another by physically moving the bodies. An example is the convectional heating of air in the atmosphere in the early afternoon. convectional heating of air in the atmosphere in the early afternoon.

• • The transfer of energy by The transfer of energy by electromagnetic radiationelectromagnetic radiation is of primary interest is of primary interest to remote sensing because it is the only form of energy transfer that can to remote sensing because it is the only form of energy transfer that can take place in a vacuum such as the region between the Sun and the Earth.take place in a vacuum such as the region between the Sun and the Earth.

The three basic ways in which energy can be transferred:The three basic ways in which energy can be transferred:

• • ConductionConduction occurs when one body (molecule or atom) transfers its occurs when one body (molecule or atom) transfers its kinetic energy to another by colliding with it. This is how a pan is heated kinetic energy to another by colliding with it. This is how a pan is heated on a stove. on a stove.

• • In In convectionconvection, the kinetic energy of bodies is transferred from one place , the kinetic energy of bodies is transferred from one place to another by physically moving the bodies. An example is the to another by physically moving the bodies. An example is the convectional heating of air in the atmosphere in the early afternoon. convectional heating of air in the atmosphere in the early afternoon.

• • The transfer of energy by The transfer of energy by electromagnetic radiationelectromagnetic radiation is of primary interest is of primary interest to remote sensing because it is the only form of energy transfer that can to remote sensing because it is the only form of energy transfer that can take place in a vacuum such as the region between the Sun and the Earth.take place in a vacuum such as the region between the Sun and the Earth.

Methods of Heat TransferMethods of Heat Transfer

Pan in contact

with burner

TerrainPulse of

warmair

λConductionConvectionRadiationa. b. c. EarthSunElectromagneticwave

Pan in contact

with burner

TerrainPulse of

warmair

λConductionConvectionRadiationa. b. c. EarthSunElectromagneticwave

History of Thermal Infrared Remote SensingHistory of Thermal Infrared Remote SensingHistory of Thermal Infrared Remote SensingHistory of Thermal Infrared Remote Sensing

•• The astronomer The astronomer Sir Frederick William Herschel Sir Frederick William Herschel (1738-1822) discovered (1738-1822) discovered the infrared portion of the electromagnetic spectrum in 1800 described in the infrared portion of the electromagnetic spectrum in 1800 described in his famous paper “Investigations of the Powers of the Prismatic Colours his famous paper “Investigations of the Powers of the Prismatic Colours to Heat and Illuminate Objects: with Remarks.”to Heat and Illuminate Objects: with Remarks.”

•• In 1879, In 1879, S. P. Langley S. P. Langley began a research program to find a superior began a research program to find a superior radiation detector. One year later he invented the bolometer that was able radiation detector. One year later he invented the bolometer that was able to obtain measurable temperature variations of 1/10,000 ˚C. to obtain measurable temperature variations of 1/10,000 ˚C.

•• In World War I, In World War I, S. O. Hoffman S. O. Hoffman could detect men at 120 m and aircraft. could detect men at 120 m and aircraft.

•• In the 1930s, Germany developed the In the 1930s, Germany developed the Kiel system Kiel system for discriminating for discriminating between bombers and night fighters. between bombers and night fighters.

•• The astronomer The astronomer Sir Frederick William Herschel Sir Frederick William Herschel (1738-1822) discovered (1738-1822) discovered the infrared portion of the electromagnetic spectrum in 1800 described in the infrared portion of the electromagnetic spectrum in 1800 described in his famous paper “Investigations of the Powers of the Prismatic Colours his famous paper “Investigations of the Powers of the Prismatic Colours to Heat and Illuminate Objects: with Remarks.”to Heat and Illuminate Objects: with Remarks.”

•• In 1879, In 1879, S. P. Langley S. P. Langley began a research program to find a superior began a research program to find a superior radiation detector. One year later he invented the bolometer that was able radiation detector. One year later he invented the bolometer that was able to obtain measurable temperature variations of 1/10,000 ˚C. to obtain measurable temperature variations of 1/10,000 ˚C.

•• In World War I, In World War I, S. O. Hoffman S. O. Hoffman could detect men at 120 m and aircraft. could detect men at 120 m and aircraft.

•• In the 1930s, Germany developed the In the 1930s, Germany developed the Kiel system Kiel system for discriminating for discriminating between bombers and night fighters. between bombers and night fighters.


• • The single most important development in infrared technology was The single most important development in infrared technology was the development of the the development of the detector element detector element by nations at war during by nations at war during World War II. Early infrared detectors were World War II. Early infrared detectors were lead salt photodetectorslead salt photodetectors. .

• • Now we have very fast detectors consisting of Now we have very fast detectors consisting of mercury-doped mercury-doped germanium germanium (Ge:Hg), (Ge:Hg), indium antimonide indium antimonide (InSb) and other substances (InSb) and other substances that are very responsive to infrared radiation. We also have computers that are very responsive to infrared radiation. We also have computers to rapidly process and display the thermal radiometric measurements.to rapidly process and display the thermal radiometric measurements.

• • In 1968, the government In 1968, the government declassifieddeclassified thermal infrared remote sensing thermal infrared remote sensing systems that did not exceed a certain spatial resolution and temperature systems that did not exceed a certain spatial resolution and temperature sensitivity.sensitivity.

• • The single most important development in infrared technology was The single most important development in infrared technology was the development of the the development of the detector element detector element by nations at war during by nations at war during World War II. Early infrared detectors were World War II. Early infrared detectors were lead salt photodetectorslead salt photodetectors. .

• • Now we have very fast detectors consisting of Now we have very fast detectors consisting of mercury-doped mercury-doped germanium germanium (Ge:Hg), (Ge:Hg), indium antimonide indium antimonide (InSb) and other substances (InSb) and other substances that are very responsive to infrared radiation. We also have computers that are very responsive to infrared radiation. We also have computers to rapidly process and display the thermal radiometric measurements.to rapidly process and display the thermal radiometric measurements.

• • In 1968, the government In 1968, the government declassifieddeclassified thermal infrared remote sensing thermal infrared remote sensing systems that did not exceed a certain spatial resolution and temperature systems that did not exceed a certain spatial resolution and temperature sensitivity.sensitivity.


• • The first declassified satellite remote sensor data were collected by the The first declassified satellite remote sensor data were collected by the U. S. Television IR Operational Satellite U. S. Television IR Operational Satellite ((TIROSTIROS) launched in 1960. The ) launched in 1960. The coarse resolution thermal infrared data were ideal for monitoring regional coarse resolution thermal infrared data were ideal for monitoring regional cloud patterns and frontal movement. cloud patterns and frontal movement.

• • NASA launched the NASA launched the Heat Capacity Mapping Mission Heat Capacity Mapping Mission ((HCCMHCCM) on April ) on April 26, 1978 that obtained 600 x 600 m spatial resolution thermal infrared 26, 1978 that obtained 600 x 600 m spatial resolution thermal infrared data (10.5 - 12.6 data (10.5 - 12.6 m) both day (1:30 pm) and night (2:30 am). This was m) both day (1:30 pm) and night (2:30 am). This was one of the first scientifically oriented (geology) thermal infrared systems. one of the first scientifically oriented (geology) thermal infrared systems.

• • NASA’s Nimbus 7 launched on October 23, 1978 had a NASA’s Nimbus 7 launched on October 23, 1978 had a Coastal Zone Coastal Zone Color Scanner Color Scanner ((CZCSCZCS) that included a thermal infrared sensor for ) that included a thermal infrared sensor for monitoring sea-surface temperature. monitoring sea-surface temperature.

• • The first declassified satellite remote sensor data were collected by the The first declassified satellite remote sensor data were collected by the U. S. Television IR Operational Satellite U. S. Television IR Operational Satellite ((TIROSTIROS) launched in 1960. The ) launched in 1960. The coarse resolution thermal infrared data were ideal for monitoring regional coarse resolution thermal infrared data were ideal for monitoring regional cloud patterns and frontal movement. cloud patterns and frontal movement.

• • NASA launched the NASA launched the Heat Capacity Mapping Mission Heat Capacity Mapping Mission ((HCCMHCCM) on April ) on April 26, 1978 that obtained 600 x 600 m spatial resolution thermal infrared 26, 1978 that obtained 600 x 600 m spatial resolution thermal infrared data (10.5 - 12.6 data (10.5 - 12.6 m) both day (1:30 pm) and night (2:30 am). This was m) both day (1:30 pm) and night (2:30 am). This was one of the first scientifically oriented (geology) thermal infrared systems. one of the first scientifically oriented (geology) thermal infrared systems.

• • NASA’s Nimbus 7 launched on October 23, 1978 had a NASA’s Nimbus 7 launched on October 23, 1978 had a Coastal Zone Coastal Zone Color Scanner Color Scanner ((CZCSCZCS) that included a thermal infrared sensor for ) that included a thermal infrared sensor for monitoring sea-surface temperature. monitoring sea-surface temperature.


• • In 1980, NASA and the Jet Propulsion Laboratory developed the In 1980, NASA and the Jet Propulsion Laboratory developed the thermal infrared multispectral scanner thermal infrared multispectral scanner ((TIMSTIMS) that acquires thermal ) that acquires thermal infrared energy in six bands at wavelength intervals of <1.0 infrared energy in six bands at wavelength intervals of <1.0 m. m.

•• Landsat Thematic Mapper 4 and 5 Landsat Thematic Mapper 4 and 5 sensors were launched on July 16, sensors were launched on July 16, 1982 and March 1, 1984, respectively, and collected 120 x 120 m 1982 and March 1, 1984, respectively, and collected 120 x 120 m thermal infrared data (10.4 - 12.5 thermal infrared data (10.4 - 12.5 m) along with two bands of middle m) along with two bands of middle infrared data. infrared data.

• • Today, the Today, the NOAA Geostationary Operational Environmental Satellite NOAA Geostationary Operational Environmental Satellite ((GOESGOES) collects thermal infrared data at a spatial resolution of 8 x 8 ) collects thermal infrared data at a spatial resolution of 8 x 8 km for weather prediction. Full-disk images of the earth are obtained km for weather prediction. Full-disk images of the earth are obtained every 30 minutes both day and night by the thermal infrared sensor.every 30 minutes both day and night by the thermal infrared sensor.

• • In 1980, NASA and the Jet Propulsion Laboratory developed the In 1980, NASA and the Jet Propulsion Laboratory developed the thermal infrared multispectral scanner thermal infrared multispectral scanner ((TIMSTIMS) that acquires thermal ) that acquires thermal infrared energy in six bands at wavelength intervals of <1.0 infrared energy in six bands at wavelength intervals of <1.0 m. m.

•• Landsat Thematic Mapper 4 and 5 Landsat Thematic Mapper 4 and 5 sensors were launched on July 16, sensors were launched on July 16, 1982 and March 1, 1984, respectively, and collected 120 x 120 m 1982 and March 1, 1984, respectively, and collected 120 x 120 m thermal infrared data (10.4 - 12.5 thermal infrared data (10.4 - 12.5 m) along with two bands of middle m) along with two bands of middle infrared data. infrared data.

• • Today, the Today, the NOAA Geostationary Operational Environmental Satellite NOAA Geostationary Operational Environmental Satellite ((GOESGOES) collects thermal infrared data at a spatial resolution of 8 x 8 ) collects thermal infrared data at a spatial resolution of 8 x 8 km for weather prediction. Full-disk images of the earth are obtained km for weather prediction. Full-disk images of the earth are obtained every 30 minutes both day and night by the thermal infrared sensor.every 30 minutes both day and night by the thermal infrared sensor.


• • The The NOAA Advanced Very High Resolution Radiometer NOAA Advanced Very High Resolution Radiometer ((AVHRRAVHRR) collects thermal infrared local area coverage (LAC) ) collects thermal infrared local area coverage (LAC) data at 1.1 x 1.1 km and global area coverage (GAC) at 4 x 4 data at 1.1 x 1.1 km and global area coverage (GAC) at 4 x 4 km. The routine collection of thermal infrared data are a part km. The routine collection of thermal infrared data are a part of each person’s daily life as we watch the nightly weather of each person’s daily life as we watch the nightly weather report. report.

• • The The NOAA Advanced Very High Resolution Radiometer NOAA Advanced Very High Resolution Radiometer ((AVHRRAVHRR) collects thermal infrared local area coverage (LAC) ) collects thermal infrared local area coverage (LAC) data at 1.1 x 1.1 km and global area coverage (GAC) at 4 x 4 data at 1.1 x 1.1 km and global area coverage (GAC) at 4 x 4 km. The routine collection of thermal infrared data are a part km. The routine collection of thermal infrared data are a part of each person’s daily life as we watch the nightly weather of each person’s daily life as we watch the nightly weather report. report.

Thermal Infrared Radiation PrinciplesThermal Infrared Radiation PrinciplesThermal Infrared Radiation PrinciplesThermal Infrared Radiation Principles

• • An analyst An analyst cannot interpret a thermal infrared image as if it were an cannot interpret a thermal infrared image as if it were an aerial photograph aerial photograph or a normal image produced by a multispectral or a normal image produced by a multispectral scanner or charge-coupled device. scanner or charge-coupled device.

• • Rather, the image analyst must Rather, the image analyst must thinkthink thermallythermally. .

• • The analyst must understand how energy from the Sun or from the The analyst must understand how energy from the Sun or from the Earth Earth interactsinteracts with the various terrain components and how the with the various terrain components and how the detectors function as they record the terrain’s detectors function as they record the terrain’s emittedemitted thermal infrared thermal infrared electromagnetic radiation. Finally, the analyst must understand how electromagnetic radiation. Finally, the analyst must understand how both the sensor system itself and the terrain can introduce both the sensor system itself and the terrain can introduce noisenoise into into the thermal infrared image that might make the data less useful or lead the thermal infrared image that might make the data less useful or lead to incorrect image interpretation.to incorrect image interpretation.

• • An analyst An analyst cannot interpret a thermal infrared image as if it were an cannot interpret a thermal infrared image as if it were an aerial photograph aerial photograph or a normal image produced by a multispectral or a normal image produced by a multispectral scanner or charge-coupled device. scanner or charge-coupled device.

• • Rather, the image analyst must Rather, the image analyst must thinkthink thermallythermally. .

• • The analyst must understand how energy from the Sun or from the The analyst must understand how energy from the Sun or from the Earth Earth interactsinteracts with the various terrain components and how the with the various terrain components and how the detectors function as they record the terrain’s detectors function as they record the terrain’s emittedemitted thermal infrared thermal infrared electromagnetic radiation. Finally, the analyst must understand how electromagnetic radiation. Finally, the analyst must understand how both the sensor system itself and the terrain can introduce both the sensor system itself and the terrain can introduce noisenoise into into the thermal infrared image that might make the data less useful or lead the thermal infrared image that might make the data less useful or lead to incorrect image interpretation.to incorrect image interpretation.

Characteristics of a Thermal Infrared Airborne Across-

track Scanner

Characteristics of a Thermal Infrared Airborne Across-

track Scanner

Pre-dawn Thermal Infrared Image of Effluent Entering the Savannah River Swamp SystemPre-dawn Thermal Infrared Image of Effluent Entering the Savannah River Swamp System

March 31, 19814:28 am; 3 x 3 m

March 31, 19814:28 am; 3 x 3 m

2x reduction2x reduction

Savannah River Savannah

River

Pre-dawn Thermal Infrared Image of a Pre-dawn Thermal Infrared Image of a Residential Subdivision in Forth Worth, TexasResidential Subdivision in Forth Worth, Texas

Pre-dawn Thermal Infrared Image of a Pre-dawn Thermal Infrared Image of a Residential Subdivision in Forth Worth, TexasResidential Subdivision in Forth Worth, Texas

abcdefhgabcdefhg 250 m AGL1 mrad IFOV

6:45 amJan 10, 19800.25 x 0.25 m

250 m AGL1 mrad IFOV

6:45 amJan 10, 19800.25 x 0.25 m

Kinetic Heat, Temperature, Radiant Kinetic Heat, Temperature, Radiant Energy and Radiant FluxEnergy and Radiant Flux


•• The The energy of particles of matter in random motion energy of particles of matter in random motion is called is called kinetic heat kinetic heat (also referred to as internal, real, or true heat). All objects having a (also referred to as internal, real, or true heat). All objects having a temperature above absolute zero (0 ˚K; -273.16 ˚C; and -459.69 ˚F) temperature above absolute zero (0 ˚K; -273.16 ˚C; and -459.69 ˚F) exhibit this random motion. When these particles collide they change exhibit this random motion. When these particles collide they change their energy state and emit electromagnetic radiation as previously their energy state and emit electromagnetic radiation as previously discussed. discussed.

•• The The amount of heat amount of heat can be measured in can be measured in caloriescalories (the amount of heat (the amount of heat required to raise the temperature of 1 g of water 1 ˚C). We can measure required to raise the temperature of 1 g of water 1 ˚C). We can measure the the true kinetic temperature true kinetic temperature ((TTkinkin) or concentration of this heat using a ) or concentration of this heat using a

thermometerthermometer. We perform this . We perform this in situ in situ (in place) temperature measurement (in place) temperature measurement when we are ill. We can also measure the true kinetic internal temperature when we are ill. We can also measure the true kinetic internal temperature of soil or water by physically touching them with a thermometer.of soil or water by physically touching them with a thermometer.

•• The The energy of particles of matter in random motion energy of particles of matter in random motion is called is called kinetic heat kinetic heat (also referred to as internal, real, or true heat). All objects having a (also referred to as internal, real, or true heat). All objects having a temperature above absolute zero (0 ˚K; -273.16 ˚C; and -459.69 ˚F) temperature above absolute zero (0 ˚K; -273.16 ˚C; and -459.69 ˚F) exhibit this random motion. When these particles collide they change exhibit this random motion. When these particles collide they change their energy state and emit electromagnetic radiation as previously their energy state and emit electromagnetic radiation as previously discussed. discussed.

•• The The amount of heat amount of heat can be measured in can be measured in caloriescalories (the amount of heat (the amount of heat required to raise the temperature of 1 g of water 1 ˚C). We can measure required to raise the temperature of 1 g of water 1 ˚C). We can measure the the true kinetic temperature true kinetic temperature ((TTkinkin) or concentration of this heat using a ) or concentration of this heat using a

thermometerthermometer. We perform this . We perform this in situ in situ (in place) temperature measurement (in place) temperature measurement when we are ill. We can also measure the true kinetic internal temperature when we are ill. We can also measure the true kinetic internal temperature of soil or water by physically touching them with a thermometer.of soil or water by physically touching them with a thermometer.



•• Fortunately for us, an object’s Fortunately for us, an object’s internal kinetic heat internal kinetic heat is also converted to is also converted to radiant energy radiant energy (often called external or apparent energy). The (often called external or apparent energy). The electromagnetic radiation exiting an object is called electromagnetic radiation exiting an object is called radiant fluxradiant flux (() ) and is measured in watts. The concentration of the amount of radiant and is measured in watts. The concentration of the amount of radiant flux flux exitingexiting ( (emittedemitted from) an object is its from) an object is its radiant temperature radiant temperature ((TTradrad). ).

•• There is usually a There is usually a high positive correlation high positive correlation between the true kinetic between the true kinetic temperature of an object (temperature of an object (TTkinkin) and the amount of radiant flux radiated ) and the amount of radiant flux radiated

from the object (from the object (TTradrad). Therefore, we can utilize radiometers placed some ). Therefore, we can utilize radiometers placed some

distance from the object to measure its radiant temperature which distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. hopefully correlates well with the object’s true kinetic temperature. ThisThis is the basis of thermal infrared remote sensingis the basis of thermal infrared remote sensing. .

•• Fortunately for us, an object’s Fortunately for us, an object’s internal kinetic heat internal kinetic heat is also converted to is also converted to radiant energy radiant energy (often called external or apparent energy). The (often called external or apparent energy). The electromagnetic radiation exiting an object is called electromagnetic radiation exiting an object is called radiant fluxradiant flux (() ) and is measured in watts. The concentration of the amount of radiant and is measured in watts. The concentration of the amount of radiant flux flux exitingexiting ( (emittedemitted from) an object is its from) an object is its radiant temperature radiant temperature ((TTradrad). ).

•• There is usually a There is usually a high positive correlation high positive correlation between the true kinetic between the true kinetic temperature of an object (temperature of an object (TTkinkin) and the amount of radiant flux radiated ) and the amount of radiant flux radiated

from the object (from the object (TTradrad). Therefore, we can utilize radiometers placed some ). Therefore, we can utilize radiometers placed some

distance from the object to measure its radiant temperature which distance from the object to measure its radiant temperature which hopefully correlates well with the object’s true kinetic temperature. hopefully correlates well with the object’s true kinetic temperature. ThisThis is the basis of thermal infrared remote sensingis the basis of thermal infrared remote sensing. .

Kinetic Heat, Temperature, Kinetic Heat, Temperature, Radiant Energy and Radiant FluxRadiant Energy and Radiant Flux

Kinetic Heat, Temperature, Kinetic Heat, Temperature, Radiant Energy and Radiant FluxRadiant Energy and Radiant Flux

Unfortunately, the relationship is Unfortunately, the relationship is notnot perfectperfect, with the remote , with the remote measurement of themeasurement of the radiant temperature always being slightly radiant temperature always being slightly less than the true kinetic temperature of the objectless than the true kinetic temperature of the object. This is due . This is due to a thermal property called to a thermal property called emissivityemissivity..

Unfortunately, the relationship is Unfortunately, the relationship is notnot perfectperfect, with the remote , with the remote measurement of themeasurement of the radiant temperature always being slightly radiant temperature always being slightly less than the true kinetic temperature of the objectless than the true kinetic temperature of the object. This is due . This is due to a thermal property called to a thermal property called emissivityemissivity..

Thermal Infrared Atmospheric WindowsThermal Infrared Atmospheric WindowsThermal Infrared Atmospheric WindowsThermal Infrared Atmospheric Windows

•• Beyond the visible region of the electromagnetic spectrum, we Beyond the visible region of the electromagnetic spectrum, we encounter the encounter the reflective infrared region reflective infrared region from from 0.7 - 3.0 0.7 - 3.0 m m and the and the thermal infrared regionthermal infrared region from from 3 - 14 3 - 14 mm. .

•• The only reason we can use remote sensing devices to detect infrared The only reason we can use remote sensing devices to detect infrared energy in these regions is because the atmosphere allows a portion of energy in these regions is because the atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called Regions that pass energy are called atmospheric windowsatmospheric windows. Regions . Regions that absorb most of the infrared energy are called that absorb most of the infrared energy are called absorption bandsabsorption bands. . Water vapor (HWater vapor (H22O), carbon dioxide (COO), carbon dioxide (CO22), and ozone (O), and ozone (O33) are ) are

responsible for most of the absorption. For example, atmospheric water responsible for most of the absorption. For example, atmospheric water vapor (Hvapor (H22O) absorbs most of the energy exiting the terrain in the O) absorbs most of the energy exiting the terrain in the

region from 5 to 7 region from 5 to 7 m making it almost useless for remote sensing.m making it almost useless for remote sensing.

•• Beyond the visible region of the electromagnetic spectrum, we Beyond the visible region of the electromagnetic spectrum, we encounter the encounter the reflective infrared region reflective infrared region from from 0.7 - 3.0 0.7 - 3.0 m m and the and the thermal infrared regionthermal infrared region from from 3 - 14 3 - 14 mm. .

•• The only reason we can use remote sensing devices to detect infrared The only reason we can use remote sensing devices to detect infrared energy in these regions is because the atmosphere allows a portion of energy in these regions is because the atmosphere allows a portion of the infrared energy to be transmitted from the terrain to the detectors. the infrared energy to be transmitted from the terrain to the detectors. Regions that pass energy are called Regions that pass energy are called atmospheric windowsatmospheric windows. Regions . Regions that absorb most of the infrared energy are called that absorb most of the infrared energy are called absorption bandsabsorption bands. . Water vapor (HWater vapor (H22O), carbon dioxide (COO), carbon dioxide (CO22), and ozone (O), and ozone (O33) are ) are

responsible for most of the absorption. For example, atmospheric water responsible for most of the absorption. For example, atmospheric water vapor (Hvapor (H22O) absorbs most of the energy exiting the terrain in the O) absorbs most of the energy exiting the terrain in the

region from 5 to 7 region from 5 to 7 m making it almost useless for remote sensing.m making it almost useless for remote sensing.

Atmospheric Windows in the Electromagnetic SpectrumAtmospheric Windows in the Electromagnetic SpectrumAtmospheric Windows in the Electromagnetic SpectrumAtmospheric Windows in the Electromagnetic Spectrum

Reflective Infrared DetectorsReflective Infrared DetectorsReflective Infrared DetectorsReflective Infrared Detectors

•• Remote sensors can be engineered to be sensitive to the infrared Remote sensors can be engineered to be sensitive to the infrared energy present within the energy present within the reflective infrared reflective infrared atmospheric windows. atmospheric windows.

•• FilmFilm emulsions emulsions can be made sensitive to reflected infrared energy in can be made sensitive to reflected infrared energy in the window fromthe window from 0.7 -.09 0.7 -.09 mm. For example, Kodak’s 2443 color . For example, Kodak’s 2443 color infrared film works within this photographic infrared region and is ideal infrared film works within this photographic infrared region and is ideal for monitoring vegetation and water. for monitoring vegetation and water.

•• Electro-optical detectors on Electro-optical detectors on Landsat Thematic Mapper 4 and 5 Landsat Thematic Mapper 4 and 5 are are sensitive to the reflective infrared windows from sensitive to the reflective infrared windows from 1.55 - 1.75 1.55 - 1.75 m m (TM (TM band 5) and band 5) and 2.08 - 2.35 2.08 - 2.35 m m (TM band 7).(TM band 7).

•• Remote sensors can be engineered to be sensitive to the infrared Remote sensors can be engineered to be sensitive to the infrared energy present within the energy present within the reflective infrared reflective infrared atmospheric windows. atmospheric windows.

•• FilmFilm emulsions emulsions can be made sensitive to reflected infrared energy in can be made sensitive to reflected infrared energy in the window fromthe window from 0.7 -.09 0.7 -.09 mm. For example, Kodak’s 2443 color . For example, Kodak’s 2443 color infrared film works within this photographic infrared region and is ideal infrared film works within this photographic infrared region and is ideal for monitoring vegetation and water. for monitoring vegetation and water.

•• Electro-optical detectors on Electro-optical detectors on Landsat Thematic Mapper 4 and 5 Landsat Thematic Mapper 4 and 5 are are sensitive to the reflective infrared windows from sensitive to the reflective infrared windows from 1.55 - 1.75 1.55 - 1.75 m m (TM (TM band 5) and band 5) and 2.08 - 2.35 2.08 - 2.35 m m (TM band 7).(TM band 7).

Thermal Infrared DetectorsThermal Infrared DetectorsThermal Infrared DetectorsThermal Infrared Detectors

•• Electronic detectors Electronic detectors can also be made sensitive to photons of can also be made sensitive to photons of thermal thermal infrared radiant energyinfrared radiant energy exiting the terrain in the two primary thermal exiting the terrain in the two primary thermal infrared windows: infrared windows: 3 - 5 3 - 5 m m and and 8 - 14 8 - 14 mm. Sub-orbital thermal infrared . Sub-orbital thermal infrared remote sensing systems utilize these spectral bands. remote sensing systems utilize these spectral bands.

•• The Earth’s ozone (OThe Earth’s ozone (O33) layer absorbs much of the thermal energy ) layer absorbs much of the thermal energy

exiting the terrain in an absorption band from approximately 9 - 10 exiting the terrain in an absorption band from approximately 9 - 10 m. m. Therefore, Therefore, satellite thermal infrared remote sensing systems satellite thermal infrared remote sensing systems usually usually only record data in the region from only record data in the region from 10.5 - 12.5 10.5 - 12.5 m m to avoid the to avoid the absorption band.absorption band.

•• Electronic detectors Electronic detectors can also be made sensitive to photons of can also be made sensitive to photons of thermal thermal infrared radiant energyinfrared radiant energy exiting the terrain in the two primary thermal exiting the terrain in the two primary thermal infrared windows: infrared windows: 3 - 5 3 - 5 m m and and 8 - 14 8 - 14 mm. Sub-orbital thermal infrared . Sub-orbital thermal infrared remote sensing systems utilize these spectral bands. remote sensing systems utilize these spectral bands.

•• The Earth’s ozone (OThe Earth’s ozone (O33) layer absorbs much of the thermal energy ) layer absorbs much of the thermal energy

exiting the terrain in an absorption band from approximately 9 - 10 exiting the terrain in an absorption band from approximately 9 - 10 m. m. Therefore, Therefore, satellite thermal infrared remote sensing systems satellite thermal infrared remote sensing systems usually usually only record data in the region from only record data in the region from 10.5 - 12.5 10.5 - 12.5 m m to avoid the to avoid the absorption band.absorption band.

Daytime Optical and Daytime Optical and Nighttime Thermal Nighttime Thermal

Infrared Imagery of the Infrared Imagery of the University of South University of South Carolina CampusCarolina Campus

Daytime Optical and Daytime Optical and Nighttime Thermal Nighttime Thermal

Infrared Imagery of the Infrared Imagery of the University of South University of South Carolina CampusCarolina Campus

AprilApril 26, 19814:56 am 1 x 1 m


2x reduction

a. b. steamlinessteamplantmanhole

coverlibraryparking soccer fielddormsone-dimensional

reliefdisplacement

Vertical Aerial Photograph Pre-dawn Thermal Infrared Image line-of-flightsciencebuildings



reliefdisplacement


Thermal Radiation LawsThermal Radiation LawsThermal Radiation LawsThermal Radiation Laws

•• A A blackbodyblackbody is a theoretical construct that absorbs all the radiant is a theoretical construct that absorbs all the radiant energy striking it and radiates energy at the maximum possible rate per energy striking it and radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. unit area at each wavelength for any given temperature.

• • No objects in nature are true blackbodiesNo objects in nature are true blackbodies, however, we may think of , however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody.˚K blackbody. If we pointed a sensor at a blackbody we would be able If we pointed a sensor at a blackbody we would be able to record quantitative information about the total amount of radiant to record quantitative information about the total amount of radiant energy in specific wavelengths exiting the object and the dominant energy in specific wavelengths exiting the object and the dominant wavelength of the object. wavelength of the object. In order to do this, we utilize two important In order to do this, we utilize two important physical laws: the Stefan-Boltzmann law and Wein’s displacement law. physical laws: the Stefan-Boltzmann law and Wein’s displacement law.

•• A A blackbodyblackbody is a theoretical construct that absorbs all the radiant is a theoretical construct that absorbs all the radiant energy striking it and radiates energy at the maximum possible rate per energy striking it and radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. unit area at each wavelength for any given temperature.

• • No objects in nature are true blackbodiesNo objects in nature are true blackbodies, however, we may think of , however, we may think of the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 the Sun as approximating a 6,000 ˚K blackbody and the Earth as a 300 ˚K blackbody.˚K blackbody. If we pointed a sensor at a blackbody we would be able If we pointed a sensor at a blackbody we would be able to record quantitative information about the total amount of radiant to record quantitative information about the total amount of radiant energy in specific wavelengths exiting the object and the dominant energy in specific wavelengths exiting the object and the dominant wavelength of the object. wavelength of the object. In order to do this, we utilize two important In order to do this, we utilize two important physical laws: the Stefan-Boltzmann law and Wein’s displacement law. physical laws: the Stefan-Boltzmann law and Wein’s displacement law.

The total spectral radiant flux exitance (The total spectral radiant flux exitance (FFbb) measured in watts m) measured in watts m2 2 leaving a leaving a

blackbodyblackbody is proportional to the fourth power of its temperature ( is proportional to the fourth power of its temperature (TT). This ). This is the is the Stefan-Boltzmann law Stefan-Boltzmann law and is expressed as:and is expressed as:

FFbb = = kTkT44

where where kk is the Stefan-Boltzmann constant equaling 2898 mm ˚K, and is the Stefan-Boltzmann constant equaling 2898 mm ˚K, and TT is is temperature in degrees Kelvin.temperature in degrees Kelvin. The total radiant exitance is the integration The total radiant exitance is the integration of all the area under the blackbody radiation curve. of all the area under the blackbody radiation curve.

The Sun produces more spectral radiant exitance (FThe Sun produces more spectral radiant exitance (Fbb) at 6,000 ˚K than the ) at 6,000 ˚K than the

Earth at 300 ˚K. As the temperature increases, the total amount of radiant Earth at 300 ˚K. As the temperature increases, the total amount of radiant energy measured in watts per menergy measured in watts per m22 (the area under the curve) increases and (the area under the curve) increases and the radiant energy peak shifts to shorter wavelengths.the radiant energy peak shifts to shorter wavelengths.

The total spectral radiant flux exitance (The total spectral radiant flux exitance (FFbb) measured in watts m) measured in watts m2 2 leaving a leaving a

blackbodyblackbody is proportional to the fourth power of its temperature ( is proportional to the fourth power of its temperature (TT). This ). This is the is the Stefan-Boltzmann law Stefan-Boltzmann law and is expressed as:and is expressed as:

FFbb = = kTkT44

where where kk is the Stefan-Boltzmann constant equaling 2898 mm ˚K, and is the Stefan-Boltzmann constant equaling 2898 mm ˚K, and TT is is temperature in degrees Kelvin.temperature in degrees Kelvin. The total radiant exitance is the integration The total radiant exitance is the integration of all the area under the blackbody radiation curve. of all the area under the blackbody radiation curve.

The Sun produces more spectral radiant exitance (FThe Sun produces more spectral radiant exitance (Fbb) at 6,000 ˚K than the ) at 6,000 ˚K than the

Earth at 300 ˚K. As the temperature increases, the total amount of radiant Earth at 300 ˚K. As the temperature increases, the total amount of radiant energy measured in watts per menergy measured in watts per m22 (the area under the curve) increases and (the area under the curve) increases and the radiant energy peak shifts to shorter wavelengths.the radiant energy peak shifts to shorter wavelengths.

Stephen Boltzmann LawStephen Boltzmann LawStephen Boltzmann LawStephen Boltzmann Law

Blackbody RadiationRadiation Curves for Several

Objects including the Sun and Earth

Blackbody RadiationRadiation Curves for Several

Objects including the Sun and Earth

The relationship between the true temperature of a blackbody (The relationship between the true temperature of a blackbody (TT) in ) in degrees Kelvin and its degrees Kelvin and its peak spectral exitance peak spectral exitance or or dominant wavelength dominant wavelength ((λλmaxmax) is described by ) is described by Wein’s displacement lawWein’s displacement law: :

λλmaxmax = = kk = = 2898 2898 m ˚Km ˚K

T TT T

where where kk is a constant equaling 2898 is a constant equaling 2898 m ˚K. m ˚K.

The relationship between the true temperature of a blackbody (The relationship between the true temperature of a blackbody (TT) in ) in degrees Kelvin and its degrees Kelvin and its peak spectral exitance peak spectral exitance or or dominant wavelength dominant wavelength ((λλmaxmax) is described by ) is described by Wein’s displacement lawWein’s displacement law: :

λλmaxmax = = kk = = 2898 2898 m ˚Km ˚K

T TT T

where where kk is a constant equaling 2898 is a constant equaling 2898 m ˚K. m ˚K.

Wein’s Displacement LawWein’s Displacement LawWein’s Displacement LawWein’s Displacement Law

For example, the average temperature of the For example, the average temperature of the EarthEarth is 300 ˚K is 300 ˚K (80 ˚F). (80 ˚F).

We compute the We compute the Earth’s dominant wavelength Earth’s dominant wavelength as:as:

λλmaxmax = = 2898 2898 m ˚Km ˚K

TT

λλmaxmax = = 2898 2898 m ˚Km ˚K = = 9.67 9.67 m m

300 ˚K300 ˚K

For example, the average temperature of the For example, the average temperature of the EarthEarth is 300 ˚K is 300 ˚K (80 ˚F). (80 ˚F).

We compute the We compute the Earth’s dominant wavelength Earth’s dominant wavelength as:as:

λλmaxmax = = 2898 2898 m ˚Km ˚K

TT

λλmaxmax = = 2898 2898 m ˚Km ˚K = = 9.67 9.67 m m

300 ˚K300 ˚K


• • The The dominant wavelength dominant wavelength provides valuable information about which provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if part of the thermal spectrum we might want to sense in. For example, if we are looking for we are looking for 800 ˚K forest fires 800 ˚K forest fires that have a dominant wavelength that have a dominant wavelength of approximatelyof approximately 3.62 3.62 m m then the most appropriate remote sensing then the most appropriate remote sensing system might be a system might be a 3-5 3-5 m m thermal infrared detector. thermal infrared detector.

• • If we are interested inIf we are interested in soil, water, and rock with ambient soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K temperatures on the earth’s surface of 300 ˚K and a dominant and a dominant wavelength of wavelength of 9.66 9.66 mm, then a thermal infrared detector operating in , then a thermal infrared detector operating in the the 8 - 14 8 - 14 m m region might be most appropriate.region might be most appropriate.

• • The The dominant wavelength dominant wavelength provides valuable information about which provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if part of the thermal spectrum we might want to sense in. For example, if we are looking for we are looking for 800 ˚K forest fires 800 ˚K forest fires that have a dominant wavelength that have a dominant wavelength of approximatelyof approximately 3.62 3.62 m m then the most appropriate remote sensing then the most appropriate remote sensing system might be a system might be a 3-5 3-5 m m thermal infrared detector. thermal infrared detector.

• • If we are interested inIf we are interested in soil, water, and rock with ambient soil, water, and rock with ambient temperatures on the earth’s surface of 300 ˚K temperatures on the earth’s surface of 300 ˚K and a dominant and a dominant wavelength of wavelength of 9.66 9.66 mm, then a thermal infrared detector operating in , then a thermal infrared detector operating in the the 8 - 14 8 - 14 m m region might be most appropriate.region might be most appropriate.


• • The world is not composed of radiating blackbodies. Rather it is The world is not composed of radiating blackbodies. Rather it is composed of composed of selectively radiating bodies selectively radiating bodies such as rocks, soil, and water such as rocks, soil, and water that emit only a fraction of the energy emitted from a blackbody at the that emit only a fraction of the energy emitted from a blackbody at the same temperature. same temperature. EmissivityEmissivity, , , is the ratio between the radiant flux , is the ratio between the radiant flux exiting a exiting a real-world selective radiating body real-world selective radiating body ((FFrr) and a ) and a blackbody at the blackbody at the

same temperature same temperature ((FFbb):):

FFrr

= ______= ______

FFbb

• • The world is not composed of radiating blackbodies. Rather it is The world is not composed of radiating blackbodies. Rather it is composed of composed of selectively radiating bodies selectively radiating bodies such as rocks, soil, and water such as rocks, soil, and water that emit only a fraction of the energy emitted from a blackbody at the that emit only a fraction of the energy emitted from a blackbody at the same temperature. same temperature. EmissivityEmissivity, , , is the ratio between the radiant flux , is the ratio between the radiant flux exiting a exiting a real-world selective radiating body real-world selective radiating body ((FFrr) and a ) and a blackbody at the blackbody at the

same temperature same temperature ((FFbb):):

FFrr

= ______= ______

FFbb

EmissivityEmissivityEmissivityEmissivity

• All selectively radiating bodies 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 distilled 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 selectively radiating bodies 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 distilled 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.


Spectral emissivity of a Spectral emissivity of a blackbody, a graybody, blackbody, a graybody,

and a hypothetical and a hypothetical selective radiatorselective radiator

Spectral emissivity of a Spectral emissivity of a blackbody, a graybody, blackbody, a graybody,

and a hypothetical and a hypothetical selective radiatorselective radiator

2x reduction2x reduction

Spectral radiant exitance Spectral radiant exitance distribution of the distribution of the

blackbody, graybody, blackbody, graybody, and hypothetical and hypothetical selective radiatorselective radiator

Spectral radiant exitance Spectral radiant exitance distribution of the distribution of the

blackbody, graybody, blackbody, graybody, and hypothetical and hypothetical selective radiatorselective radiator

Spec

tral

Em

issi

vity

, S

pec

tral

Rad

ian

t E

xita

nce

W m

-2 u

m-1

Two rocks lying next to one another on the ground could have the same true kinetic temperature but have different apparent 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, including:

• 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.

• surface roughness -- the greater the surface roughness of an object relative to the size of the incident wavelength, the greater the surface area of the object and potential for absorption and re-emission of energy.

Two rocks lying next to one another on the ground could have the same true kinetic temperature but have different apparent 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, including:

• 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.

• surface roughness -- the greater the surface roughness of an object relative to the size of the incident wavelength, the greater the surface area of the object and potential for absorption and re-emission of 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.

• compaction -- the degree of soil compaction can effect emissivity.

• field-of-view -- the emissivity of a single leaf measured with a very high resolution thermal radiometer will have a different emissivity than an entire tree crown viewed using a coarse spatial resolution radiometer.

• wavelength -- the emissivity of an object is generally considered to be wavelength dependent. For example, while the emissivity of an object is often considered to be constant throughout the 8 - 14 mm region, its emissivity in the 3 -5 mm region may be different.

• 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.

• compaction -- the degree of soil compaction can effect emissivity.

• field-of-view -- the emissivity of a single leaf measured with a very high resolution thermal radiometer will have a different emissivity than an entire tree crown viewed using a coarse spatial resolution radiometer.

• wavelength -- the emissivity of an object is generally considered to be wavelength dependent. For example, while the emissivity of an object is often considered to be constant throughout the 8 - 14 mm region, its emissivity in the 3 -5 mm region may be different.


• viewing angle - the emissivity of an object can vary with sensor viewing angle.

We must take into account an object’s emissivity when we use our remote radiant temperature measurement to measure the object’s true kinetic temperature. This is done by applying Kirchoff’s radiation law.

• viewing angle - the emissivity of an object can vary with sensor viewing angle.

We must take into account an object’s emissivity when we use our remote radiant temperature measurement to measure the object’s true kinetic temperature. This is done by applying Kirchoff’s radiation law.


• Remember that the terrain intercepts incident (incoming) radiant flux (i). This incident energy interacts with terrain materials. The amount of radiant flux reflected from the surface (r), the amount of radiant flux absorbed by the surface (a), and the amount of radiant flux transmitted through the surface (t) can be carefully measured as we apply the principle of conservation of energy and attempt to keep track of what happens to all the incident energy. The general equation for the interaction of spectral (λ) radiant flux with the terrain is:

iλ = rλ + λ + λ

• Remember that the terrain intercepts incident (incoming) radiant flux (i). This incident energy interacts with terrain materials. The amount of radiant flux reflected from the surface (r), the amount of radiant flux absorbed by the surface (a), and the amount of radiant flux transmitted through the surface (t) can be carefully measured as we apply the principle of conservation of energy and attempt to keep track of what happens to all the incident energy. The general equation for the interaction of spectral (λ) radiant flux with the terrain is:

iλ = rλ + λ + λ

Kirchoff’s Radiation LawKirchoff’s Radiation Law

• Dividing each of the variables by the original incident radiant flux:

iλ / iλ = (rλ / iλ) +( λ / iλ) +( λ / iλ)

allows us to rewrite the initial equation as:

= rλ + λ + λ

where rλ is spectral hemispherical reflectance by the terrain, λ is spectral hemispherical absorptance, and λ is spectral hemispherical transmittance.

• Dividing each of the variables by the original incident radiant flux:

iλ / iλ = (rλ / iλ) +( λ / iλ) +( λ / iλ)

allows us to rewrite the initial equation as:

= rλ + λ + λ

where rλ is spectral hemispherical reflectance by the terrain, λ is spectral hemispherical absorptance, and λ is spectral hemispherical transmittance.


• • The The Russian physicist Kirchhoff Russian physicist Kirchhoff found that in the infrared portion of found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e. spectral absorptance, i.e. λλ ~~ λλ. This is often phrased as:. This is often phrased as:

““good absorbers are good emitters and good absorbers are good emitters and

good reflectors are poor emitters”good reflectors are poor emitters”..

Also, most real-world materials are usually opaque to thermal radiation Also, most real-world materials are usually opaque to thermal radiation meaning that no radiant flux exits from the other side of the terrain meaning that no radiant flux exits from the other side of the terrain element. Therefore, we may assume transmittance, element. Therefore, we may assume transmittance, λλ = 0 = 0. Substituting . Substituting

emissivity for absorptance and removing transmittance from the emissivity for absorptance and removing transmittance from the equation yields:equation yields:

= r= rλ λ + + λλ

• • The The Russian physicist Kirchhoff Russian physicist Kirchhoff found that in the infrared portion of found that in the infrared portion of the spectrum the spectral emissivity of an object generally equals its the spectrum the spectral emissivity of an object generally equals its spectral absorptance, i.e. spectral absorptance, i.e. λλ ~~ λλ. This is often phrased as:. This is often phrased as:

““good absorbers are good emitters and good absorbers are good emitters and

good reflectors are poor emitters”good reflectors are poor emitters”..

Also, most real-world materials are usually opaque to thermal radiation Also, most real-world materials are usually opaque to thermal radiation meaning that no radiant flux exits from the other side of the terrain meaning that no radiant flux exits from the other side of the terrain element. Therefore, we may assume transmittance, element. Therefore, we may assume transmittance, λλ = 0 = 0. Substituting . Substituting

emissivity for absorptance and removing transmittance from the emissivity for absorptance and removing transmittance from the equation yields:equation yields:

= r= rλ λ + + λλ

Kirchoff’s Radiation LawKirchoff’s Radiation LawKirchoff’s Radiation LawKirchoff’s Radiation Law

• • This simple relationship describes why objects appear as they do on This simple relationship describes why objects appear as they do on thermal infrared imagery. thermal infrared imagery. Because the terrain does not lose any Because the terrain does not lose any incident energy to transmittance, all of the energy leaving the object incident energy to transmittance, all of the energy leaving the object must be accounted for by the inverse relationship between reflectance must be accounted for by the inverse relationship between reflectance (r(rλλ) and emissivity () and emissivity (λλ). ). If reflectivity increases then emissivity must If reflectivity increases then emissivity must

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

• • This simple relationship describes why objects appear as they do on This simple relationship describes why objects appear as they do on thermal infrared imagery. thermal infrared imagery. Because the terrain does not lose any Because the terrain does not lose any incident energy to transmittance, all of the energy leaving the object incident energy to transmittance, all of the energy leaving the object must be accounted for by the inverse relationship between reflectance must be accounted for by the inverse relationship between reflectance (r(rλλ) and emissivity () and emissivity (λλ). ). If reflectivity increases then emissivity must If reflectivity increases then emissivity must

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


• • The goal of thermal infrared remote sensing is to be able to point a The goal of thermal infrared remote sensing is to be able to point a radiometer at an object and have the apparent radiant temperature radiometer at an object and have the apparent radiant temperature recorded (recorded (TTradrad) equal the true kinetic temperature of the object () equal the true kinetic temperature of the object (TTkinkin). ).

Unfortunately, the radiant flux from a real-world object at a given Unfortunately, the radiant flux from a real-world object at a given temperature is not the same as the radiant flux from a blackbody at the temperature is not the same as the radiant flux from a blackbody at the same temperature largely due to the effects of same temperature largely due to the effects of emissivityemissivity. Knowing the . Knowing the emissivity characteristics of an object makes it possible to modify the emissivity characteristics of an object makes it possible to modify the Stefan-Boltzmann law (originally applicable to blackbodies) so that it Stefan-Boltzmann law (originally applicable to blackbodies) so that it pertains to the total spectral radiant flux of pertains to the total spectral radiant flux of real-world materials real-world materials ((FFrr):):

FFrr = = k Tk Tkin kin 44

It takes into account the It takes into account the temperaturetemperature of the object and its of the object and its emissivityemissivity to to create a more accurate estimate of the radiant flux exiting an object.create a more accurate estimate of the radiant flux exiting an object.

• • The goal of thermal infrared remote sensing is to be able to point a The goal of thermal infrared remote sensing is to be able to point a radiometer at an object and have the apparent radiant temperature radiometer at an object and have the apparent radiant temperature recorded (recorded (TTradrad) equal the true kinetic temperature of the object () equal the true kinetic temperature of the object (TTkinkin). ).

Unfortunately, the radiant flux from a real-world object at a given Unfortunately, the radiant flux from a real-world object at a given temperature is not the same as the radiant flux from a blackbody at the temperature is not the same as the radiant flux from a blackbody at the same temperature largely due to the effects of same temperature largely due to the effects of emissivityemissivity. Knowing the . Knowing the emissivity characteristics of an object makes it possible to modify the emissivity characteristics of an object makes it possible to modify the Stefan-Boltzmann law (originally applicable to blackbodies) so that it Stefan-Boltzmann law (originally applicable to blackbodies) so that it pertains to the total spectral radiant flux of pertains to the total spectral radiant flux of real-world materials real-world materials ((FFrr):):

FFrr = = k Tk Tkin kin 44

It takes into account the It takes into account the temperaturetemperature of the object and its of the object and its emissivityemissivity to to create a more accurate estimate of the radiant flux exiting an object.create a more accurate estimate of the radiant flux exiting an object.


• • Thermal infrared remote sensing systems generally record the Thermal infrared remote sensing systems generally record the apparent radiant temperature, apparent radiant temperature, TTradrad of the terrain rather than the true of the terrain rather than the true

kinetic temperature, kinetic temperature, TTkinkin. If we assume that the incorporation of . If we assume that the incorporation of

emissivity in the previous equation has improved our measurement to emissivity in the previous equation has improved our measurement to the point that: the point that: FFrr = = k Tk Tkin kin

4 4 and we assume that and we assume that

FFb b = = k Tk Tradrad4 4 andand

FFr r = = FFb b then,then,

k Tk Tradrad4 4 = = k Tk Tkin kin

44

Therefore, the radiant temperature of an object recorded by a remote Therefore, the radiant temperature of an object recorded by a remote sensor is related to its true kinetic temperature and emissivity by the sensor is related to its true kinetic temperature and emissivity by the following relationship: following relationship: TTradrad

= = 1/41/4TTkinkin

• • Thermal infrared remote sensing systems generally record the Thermal infrared remote sensing systems generally record the apparent radiant temperature, apparent radiant temperature, TTradrad of the terrain rather than the true of the terrain rather than the true

kinetic temperature, kinetic temperature, TTkinkin. If we assume that the incorporation of . If we assume that the incorporation of

emissivity in the previous equation has improved our measurement to emissivity in the previous equation has improved our measurement to the point that: the point that: FFrr = = k Tk Tkin kin

4 4 and we assume that and we assume that

FFb b = = k Tk Tradrad4 4 andand

FFr r = = FFb b then,then,

k Tk Tradrad4 4 = = k Tk Tkin kin

44

Therefore, the radiant temperature of an object recorded by a remote Therefore, the radiant temperature of an object recorded by a remote sensor is related to its true kinetic temperature and emissivity by the sensor is related to its true kinetic temperature and emissivity by the following relationship: following relationship: TTradrad

= = 1/41/4TTkinkin


• • Water, rocks, soil, vegetation, the atmosphere, and human tissue all Water, rocks, soil, vegetation, the atmosphere, and human tissue all have the ability to conduct heat directly through them (have the ability to conduct heat directly through them (thermal thermal conductivityconductivity) onto another surface and to store heat () onto another surface and to store heat (thermal capacitythermal capacity). ). Some materials respond to changes in temperature more rapidly or Some materials respond to changes in temperature more rapidly or slowly than others (slowly than others (thermal inertiathermal inertia). ).

• • Water, rocks, soil, vegetation, the atmosphere, and human tissue all Water, rocks, soil, vegetation, the atmosphere, and human tissue all have the ability to conduct heat directly through them (have the ability to conduct heat directly through them (thermal thermal conductivityconductivity) onto another surface and to store heat () onto another surface and to store heat (thermal capacitythermal capacity). ). Some materials respond to changes in temperature more rapidly or Some materials respond to changes in temperature more rapidly or slowly than others (slowly than others (thermal inertiathermal inertia). ).

Thermal Properties of TerrainThermal Properties of TerrainThermal Properties of TerrainThermal Properties of Terrain

• • Thermal capacityThermal capacity ((cc) is the ability of a material to store heat. It is ) is the ability of a material to store heat. It is measured as the number of calories required to raise a gram of material measured as the number of calories required to raise a gram of material (e.g. water) 1 ˚C (cal g-1 ˚C-1). Water has the highest thermal capacity (e.g. water) 1 ˚C (cal g-1 ˚C-1). Water has the highest thermal capacity (1.00). It stores heat very well relative to all the other materials.(1.00). It stores heat very well relative to all the other materials.

• • Thermal conductivityThermal conductivity ((KK) is the rate that heat will pass through a ) is the rate that heat will pass through a material and is measured as the number of calories that will pass material and is measured as the number of calories that will pass through a 1-cm cube of material in 1 second when two opposite faces through a 1-cm cube of material in 1 second when two opposite faces are maintained at 1 ˚C difference in temperature (cal cmare maintained at 1 ˚C difference in temperature (cal cm -1 -1 secsec-1 -1 ˚C). The ˚C). The conductivity of a material is variable due to soil moisture and particle conductivity of a material is variable due to soil moisture and particle size. Many rocks and soils are extremely poor conductors of heat.size. Many rocks and soils are extremely poor conductors of heat.

• • Thermal capacityThermal capacity ((cc) is the ability of a material to store heat. It is ) is the ability of a material to store heat. It is measured as the number of calories required to raise a gram of material measured as the number of calories required to raise a gram of material (e.g. water) 1 ˚C (cal g-1 ˚C-1). Water has the highest thermal capacity (e.g. water) 1 ˚C (cal g-1 ˚C-1). Water has the highest thermal capacity (1.00). It stores heat very well relative to all the other materials.(1.00). It stores heat very well relative to all the other materials.

• • Thermal conductivityThermal conductivity ((KK) is the rate that heat will pass through a ) is the rate that heat will pass through a material and is measured as the number of calories that will pass material and is measured as the number of calories that will pass through a 1-cm cube of material in 1 second when two opposite faces through a 1-cm cube of material in 1 second when two opposite faces are maintained at 1 ˚C difference in temperature (cal cmare maintained at 1 ˚C difference in temperature (cal cm -1 -1 secsec-1 -1 ˚C). The ˚C). The conductivity of a material is variable due to soil moisture and particle conductivity of a material is variable due to soil moisture and particle size. Many rocks and soils are extremely poor conductors of heat.size. Many rocks and soils are extremely poor conductors of heat.

Thermal Properties of TerrainThermal Properties of TerrainThermal Properties of TerrainThermal Properties of Terrain

•• Thermal inertiaThermal inertia ((PP) is a measurement of the thermal response of a ) is a measurement of the thermal response of a material to temperature changes and is measured in calories per square material to temperature changes and is measured in calories per square centimeter per second square root per degree Celsius (cal cmcentimeter per second square root per degree Celsius (cal cm -2 -2 sec sec -1/2 -1/2

˚C˚C-1-1). Thermal inertia is computed using the equation:). Thermal inertia is computed using the equation:

P = (K x p x c)P = (K x p x c)1/21/2

where where KK is thermal conductivity, is thermal conductivity, pp is density (g cm is density (g cm-3-3), and ), and cc is thermal is thermal capacity. Density is the most important property in this equation capacity. Density is the most important property in this equation because thermal inertia generally increases linearly with increasing because thermal inertia generally increases linearly with increasing material density. material density.

•• Thermal inertiaThermal inertia ((PP) is a measurement of the thermal response of a ) is a measurement of the thermal response of a material to temperature changes and is measured in calories per square material to temperature changes and is measured in calories per square centimeter per second square root per degree Celsius (cal cmcentimeter per second square root per degree Celsius (cal cm -2 -2 sec sec -1/2 -1/2

˚C˚C-1-1). Thermal inertia is computed using the equation:). Thermal inertia is computed using the equation:

P = (K x p x c)P = (K x p x c)1/21/2

where where KK is thermal conductivity, is thermal conductivity, pp is density (g cm is density (g cm-3-3), and ), and cc is thermal is thermal capacity. Density is the most important property in this equation capacity. Density is the most important property in this equation because thermal inertia generally increases linearly with increasing because thermal inertia generally increases linearly with increasing material density. material density.

Thermal InertiaThermal InertiaThermal InertiaThermal Inertia

•• It would be wonderful if we could remotely sense each of the aforementioned It would be wonderful if we could remotely sense each of the aforementioned variables and then simply compute thermal inertia. Unfortunately, this is not the case variables and then simply compute thermal inertia. Unfortunately, this is not the case because conductivity, density, and thermal capacity must all be measuredbecause conductivity, density, and thermal capacity must all be measured in situ in situ. . Nevertheless, it is possible to remotely sense and compute an Nevertheless, it is possible to remotely sense and compute an apparent thermal inertia apparent thermal inertia measurement per pixel in the following manner. A thermal infrared image is acquired measurement per pixel in the following manner. A thermal infrared image is acquired over the identical terrain in the nighttime and in the early afternoon. The two images over the identical terrain in the nighttime and in the early afternoon. The two images are geometrically and radiometrically registered to one another and the change in are geometrically and radiometrically registered to one another and the change in temperature, temperature, ∆T∆T for a specific pixel is determined by subtracting the nighttime apparent for a specific pixel is determined by subtracting the nighttime apparent temperature from the daytime apparent temperature. The apparent thermal inertia (ATI) temperature from the daytime apparent temperature. The apparent thermal inertia (ATI) per pixel is:per pixel is:

ATI = ATI = 1 - A1 - A

∆ ∆TT

with with AA being the albedo (reflectance) measured in a visible band of the spectrum for the being the albedo (reflectance) measured in a visible band of the spectrum for the pixel of interest.pixel of interest.

•• It would be wonderful if we could remotely sense each of the aforementioned It would be wonderful if we could remotely sense each of the aforementioned variables and then simply compute thermal inertia. Unfortunately, this is not the case variables and then simply compute thermal inertia. Unfortunately, this is not the case because conductivity, density, and thermal capacity must all be measuredbecause conductivity, density, and thermal capacity must all be measured in situ in situ. . Nevertheless, it is possible to remotely sense and compute an Nevertheless, it is possible to remotely sense and compute an apparent thermal inertia apparent thermal inertia measurement per pixel in the following manner. A thermal infrared image is acquired measurement per pixel in the following manner. A thermal infrared image is acquired over the identical terrain in the nighttime and in the early afternoon. The two images over the identical terrain in the nighttime and in the early afternoon. The two images are geometrically and radiometrically registered to one another and the change in are geometrically and radiometrically registered to one another and the change in temperature, temperature, ∆T∆T for a specific pixel is determined by subtracting the nighttime apparent for a specific pixel is determined by subtracting the nighttime apparent temperature from the daytime apparent temperature. The apparent thermal inertia (ATI) temperature from the daytime apparent temperature. The apparent thermal inertia (ATI) per pixel is:per pixel is:

ATI = ATI = 1 - A1 - A

∆ ∆TT

with with AA being the albedo (reflectance) measured in a visible band of the spectrum for the being the albedo (reflectance) measured in a visible band of the spectrum for the pixel of interest.pixel of interest.

Apparent Thermal InertiaApparent Thermal InertiaApparent Thermal InertiaApparent Thermal Inertia

Thermal infrared remote sensor data may be collected by: Thermal infrared remote sensor data may be collected by:

• • across-track thermal scannersacross-track thermal scanners, and, and

• • push-broom linear and area array charge-coupled push-broom linear and area array charge-coupled

device (CCD) detectorsdevice (CCD) detectors..

Thermal infrared remote sensor data may be collected by: Thermal infrared remote sensor data may be collected by:

• • across-track thermal scannersacross-track thermal scanners, and, and

• • push-broom linear and area array charge-coupled push-broom linear and area array charge-coupled

device (CCD) detectorsdevice (CCD) detectors..

Thermal Infrared Data CollectionThermal Infrared Data CollectionThermal Infrared Data CollectionThermal Infrared Data Collection

• Daedalus DS-1260, DS-1268, and Airborne Multispectral Scanner

• These scanners provide most of the useful high spatial and spectral resolution thermal infrared data for monitoring the environment. The DS-1260 records data in 10 bands including a thermal-infrared channel (8.5 to 13.5 µm). The DS-1268 incorporates the thematic mapper middle-infrared bands (1.55 - 1.75 µm and 2.08 - 2.35 µm). The AMS contains a hot-target, thermal-infrared detector (3.0 to 5.5 µm) in addition to the standard thermal-infrared detector (8.5 to 12.5 µm).

• Daedalus DS-1260, DS-1268, and Airborne Multispectral Scanner

• These scanners provide most of the useful high spatial and spectral resolution thermal infrared data for monitoring the environment. The DS-1260 records data in 10 bands including a thermal-infrared channel (8.5 to 13.5 µm). The DS-1268 incorporates the thematic mapper middle-infrared bands (1.55 - 1.75 µm and 2.08 - 2.35 µm). The AMS contains a hot-target, thermal-infrared detector (3.0 to 5.5 µm) in addition to the standard thermal-infrared detector (8.5 to 12.5 µm).

Thermal Infrared Multispectral ScannersThermal Infrared Multispectral Scanners

• • The The diameterdiameter of the circular ground area viewed by the of the circular ground area viewed by the sensor, sensor, DD, is a function of the , is a function of the instantaneous-field-of-viewinstantaneous-field-of-view, , , , of the scanner measured in milliradians (mrad) and the of the scanner measured in milliradians (mrad) and the altitude altitude of the scanner above ground levelof the scanner above ground level, , HH, where:, where:

D = H x D = H x

For example, if the IFOV of the scanner is 2.5 mrad, the 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 ground size of the pixel in meters is a product of the IFOV (0.0025) and the altitude above ground level (AGL) in meters. (0.0025) and the altitude above ground level (AGL) in meters. IFOVs range from 0.5 to 5 milliradiansIFOVs range from 0.5 to 5 milliradians

• • The The diameterdiameter of the circular ground area viewed by the of the circular ground area viewed by the sensor, sensor, DD, is a function of the , is a function of the instantaneous-field-of-viewinstantaneous-field-of-view, , , , of the scanner measured in milliradians (mrad) and the of the scanner measured in milliradians (mrad) and the altitude altitude of the scanner above ground levelof the scanner above ground level, , HH, where:, where:

D = H x D = H x

For example, if the IFOV of the scanner is 2.5 mrad, the 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 ground size of the pixel in meters is a product of the IFOV (0.0025) and the altitude above ground level (AGL) in meters. (0.0025) and the altitude above ground level (AGL) in meters. IFOVs range from 0.5 to 5 milliradiansIFOVs range from 0.5 to 5 milliradians

Thermal Infrared Multispectral ScannersThermal Infrared Multispectral ScannersThermal Infrared Multispectral ScannersThermal Infrared Multispectral Scanners

Characteristics of a Thermal Infrared

Airborne Across-track Scanner

Characteristics of a Thermal Infrared

Airborne Across-track Scanner

Ground Resolution Cell Size Along a Single Across-Track ScanGround Resolution Cell Size Along a Single Across-Track Scan

Thermal infrared detectors are usually composed of:

• In:Sb (indium antimonide) with a peak sensitivity near 5µm;

• Gd:Hg (mercury-doped germanium) with a peak sensitivity near 10 µm, or

• Hg:Cd:Te (mercury-cadmium-telluride) sensitive over the range from 8 - 14 µm.

The detectors are cooled to low temperatures (-196 ˚C; -243 ˚C; 73 ˚K) using liquid helium or liquid nitrogen. Cooling the detectors insures that the radiant energy (photons) recorded by the detectors comes from the terrain and not from the ambient temperature of objects within the scanner itself.

Thermal infrared detectors are usually composed of:

• In:Sb (indium antimonide) with a peak sensitivity near 5µm;

• Gd:Hg (mercury-doped germanium) with a peak sensitivity near 10 µm, or

• Hg:Cd:Te (mercury-cadmium-telluride) sensitive over the range from 8 - 14 µm.

The detectors are cooled to low temperatures (-196 ˚C; -243 ˚C; 73 ˚K) using liquid helium or liquid nitrogen. Cooling the detectors insures that the radiant energy (photons) recorded by the detectors comes from the terrain and not from the ambient temperature of objects within the scanner itself.

Thermal Infrared DetectorsThermal Infrared Detectors

Peak Sensitivity of Indium-Antimonide and Mercury-

doped Germanium Thermal InfraredDetectors

Peak Sensitivity of Indium-Antimonide and Mercury-

doped Germanium Thermal InfraredDetectors

There is an There is an inverse relationship inverse relationship between having between having high spatial resolution high spatial resolution andand high radiometric resolution high radiometric resolution when collecting thermal infrared data. when collecting thermal infrared data.

• • The larger the radiometer instantaneous-field-of-view, The larger the radiometer instantaneous-field-of-view, , the longer the dwell time , the longer the dwell time that an individual detector can view the terrain within the IFOV during a single sweep that an individual detector can view the terrain within the IFOV during a single sweep of the mirror. A larger IFOV provides good radiometric resolution which is the ability of the mirror. A larger IFOV provides good radiometric resolution which is the ability to discriminate between very small differences in radiant energy exiting the terrain to discriminate between very small differences in radiant energy exiting the terrain element. In fact, the radiant energy signal measured may well be much stronger than element. In fact, the radiant energy signal measured may well be much stronger than any noise introduced from the sensor system components. When this takes place we any noise introduced from the sensor system components. When this takes place we say that we have a say that we have a good signal to noise ratiogood signal to noise ratio. Of course, the larger the IFOV, the poorer . Of course, the larger the IFOV, the poorer the ability to resolve fine spatial detail. Selecting a smaller IFOV will increase the the ability to resolve fine spatial detail. Selecting a smaller IFOV will increase the spatial resolution. But, the sensor will dwell a shorter time on each terrain element spatial resolution. But, the sensor will dwell a shorter time on each terrain element during a sweep of the mirror, resulting in poorer radiometric resolution and perhaps a during a sweep of the mirror, resulting in poorer radiometric resolution and perhaps a poorer signal to noise ratio.poorer signal to noise ratio.

There is an There is an inverse relationship inverse relationship between having between having high spatial resolution high spatial resolution andand high radiometric resolution high radiometric resolution when collecting thermal infrared data. when collecting thermal infrared data.

• • The larger the radiometer instantaneous-field-of-view, The larger the radiometer instantaneous-field-of-view, , the longer the dwell time , the longer the dwell time that an individual detector can view the terrain within the IFOV during a single sweep that an individual detector can view the terrain within the IFOV during a single sweep of the mirror. A larger IFOV provides good radiometric resolution which is the ability of the mirror. A larger IFOV provides good radiometric resolution which is the ability to discriminate between very small differences in radiant energy exiting the terrain to discriminate between very small differences in radiant energy exiting the terrain element. In fact, the radiant energy signal measured may well be much stronger than element. In fact, the radiant energy signal measured may well be much stronger than any noise introduced from the sensor system components. When this takes place we any noise introduced from the sensor system components. When this takes place we say that we have a say that we have a good signal to noise ratiogood signal to noise ratio. Of course, the larger the IFOV, the poorer . Of course, the larger the IFOV, the poorer the ability to resolve fine spatial detail. Selecting a smaller IFOV will increase the the ability to resolve fine spatial detail. Selecting a smaller IFOV will increase the spatial resolution. But, the sensor will dwell a shorter time on each terrain element spatial resolution. But, the sensor will dwell a shorter time on each terrain element during a sweep of the mirror, resulting in poorer radiometric resolution and perhaps a during a sweep of the mirror, resulting in poorer radiometric resolution and perhaps a poorer signal to noise ratio.poorer signal to noise ratio.


Halving the distance of a remote sensing detector from a point Halving the distance of a remote sensing detector from a point source quadruples the infrared energy received by that detector. source quadruples the infrared energy received by that detector. The The inverse-square law inverse-square law states that:states that:

““the intensity of radiation emitted from a point source the intensity of radiation emitted from a point source varies as the inverse square of the distance between varies as the inverse square of the distance between source and receiver.” source and receiver.”

Thus, we can obtain a more intense, strong thermal infrared Thus, we can obtain a more intense, strong thermal infrared signal if we can get the remote sensor detector as close to the signal if we can get the remote sensor detector as close to the ground as practical.ground as practical.

Halving the distance of a remote sensing detector from a point Halving the distance of a remote sensing detector from a point source quadruples the infrared energy received by that detector. source quadruples the infrared energy received by that detector. The The inverse-square law inverse-square law states that:states that:

““the intensity of radiation emitted from a point source the intensity of radiation emitted from a point source varies as the inverse square of the distance between varies as the inverse square of the distance between source and receiver.” source and receiver.”

Thus, we can obtain a more intense, strong thermal infrared Thus, we can obtain a more intense, strong thermal infrared signal if we can get the remote sensor detector as close to the signal if we can get the remote sensor detector as close to the ground as practical.ground as practical.

Inverse-Square LawInverse-Square LawInverse-Square LawInverse-Square Law

D2 D1 d 2d Inverse-square Law Blackbody Point Source, S remotedetectors

1 cm2

D2 D1 d 2d Inverse-square Law Blackbody Point Source, S remotedetectors

1 cm2 The intensity of The intensity of

thermal radiation thermal radiation emitted from a point emitted from a point source, source, SS, varies as , varies as

the inverse square of the inverse square of the distance, the distance, dd, ,

between the source between the source and remote detector and remote detector receiver, receiver, DD11 or or DD22

The intensity of The intensity of thermal radiation thermal radiation

emitted from a point emitted from a point source, source, SS, varies as , varies as

the inverse square of the inverse square of the distance, the distance, dd, ,

between the source between the source and remote detector and remote detector receiver, receiver, DD11 or or DD22

Most thermal infrared remote sensing investigations try to maintain good Most thermal infrared remote sensing investigations try to maintain good radiometric and spatial resolution by: radiometric and spatial resolution by:

• • selecting a fairly large IFOV such as 2.5 mrad, and selecting a fairly large IFOV such as 2.5 mrad, and

• • flying at a relatively low altitude to obtain smaller pixel sizes. flying at a relatively low altitude to obtain smaller pixel sizes.

Unfortunately, at lower altitudes, the high spatial resolution may be Unfortunately, at lower altitudes, the high spatial resolution may be outweighed by the fact that outweighed by the fact that more flight lines are required to cover the more flight lines are required to cover the area area compared to more efficient coverage at higher altitudes with larger compared to more efficient coverage at higher altitudes with larger pixels. The pixel size and the geographic size of the survey are pixels. The pixel size and the geographic size of the survey are considered, objectives are weighed, and a compromise is reached. considered, objectives are weighed, and a compromise is reached. Multiple flight lines of aircraft MSS data are difficult to mosaicMultiple flight lines of aircraft MSS data are difficult to mosaic..

Most thermal infrared remote sensing investigations try to maintain good Most thermal infrared remote sensing investigations try to maintain good radiometric and spatial resolution by: radiometric and spatial resolution by:

• • selecting a fairly large IFOV such as 2.5 mrad, and selecting a fairly large IFOV such as 2.5 mrad, and

• • flying at a relatively low altitude to obtain smaller pixel sizes. flying at a relatively low altitude to obtain smaller pixel sizes.

Unfortunately, at lower altitudes, the high spatial resolution may be Unfortunately, at lower altitudes, the high spatial resolution may be outweighed by the fact that outweighed by the fact that more flight lines are required to cover the more flight lines are required to cover the area area compared to more efficient coverage at higher altitudes with larger compared to more efficient coverage at higher altitudes with larger pixels. The pixel size and the geographic size of the survey are pixels. The pixel size and the geographic size of the survey are considered, objectives are weighed, and a compromise is reached. considered, objectives are weighed, and a compromise is reached. Multiple flight lines of aircraft MSS data are difficult to mosaicMultiple flight lines of aircraft MSS data are difficult to mosaic..

ConsiderationConsiderationConsiderationConsideration

Thermal infrared scanning systems (actually all scanning systems) Thermal infrared scanning systems (actually all scanning systems) introduce numerous types ofintroduce numerous types of geometric errorgeometric error that must be understood that must be understood because they impact a) the quality of the imagery for visual or digital because they impact a) the quality of the imagery for visual or digital image processing and analysis, and b) the creation of planimetric maps image processing and analysis, and b) the creation of planimetric maps from the thermal infrared data. The most important considerations are: from the thermal infrared data. The most important considerations are:

• • ground swath width;ground swath width;

• • spatial resolution cell size;spatial resolution cell size;

• • tangential scale distortion, andtangential scale distortion, and

• • one-dimensional relief displacement.one-dimensional relief displacement.

Thermal infrared scanning systems (actually all scanning systems) Thermal infrared scanning systems (actually all scanning systems) introduce numerous types ofintroduce numerous types of geometric errorgeometric error that must be understood that must be understood because they impact a) the quality of the imagery for visual or digital because they impact a) the quality of the imagery for visual or digital image processing and analysis, and b) the creation of planimetric maps image processing and analysis, and b) the creation of planimetric maps from the thermal infrared data. The most important considerations are: from the thermal infrared data. The most important considerations are:

• • ground swath width;ground swath width;

• • spatial resolution cell size;spatial resolution cell size;

• • tangential scale distortion, andtangential scale distortion, and

• • one-dimensional relief displacement.one-dimensional relief displacement.

Geometric Correction of Across-Track Geometric Correction of Across-Track Thermal Infrared Scanner DataThermal Infrared Scanner Data

Geometric Correction of Across-Track Geometric Correction of Across-Track Thermal Infrared Scanner DataThermal Infrared Scanner Data

Perspective Geometry of a Vertical Aerial Photograph Perspective Geometry of a Vertical Aerial Photograph and Across-track One-dimensional Relief Displacementand Across-track One-dimensional Relief Displacement

and Tangential Scale Distortionand Tangential Scale Distortion

Perspective Geometry of a Vertical Aerial Photograph Perspective Geometry of a Vertical Aerial Photograph and Across-track One-dimensional Relief Displacementand Across-track One-dimensional Relief Displacement

and Tangential Scale Distortionand Tangential Scale Distortion

Daytime Optical Daytime Optical and Nighttime and Nighttime

Thermal Infrared Thermal Infrared Imagery of New Imagery of New

York CityYork City

Daytime Optical Daytime Optical and Nighttime and Nighttime

Thermal Infrared Thermal Infrared Imagery of New Imagery of New

York CityYork City

Thermal InfraredThermal InfraredThermal InfraredThermal InfraredAerial PhotographAerial PhotographAerial PhotographAerial Photograph

Daytime Optical and Daytime Optical and Nighttime Thermal Infrared Nighttime Thermal Infrared Imagery of the University of Imagery of the University of

South Carolina CampusSouth Carolina Campus

Daytime Optical and Daytime Optical and Nighttime Thermal Infrared Nighttime Thermal Infrared Imagery of the University of Imagery of the University of

South Carolina CampusSouth Carolina Campus



2x reduction



reliefdisplacement




reliefdisplacement


To use the thermal infrared remote sensor data for practical purposes To use the thermal infrared remote sensor data for practical purposes such as temperature mapping, it is such as temperature mapping, it is necessary to calibrate the brightness necessary to calibrate the brightness values values stored on the digital tape to temperature values. This radiometric stored on the digital tape to temperature values. This radiometric calibration may be performed using:calibration may be performed using:

•• internal blackbody source referencinginternal blackbody source referencing, or , or

• • external empirical referencing based on external empirical referencing based on in situ in situ data collectiondata collection..

To use the thermal infrared remote sensor data for practical purposes To use the thermal infrared remote sensor data for practical purposes such as temperature mapping, it is such as temperature mapping, it is necessary to calibrate the brightness necessary to calibrate the brightness values values stored on the digital tape to temperature values. This radiometric stored on the digital tape to temperature values. This radiometric calibration may be performed using:calibration may be performed using:

•• internal blackbody source referencinginternal blackbody source referencing, or , or

• • external empirical referencing based on external empirical referencing based on in situ in situ data collectiondata collection..

Radiometric Calibration of Radiometric Calibration of Thermal Scanner DataThermal Scanner Data

Radiometric Calibration of Radiometric Calibration of Thermal Scanner DataThermal Scanner Data

External Empirical Referencing of External Empirical Referencing of Thermal Infrared ImageryThermal Infrared Imagery

External Empirical Referencing of External Empirical Referencing of Thermal Infrared ImageryThermal Infrared Imagery

It is possible to make both linear and area arrays that are sensitive to mid- and thermal It is possible to make both linear and area arrays that are sensitive to mid- and thermal infrared radiation.infrared radiation. Linear and area arrays allow improved thermal infrared remote Linear and area arrays allow improved thermal infrared remote sensing to take place becausesensing to take place because::

•• the solid-state microelectronic detectors are smaller in size (e.g. 20 x 20 mm) and the solid-state microelectronic detectors are smaller in size (e.g. 20 x 20 mm) and weight, require less power to operate, have fewer moving parts, and are more reliable;weight, require less power to operate, have fewer moving parts, and are more reliable;

•• each detector in the array can view the ground resolution element for a longer time each detector in the array can view the ground resolution element for a longer time (i.e. it is as longer dwell time), allowing more photons of energy from within the IFOV (i.e. it is as longer dwell time), allowing more photons of energy from within the IFOV to be recorded by the individual detector resulting in improved radiometric resolution to be recorded by the individual detector resulting in improved radiometric resolution (the ability to resolve smaller temperature differences);(the ability to resolve smaller temperature differences);

•• each detector element in the linear or area array is fixed relative to all other elements each detector element in the linear or area array is fixed relative to all other elements therefore the geometry of the thermal infrared image is much improved relative to that therefore the geometry of the thermal infrared image is much improved relative to that produced by an across-track scanning system; andproduced by an across-track scanning system; and•• some linear and area thermal detectors do not even require the cooling apparatus.some linear and area thermal detectors do not even require the cooling apparatus.

It is possible to make both linear and area arrays that are sensitive to mid- and thermal It is possible to make both linear and area arrays that are sensitive to mid- and thermal infrared radiation.infrared radiation. Linear and area arrays allow improved thermal infrared remote Linear and area arrays allow improved thermal infrared remote sensing to take place becausesensing to take place because::

•• the solid-state microelectronic detectors are smaller in size (e.g. 20 x 20 mm) and the solid-state microelectronic detectors are smaller in size (e.g. 20 x 20 mm) and weight, require less power to operate, have fewer moving parts, and are more reliable;weight, require less power to operate, have fewer moving parts, and are more reliable;

•• each detector in the array can view the ground resolution element for a longer time each detector in the array can view the ground resolution element for a longer time (i.e. it is as longer dwell time), allowing more photons of energy from within the IFOV (i.e. it is as longer dwell time), allowing more photons of energy from within the IFOV to be recorded by the individual detector resulting in improved radiometric resolution to be recorded by the individual detector resulting in improved radiometric resolution (the ability to resolve smaller temperature differences);(the ability to resolve smaller temperature differences);

•• each detector element in the linear or area array is fixed relative to all other elements each detector element in the linear or area array is fixed relative to all other elements therefore the geometry of the thermal infrared image is much improved relative to that therefore the geometry of the thermal infrared image is much improved relative to that produced by an across-track scanning system; andproduced by an across-track scanning system; and•• some linear and area thermal detectors do not even require the cooling apparatus.some linear and area thermal detectors do not even require the cooling apparatus.

Push-broom Linear and Area Array Push-broom Linear and Area Array Charge-coupled device (CCD) DetectorsCharge-coupled device (CCD) Detectors

Push-broom Linear and Area Array Push-broom Linear and Area Array Charge-coupled device (CCD) DetectorsCharge-coupled device (CCD) Detectors

•• For decades, the military organizations throughout the For decades, the military organizations throughout the world have funded the development of FLIR type systems world have funded the development of FLIR type systems that look obliquely ahead of the aircraft and acquire high-that look obliquely ahead of the aircraft and acquire high-quality thermal infrared imagery, especially at night. quality thermal infrared imagery, especially at night.

•• FLIR systems collect the infrared energy based on the FLIR systems collect the infrared energy based on the same principles as an across-track scanner previously same principles as an across-track scanner previously discussed, except that the mirror points forward about 45˚ discussed, except that the mirror points forward about 45˚ and projects terrain energy during a single sweep of the and projects terrain energy during a single sweep of the mirror onto a linear array of thermal infrared detectors. mirror onto a linear array of thermal infrared detectors.

•• For decades, the military organizations throughout the For decades, the military organizations throughout the world have funded the development of FLIR type systems world have funded the development of FLIR type systems that look obliquely ahead of the aircraft and acquire high-that look obliquely ahead of the aircraft and acquire high-quality thermal infrared imagery, especially at night. quality thermal infrared imagery, especially at night.

•• FLIR systems collect the infrared energy based on the FLIR systems collect the infrared energy based on the same principles as an across-track scanner previously same principles as an across-track scanner previously discussed, except that the mirror points forward about 45˚ discussed, except that the mirror points forward about 45˚ and projects terrain energy during a single sweep of the and projects terrain energy during a single sweep of the mirror onto a linear array of thermal infrared detectors. mirror onto a linear array of thermal infrared detectors.

Forward-Looking Infrared (FLIR) SystemsForward-Looking Infrared (FLIR) SystemsForward-Looking Infrared (FLIR) SystemsForward-Looking Infrared (FLIR) Systems

Forward Looking Infrared (FLIR)

Examples

Forward Looking Infrared (FLIR)

Examples

•• The The diurnal cyclediurnal cycle encompasses 24 hours. Beginning at sunrise, the earth begins encompasses 24 hours. Beginning at sunrise, the earth begins intercepting mainly short wavelength energy (0.4 - 0.7 intercepting mainly short wavelength energy (0.4 - 0.7 m) from the Sun. From about m) from the Sun. From about 6:00 am to 8:00 pm, the terrain intercepts the incoming short wavelength energy and 6:00 am to 8:00 pm, the terrain intercepts the incoming short wavelength energy and reflects much of it back into the atmosphere where we can use optical remote sensors to reflects much of it back into the atmosphere where we can use optical remote sensors to measure the reflected energy. However, some of the incident short wavelength energy measure the reflected energy. However, some of the incident short wavelength energy is absorbed by the terrain and then re-radiated back into the atmosphere as thermal is absorbed by the terrain and then re-radiated back into the atmosphere as thermal infrared long wavelength radiation (3 - 14 infrared long wavelength radiation (3 - 14 m). The outgoing longwave radiation m). The outgoing longwave radiation reaches its highest value during the day when the surface temperature is highest. This reaches its highest value during the day when the surface temperature is highest. This peak usually lags two to four hours after the midday peak of incoming shortwave peak usually lags two to four hours after the midday peak of incoming shortwave radiation, owing to the time taken to heat the soil. The contribution of reflected short radiation, owing to the time taken to heat the soil. The contribution of reflected short wavelength energy and emitted long wavelength energy causes an energy surplus to wavelength energy and emitted long wavelength energy causes an energy surplus to take place during the day. Both incoming and outgoing shortwave radiation become take place during the day. Both incoming and outgoing shortwave radiation become zero after sunset (except for light from the moon and stars), but outgoing longwave zero after sunset (except for light from the moon and stars), but outgoing longwave radiation continues all night. radiation continues all night.

•• The The diurnal cyclediurnal cycle encompasses 24 hours. Beginning at sunrise, the earth begins encompasses 24 hours. Beginning at sunrise, the earth begins intercepting mainly short wavelength energy (0.4 - 0.7 intercepting mainly short wavelength energy (0.4 - 0.7 m) from the Sun. From about m) from the Sun. From about 6:00 am to 8:00 pm, the terrain intercepts the incoming short wavelength energy and 6:00 am to 8:00 pm, the terrain intercepts the incoming short wavelength energy and reflects much of it back into the atmosphere where we can use optical remote sensors to reflects much of it back into the atmosphere where we can use optical remote sensors to measure the reflected energy. However, some of the incident short wavelength energy measure the reflected energy. However, some of the incident short wavelength energy is absorbed by the terrain and then re-radiated back into the atmosphere as thermal is absorbed by the terrain and then re-radiated back into the atmosphere as thermal infrared long wavelength radiation (3 - 14 infrared long wavelength radiation (3 - 14 m). The outgoing longwave radiation m). The outgoing longwave radiation reaches its highest value during the day when the surface temperature is highest. This reaches its highest value during the day when the surface temperature is highest. This peak usually lags two to four hours after the midday peak of incoming shortwave peak usually lags two to four hours after the midday peak of incoming shortwave radiation, owing to the time taken to heat the soil. The contribution of reflected short radiation, owing to the time taken to heat the soil. The contribution of reflected short wavelength energy and emitted long wavelength energy causes an energy surplus to wavelength energy and emitted long wavelength energy causes an energy surplus to take place during the day. Both incoming and outgoing shortwave radiation become take place during the day. Both incoming and outgoing shortwave radiation become zero after sunset (except for light from the moon and stars), but outgoing longwave zero after sunset (except for light from the moon and stars), but outgoing longwave radiation continues all night. radiation continues all night.

Diurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical Materials

Peak Period of Daily Peak Period of Daily Outgoing Longwave Outgoing Longwave

Radiation and the Diurnal Radiation and the Diurnal Radiant Temperature of Radiant Temperature of

Soils and Rocks, Soils and Rocks, Vegetation, Water, Moist Vegetation, Water, Moist Soil and Metal ObjectsSoil and Metal Objects

Peak Period of Daily Peak Period of Daily Outgoing Longwave Outgoing Longwave

Radiation and the Diurnal Radiation and the Diurnal Radiant Temperature of Radiant Temperature of

Soils and Rocks, Soils and Rocks, Vegetation, Water, Moist Vegetation, Water, Moist Soil and Metal ObjectsSoil and Metal Objects

•• If all the curves for soils and rocks, water, vegetation, moist soil, and metal objects lie If all the curves for soils and rocks, water, vegetation, moist soil, and metal objects lie exactly on top of one another, then remote sensing in the thermal infrared portion of the exactly on top of one another, then remote sensing in the thermal infrared portion of the spectrum would be of no value because all the phenomena would have the same spectrum would be of no value because all the phenomena would have the same apparent radiant temperature. There would be no contrast in the imagery between the apparent radiant temperature. There would be no contrast in the imagery between the different phenomena. Fortunately, there are only two times during the day (after sunrise different phenomena. Fortunately, there are only two times during the day (after sunrise and near sunset) when some materials like soils and rocks and water have exactly the and near sunset) when some materials like soils and rocks and water have exactly the same radiant temperature. During this same radiant temperature. During this crossovercrossover time period it is not wise to acquire time period it is not wise to acquire thermal infrared remotely sensed data.thermal infrared remotely sensed data.

•• Fortunately, some materials store heat more efficiently that others, i.e. they have a Fortunately, some materials store heat more efficiently that others, i.e. they have a higher thermal capacity. For example, water has a much higher thermal capacity than higher thermal capacity. For example, water has a much higher thermal capacity than soils and rocks). Its diurnal temperature range fluctuates very little when compared soils and rocks). Its diurnal temperature range fluctuates very little when compared with the dramatic temperature fluctuation of soils and rocks during a 24-hr period.with the dramatic temperature fluctuation of soils and rocks during a 24-hr period.

•• If all the curves for soils and rocks, water, vegetation, moist soil, and metal objects lie If all the curves for soils and rocks, water, vegetation, moist soil, and metal objects lie exactly on top of one another, then remote sensing in the thermal infrared portion of the exactly on top of one another, then remote sensing in the thermal infrared portion of the spectrum would be of no value because all the phenomena would have the same spectrum would be of no value because all the phenomena would have the same apparent radiant temperature. There would be no contrast in the imagery between the apparent radiant temperature. There would be no contrast in the imagery between the different phenomena. Fortunately, there are only two times during the day (after sunrise different phenomena. Fortunately, there are only two times during the day (after sunrise and near sunset) when some materials like soils and rocks and water have exactly the and near sunset) when some materials like soils and rocks and water have exactly the same radiant temperature. During this same radiant temperature. During this crossovercrossover time period it is not wise to acquire time period it is not wise to acquire thermal infrared remotely sensed data.thermal infrared remotely sensed data.

•• Fortunately, some materials store heat more efficiently that others, i.e. they have a Fortunately, some materials store heat more efficiently that others, i.e. they have a higher thermal capacity. For example, water has a much higher thermal capacity than higher thermal capacity. For example, water has a much higher thermal capacity than soils and rocks). Its diurnal temperature range fluctuates very little when compared soils and rocks). Its diurnal temperature range fluctuates very little when compared with the dramatic temperature fluctuation of soils and rocks during a 24-hr period.with the dramatic temperature fluctuation of soils and rocks during a 24-hr period.

Diurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical MaterialsDiurnal Temperature Cycle of Typical Materials

Solomon Blatt Fieldhouse on the University of South

Carolina Campus

Solomon Blatt Fieldhouse on the University of South

Carolina Campus

March 10, 19834:30 am

0.5 x 0.5 m

March 10, 19834:30 am

0.5 x 0.5 m

a. b. Vertical Aerial PhotographPre-dawn Thermal Infrared Imagemetal ventoverhangingeaves

a. b. Vertical Aerial PhotographPre-dawn Thermal Infrared Imagemetal ventoverhangingeaves

Blackbody Radiation Blackbody Radiation Curves for Several Curves for Several Objects including Objects including

the Sun and the Earththe Sun and the Earth

Blackbody Radiation Blackbody Radiation Curves for Several Curves for Several Objects including Objects including

the Sun and the Earththe Sun and the EarthR

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Documents

John R. Jensen Department of Geography University of South Carolina Columbia, South Carolina 29208 John R. Jensen Department of Geography University of