Thermal IR February 23, 2005 Thermal Properties Thermal IR Atmospheric Windows Thermal IR...
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Transcript of Thermal IR February 23, 2005 Thermal Properties Thermal IR Atmospheric Windows Thermal IR...
• Thermal Properties• Thermal IR Atmospheric Windows• Thermal IR Environmental Considerations• Thermal Radiation Laws• Emissivity
• Reminder: Read rest of Chapter 8 for next class• Midterm Exam on Monday. Review sheet is posted!
Thermal IR
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 Airport
• Kinetic Temperature (Tkin) – true kinetic temperature• Radiant Temperature (Trad) – temperature calculated from radiant exitance (radiant flux)• Usually a pretty darn good correlation, but not always!!• Depends on the thermal emissivity of an object (and discussed later in this chapter).
Thermal Properties
Atmospheric Windows in the Electromagnetic SpectrumAtmospheric Windows in the Electromagnetic Spectrum
Where are the Thermal IR atmospheric windows?
• Thermal IR region of the EM Spectrum is from 3 to 14 µm• Three primary windows:
– 3 - 5 µm– 8 - 9.2 µm– 10.5 – 12.5 µm
Thermal IR Atmospheric Windows
Peak Period of Daily Outgoing Longwave
Radiation and the Diurnal Radiant Temperature of
Soils and Rocks, Vegetation, Water, Moist
Soil and Metal Objects
Peak Period of Daily Outgoing Longwave
Radiation and the Diurnal Radiant Temperature of
Soils and Rocks, Vegetation, Water, Moist
Soil and Metal Objects
When is/are the best time(s) of day to acquire thermal imagery? Why?
When is/are the worst time(s) of day to acquire thermal imagery? Why?
Thermal Infrared Radiation PrinciplesThermal Infrared Radiation Principles
• An analyst cannot interpret a thermal infrared image as if it were an aerial photograph or a normal image produced by a multispectral scanner or charge-coupled device.
• Rather, the image analyst must think thermally.
• The analyst must understand how energy from the Sun or from the Earth interacts with the various terrain components and how the detectors function as they record the terrain’s emitted thermal infrared electromagnetic radiation.
• An analyst cannot interpret a thermal infrared image as if it were an aerial photograph or a normal image produced by a multispectral scanner or charge-coupled device.
• Rather, the image analyst must think thermally.
• The analyst must understand how energy from the Sun or from the Earth interacts with the various terrain components and how the detectors function as they record the terrain’s emitted thermal infrared electromagnetic radiation.
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 Residential Subdivision in Forth Worth, Texas
Pre-dawn Thermal Infrared Image of a Residential Subdivision in Forth Worth, Texas
a b
c
d
e
f
h
g
a b
c
d
e
f
h
g
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
Daytime Optical and Nighttime Thermal
Infrared Imagery of the University of South
Carolina Campus
Daytime Optical and Nighttime Thermal
Infrared Imagery of the University of South
Carolina Campus
April 26, 19814:56 am 1 x 1 m
April 26, 19814:56 am 1 x 1 m
2x reduction
steam lines
steam plant
manhole cover
library
parking
soccer field
dorms
one-dimensional relief
displacement
Vertical Aerial Photograph
Pre-dawn Thermal Infrared Image
line-of-flight
science buildings
a.
b.
steam lines
steam plant
manhole cover
library
parking
soccer field
dorms
one-dimensional relief
displacement
Vertical Aerial Photograph
Pre-dawn Thermal Infrared Image
line-of-flight
science buildings
a.
b.
• Blackbody – Theoretical construct that absorbs and radiates energy at the maximum possible. • Wien’s Displacement Law – Dominant wavelength is inversely proportional to temperature. Thermal Radiation Laws
Blackbody Radiation Curves for Several
Objects including the Sun and Earth
Blackbody Radiation Curves for Several
Objects including the Sun and Earth
For example, the average temperature of the Earth is 300 K (80 ˚F).
We compute the Earth’s dominant wavelength as:
max = 2898 m K
T
max = 2898 m K = 9.67 m
300 K
For example, the average temperature of the Earth is 300 K (80 ˚F).
We compute the Earth’s dominant wavelength as:
max = 2898 m K
T
max = 2898 m K = 9.67 m
300 K
Wein’s Displacement LawWein’s Displacement Law
• The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 K forest fires that have a dominant wavelength of approximately 3.62 m then the most appropriate remote sensing system might be a 3-5 m thermal infrared detector.
• If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 K and a dominant wavelength of 9.66 m, then a thermal infrared detector operating in the 8 - 14 m region might be most appropriate.
• The dominant wavelength provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are looking for 800 K forest fires that have a dominant wavelength of approximately 3.62 m then the most appropriate remote sensing system might be a 3-5 m thermal infrared detector.
• If we are interested in soil, water, and rock with ambient temperatures on the earth’s surface of 300 K and a dominant wavelength of 9.66 m, then a thermal infrared detector operating in the 8 - 14 m region might be most appropriate.
Wein’s Displacement LawWein’s Displacement Law
• The world is not composed of radiating blackbodies. Rather it is composed of selectively radiating bodies such as rocks, soil, and water that emit only a fraction of the energy emitted from a blackbody at the same temperature. Emissivity, , is the ratio between the radiant flux exiting a real-world selective radiating body (Fr) and a blackbody at the same temperature (Fb):
Fr
= ______
Fb
• The world is not composed of radiating blackbodies. Rather it is composed of selectively radiating bodies such as rocks, soil, and water that emit only a fraction of the energy emitted from a blackbody at the same temperature. Emissivity, , is the ratio between the radiant flux exiting a real-world selective radiating body (Fr) and a blackbody at the same temperature (Fb):
Fr
= ______
Fb
EmissivityEmissivity
• 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 µm. 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 µm. Others such as polished aluminum (0.08) and stainless steel (0.16) have very low emissivities.
EmissivityEmissivity
• No objects in the world are true blackbodies; rather, they are selectively radiating bodies.• Emissivity (є) is the ratio between the radiant flux exiting a real world selective radiating body (M r) and a blackbody at the same temperature (Mb).
• A graybody outputs a constant emissivity that is less than one at all wavelengths.
Emissivity
Spectral emissivity of a blackbody, a graybody,
and a hypothetical selective radiator
Spectral emissivity of a blackbody, a graybody,
and a hypothetical selective radiator
2x reduction2x reduction
1
0.5
0.1
0.1 1 10 100
0.1 100
100101
102
104
106
108
Wavelength, m
Wavelength, m
Spec
tral
Em
issi
vity
,
Spec
tral
Rad
iant
Exi
tanc
e
W m
-2
m-1
selective radiator
blackbody
6,000 ÞK blackbody = 1.0
graybody
6,000 ÞK graybody = 0.1
6,000 ÞK selective radiator
a.
b.
1
0.5
0.1
0.1 1 10 100
0.1 100
100101
102
104
106
108
Wavelength, m
Wavelength, m
Spec
tral
Em
issi
vity
,
Spec
tral
Rad
iant
Exi
tanc
e
W m
-2
m-1
selective radiator
blackbody
6,000 ÞK blackbody = 1.0
graybody
6,000 ÞK graybody = 0.1
6,000 ÞK selective radiator
a.
b.
Spectral radiant exitance distribution of
the blackbody, graybody, and
hypothetical selective radiator
Spectral radiant exitance distribution of
the blackbody, graybody, and
hypothetical selective radiator
Spec
tral
Em
issi
vity
, eSp
ectr
al R
adia
nt E
xita
nce
W m
-2 u
m-1
• What is the difference between thermal capacity, thermal conductivity, and thermal inertia?
• Thermal capacity (c) is the ability of a material to store heat. It is measured as the number of calories required to raise a gram of material (e.g., water) 1 ˚C (cal g-1 ˚C-1).
• Thermal conductivity (K) is the rate that heat will pass through a 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 are maintained at 1 ˚C difference in temperature (cal cm-1 sec-1 ˚C).
• Thermal capacity (c) is the ability of a material to store heat. It is measured as the number of calories required to raise a gram of material (e.g., water) 1 ˚C (cal g-1 ˚C-1).
• Thermal conductivity (K) is the rate that heat will pass through a 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 are maintained at 1 ˚C difference in temperature (cal cm-1 sec-1 ˚C).
Thermal Properties of TerrainThermal Properties of Terrain
• Thermal inertia (P) is a measurement of the thermal response of a material to temperature changes and is measured in calories per square centimeter per second square root per degree Celsius (cal cm-2
sec -1/2 ˚C-1). Thermal inertia is computed using the equation:
P = (K x p x c)1/2
where K is thermal conductivity, p is density (g cm-3), and c is thermal capacity. Density is the most important property in this equation because thermal inertia generally increases linearly with increasing material density.
• Thermal inertia (P) is a measurement of the thermal response of a material to temperature changes and is measured in calories per square centimeter per second square root per degree Celsius (cal cm-2
sec -1/2 ˚C-1). Thermal inertia is computed using the equation:
P = (K x p x c)1/2
where K is thermal conductivity, p is density (g cm-3), and c is thermal capacity. Density is the most important property in this equation because thermal inertia generally increases linearly with increasing material density.
Thermal InertiaThermal Inertia
There is an inverse relationship between having high spatial resolution and high radiometric resolution when collecting thermal infrared data.
There is an inverse relationship between having high spatial resolution and high radiometric resolution when collecting thermal infrared data.
Thermal Infrared Remote SensingThermal Infrared Remote Sensing
Forward Looking Infrared (FLIR)
Examples
Forward Looking Infrared (FLIR)
Examples