Topics to be Covered Thermal Radiation Laws Emissivity of Natural Terrain Heat Conduction Theory Effect of Periodic Heating Surface Heating by the Sun Thermal Infrared Spectral Signatures Example Sensor AVHRR ID: 755953
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Slide1
EE/Ae 157a
Week 5: Thermal InfraredSlide2
Topics to be Covered
Thermal Radiation Laws
Emissivity of Natural Terrain
Heat Conduction Theory
Effect of Periodic Heating
Surface Heating by the Sun
Thermal Infrared Spectral Signatures
Example Sensor: AVHRRSlide3
Infrared Spectrum
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide4
Thermal Radiation Laws
Heat energy is a special case of EM radiation
The random motion (due to collisions) of the molecules due to kinetic energy results in exitation (electronic, vibrational and rotational) followed by random emissions during decay
This leads to radiation over a large bandwidth according to Planck’s law for an ideal source (called a black body)
Thermal emission is usually unpolarizedSlide5
Blackbody RadiationSlide6
Stefan-Boltzmann Law
The total flux emitted by a blackbody of unit area is found by integrating the emittance over the whole spectrum:
This is known as the Stefan-Boltzmann lawSlide7
Wien’s Law
Wien’s law expresses the wavelength of maximum emittance for a blackbody:
The value of the emittance at isSlide8
Emissivity of Natural Terrain
All natural terrains are characterized by a spectral emissivity factor
The mean emissivity factor is
Blackbodies have
Graybodies have
Selective radiators have spectral emissivity factor that varies with wavelengthSlide9
Example Emissivities
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide10
Kinetic and Radiant Temperatures
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide11
Reflection and Emission from Sun and Planets
From Elachi, Chapter 4
Solid Line: Reflected Power
Dashed Line: Emitted Power
The total observed power from a planet is the sum of incoming solar energy that is reflected and the power emitted from the planet itself:
Remember that
Slide12
Spitzer Detects Debris DisksSlide13
Effect of Clouds on Thermal IR Images
Visible
Thermal IRSlide14
Effects of Weather on Thermal IR Images
Clouds
Wind
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide15
Thermal IR Energy Penetrates Smoke
Visible Image
Thermal IR Image
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide16
Nighttime Thermal IR Images
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide17
Effect of Wavelength in Thermal IR Images
3-5
microns
8-14
microns
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide18
Malibu Forest FiresSlide19
Bull Run, VirginiaSlide20
Heat Conduction Theory
The heat conduction equation is
K
is the material thermal conductivity (Cal/m/sec/degree),
r
is the material density (kg/m
3
) and
C is the material specific heat capacity (Cal/kg/degree)If K is not constant, then the heat equation becomesSlide21
Effect of Periodic Heating
The case of a semi-infinite solid with a surface temperature which is a harmonic function of time is of particular interest in remote sensing because of the periodic surface heating from the sun
The surface temperature of the solid is
The solution to the heat conduction equation isSlide22
Temperature Wave as Function of Depth
From Elachi, Chapter 4Slide23
Diurnal Temperature Curves
From Elachi, Chapter 4Slide24
Examples of Apparent Thermal Inertia
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide25
Daytime and Nighttime Thermal IR Images
Day
Night
From
Remote Sensing: Principles and Interpretation
by Floyd F. SabinsSlide26
Crater on MarsSlide27
Transmission through Quartz
From Elachi, Chapter 4Slide28
Transmission Spectra for Common Silicates
From Elachi, Chapter 4Slide29
Death Valley, California
Visible
SWIR
TIRSlide30
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)Slide31
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)Slide32
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)Slide33
ASTER: Thermal Infrared
Cryocooler - The ten Mercury-Cadmium-Telluride detectors in each of the five TIR channels are cooled to 80 K using a mechanical split Stirling cycle cooler of long life and low vibration design.
Reference Plate (Black Body) - A high emissivity reference plate is used as the on-board calibration reference for the TIR subsystem. This reference plate is viewed before and after each observation to provide an estimate of instrument drift and periodically this plate is heated through a range of temperature to provide an estimate for both instrument gain and offset.
Scan Mirror - The scan mirror is used for both scanning and pointing. In the scanning mode the mirror oscillates across the ground track at about 7 Hz. This mirror can point +/- 8.54 degrees from the nadir direction to allow coverage of any point on the earth over the spacecraft's 16 day mapping cycle. This mirror can also rotate 180 degrees from the nadir direction to provide a view of the reference plate for calibration.
Telescope - The TIR subsystem uses a Newtonian catadioptric system with an aspheric primary mirror and lens for aberration correction. Unlike the VNIR telescope, the telescope of the TIR subsystem is fixed and both pointing and scanning is done by the mirror.Slide34
Detector Landscape
> 1 mm
100-1000 um
10-100 um
1-10 um
0.1-1 um
10-100 nm
1-10 nm
mmWave
Sub-mm
FIR
MIR
NIR
Vis
UV
TECHNOLOGIES
SC Calorimeter
CCD
Micro Channel Plate
CMOS
InGaAs
Si: As
QWIP
InSb
SC Bolometer
HEB
SIS
Schottky
InP HEMT
GaN
Ge: Ga
Si: Sb
HgCdTe
CCD Calorimeter
Uncooled Bolo
Commercial and defense applications in terrestrial imaging and sensing
strong technical infrastructure
synergistic funding
Commercial and defense applications in comms and radar
Primarily driven by space based astrophysics
weak infrastructure
limited funding
great science
SAFIR
strong technical infrastructure
synergistic fundingSlide35
24
m
m
70
m
m
CSMM
160
m
m
MIPS Critical Elements:
Focal Planes, Filters, and Scan Mirror
24
m
m array provided
through the IRS
program
Cryogenic scan
mirror mechanism
built @ Ball based on
design from ISO
Short Wavelength
Spectrometer
70 & 160
m
m
arrays developed
at University of AZ
Far infrared
filters (over 70
m
m
array) from Queen
Mary CollegeSlide36
ASTER ImagesSlide37
Principal ComponentsSlide38
Sharpened Principal Component ImageSlide39
Lake Tahoe, CaliforniaSlide40
Sea Surface Temperatures
Hurricane GeorgesSlide41
Sea Surface Temperature
Gulf StreamSlide42
Sea Surface Temperature
Agulhas and Benguela CurrentsSlide43
Mean Sea Surface TemperatureSlide44
Average Sea Surface Temperature in Dec