Lecture 5 thermal infrared remote sensing september 30 2003
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Lecture 5 Thermal Infrared Remote Sensing September 30, 2003. Reading Assignment. Jensen – Chapter 8 Unless otherwise noted, all images in this lecture are from

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Lecture 5 thermal infrared remote sensing september 30 2003

Lecture 5Thermal Infrared Remote SensingSeptember 30, 2003


Reading assignment

Reading Assignment

  • Jensen – Chapter 8

    Unless otherwise noted, all images in this lecture are from

    • Jensen, J.R., Remote Sensing of the Environment - An Earth Resource Perspective, 544 pp., Prentice Hall, Upper Saddle River, NJ, 2000.


Lecture 5 thermal infrared remote sensing september 30 2003

AVHRR Image of land and sea surface temperature from thermal IR radiance measurements

Red – warmest

Orange

Yellow

Green

Blue

Purple - coldest

Image from -http://rs.gso.uri.edu/amy/avhrr.html


Lecture 5 thermal infrared remote sensing september 30 2003

Signature Detected by a

Thermal Radiometer

Thermal IR

Radiometer

Ls

Lp 

Lt 

Ma

emitted energy from the atmosphere

Mt– emitted energy

Target


Sources of surface temperature variations gain and loss

Sources of surface temperature variations - gain and loss

  • Absorbed short-wavelength EM energy absorbed (from energy emitted from the sun) (heat gain)

  • Long-wavelength EM energy emitted from the earth’s surface (heat loss)

  • Combustion

    • Human vs. natural

    • Direct vs. indirect

  • Geothermal

    • Volcanoes

    • Hot springs


Stefan boltzman law

Stefan-Boltzman Law

  • The amount of EM radiation (M) emitted from a body in Watts m-2 (the exitance) can be calculated as

    M =  T4

    where  is a constant and

    T4 is the temperature in degrees Kelvin


Wien displacement law

Wien Displacement Law

  • The wavelength with the highest level of emitted radiation (max) for an object of temperature T can be calculated as

    max = k / T

    where k = 2898 m ºK


Examples of wien s displacement law

T (sun) = 6000º K

max = k / T

= 2898/6000

= 0.483 m

T (earth) = 300º K

max = k / T

= 2898/300

= 9.66 m

Examples of Wien’s Displacement Law


Kinetic heat t kin

Kinetic Heat - Tkin

  • Kinetic heat (internal or true heat) is the energy of particles of molecular matter in random motion

  • When particles collide, they generate radiant energy or electromagnetic radiation

  • Tkinis the true kinetic temperature, measured with a thermometer


Radiant temperature t rad

Radiant Temperature - Trad

  •  - radiant flux – the amount of radiant energy per unit time pass through or from an object

  • Trad is simply the radiant flux being emitted by an object because of its temperature, i.e., the radiant temperature

  • Trad does not always equal Tkin


Perfect radiator or blackbody

Perfect Radiator or Blackbody

A theoretical object or surface that

  • Absorbs all the radiation that falls upon it

  • Radiates energy at the maximum rate possible at all wavelengths


Emissivity

Emissivity - 

Emissivity defines the amount of radiation emitted from a body or surface (Mr ) relative to the exitance of a blackbody

(Mb ) at the same temperature

 = Mr / Mb


Factors influencing emissivity

Factors influencing emissivity

  • Material

  • Surface roughness

  • Moisture content

  • Compaction

  • EM wavelength

  • Viewing angle


Graybody and selective emitters

Graybody and Selective Emitters

  • Graybody emitters are those whose emittance is less than a perfect radiator with the same temperature, but whose emissions

    • are constant for any wavelength

    • are a consistent fraction of the perfect radiator or blackbody emittance

  • Selective emitters are bodies whose emittance is less than a perfect radiator or black body with the same temperature, but not constant as a function of wavelength


Kirchoff s radiation law

Kirchoff’s Radiation Law

For any object that intercepts EM radiant energy

r +  +  = 1

at thermal IR wavelengths,

 = 0 and  = 

Therefore

1 = r + 


Lecture 5 thermal infrared remote sensing september 30 2003

Table 8-1 from text


Non blackbody exitance

Non-Blackbody Exitance

  • If a surface or body has an emissivity of , then its emittance, Mr, is

    Mr =   Tkin4

    where

  • is the Stephan-Boltzman constant

    Tkin is the kinetic temperature


Apparent radiant temperature t rad

Apparent Radiant Temperature - Trad

  •  - radiant flux – the amount of radiant energy per unit time pass through or from an object

  • Trad is simply the radiant flux being emitted by an object because of its temperature, the radiant temperature


Radiant vs kinetic temperature

Radiant vs. Kinetic Temperature

Trad = 1/4 Tkin


Sources of surface temperature variations gain and loss1

Sources of surface temperature variations - gain and loss

  • Short-wavelength EM energy absorbed from energy emitted from the sun

  • Long-wavelength EM energy emitted to the atmosphere

  • Combustion

    • Human vs. natural

    • Direct vs. indirect

  • Geothermal

    • Volcanoes

    • Hot springs


Lecture 5 thermal infrared remote sensing september 30 2003

Sources of Signatures Detected by a

Thermal Radiometer

The Atmosphere -

Thermal IR

Radiometer

Ls

Eo

  • a-sw - absorption coefficient for shortwave EM radiation

    To – transmission coefficient

    Ed – path radiance

Target

 t-sw


Lecture 5 thermal infrared remote sensing september 30 2003

a-sw


Lecture 5 thermal infrared remote sensing september 30 2003

Sources of Signatures Detected by a

Thermal Radiometer

The Atmosphere -

Thermal IR

Radiometer

Ls

Eo

Lt 

  • a-sw - absorption coefficient for shortwave EM radiation

    To – transmission coefficient

    Ed – path radiance

Mt– emitted energy

Target

 t-sw, Tkin, 


Importance of albedo in thermal ir remote sensing

Importance of albedo in thermal IR remote sensing

  • On the land and ocean surface, the sun provides most of the energy that results in variations in surface temperature

  • Albedo is the fraction of incoming solar radiation that is reflected from the earth’s surface

  • Surfaces with high albedo absorb little solar energy and therefore tend to have little thermal IR variability

  • Surfaces with low albedo absorb much energy, and have the potential for high thermal IR variability


Lecture 5 thermal infrared remote sensing september 30 2003

Sources of Signatures Detected by a

Thermal Radiometer

The Atmosphere -

Thermal IR

Radiometer

Ls

Lt 

  • a-lw - absorption coefficient for longwave EM radiation

Mt– emitted energy

Target

 t-sw, Tkin, 


Lecture 5 thermal infrared remote sensing september 30 2003

a-lw


Lecture 5 thermal infrared remote sensing september 30 2003

Signature Detected by a

Thermal Radiometer

Thermal IR

Radiometer

Ls

Lp 

Lt 

Ma

emitted energy from the atmosphere

Mt– emitted energy

Target


Lecture 5 thermal infrared remote sensing september 30 2003

Signature Detected by a

Thermal Radiometer

Thermal IR

Radiometer

Ls

Lp 

Ma

a-sw + a-lw

 Ta

Reflected thermal IR energy

Target


Key points for lecture 6

Key Points for Lecture 6

  • Reasons for channel selection in spaceborne thermal IR radiometers  atmospheric window

  • Minerology mapping

  • FLIR

  • Sources of thermal IR signatures from earth’s surface – role of short-wave and long-wave radiation

  • Diurnal thermal signatures

  • Principal of mapping fires using coarse-resolution thermal IR systems


Lecture content

Lecture Content

  • Spaceborne Thermal IR Radiometers

  • Forward Looking Infrared Radiometers (FLIRs)

  • Natural sources of surface temperature variations

  • Mapping of fires using coarse resolution systems


Spaceborne thermal ir radiometers

Spaceborne Thermal IR Radiometers

  • Landsat

  • AVHRR

  • MODIS

  • ASTER


Lecture 5 thermal infrared remote sensing september 30 2003

Atmospheric Windows


Advanced spaceborne thermal emission and reflectance radiometer aster

Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER)

  • ASTER was launched in December, 1999

  • Jointly developed by U.S. and Japanese

  • 3 channels in the visible/near IR (reflectance)

  • 6 channels in the shortwave IR (reflectance)

  • 5 channels in the thermal IR (emittance)

  • Developed to discriminate different rock types (minerology)


Lecture 5 thermal infrared remote sensing september 30 2003

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


Lecture 5 thermal infrared remote sensing september 30 2003

Emittance spectra of different minerals

From:

http://www.gps.caltech.edu/~ge151/

tutorials/tut_2.shtml


Lecture 5 thermal infrared remote sensing september 30 2003

ASTER Image

Red = B3 (.76-.86 um)

Green = B2 (.63-.69 um)

Blue = B1 (.52 -.59 um)

NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team


Lecture 5 thermal infrared remote sensing september 30 2003

ASTER Image

Red = B4 (1.6 – 1.7 um)

Green = B6 (2.19 – 2.23 um)

Blue = B8 (2.30 – 2.37 um)

NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team


Lecture 5 thermal infrared remote sensing september 30 2003

ASTER Image

Red = B13 (10.3-11.0 um)

Green = B12 (8.9-9.3 um)

Blue = B10 (8.1-8.5 um)

NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

http://asterweb.jpl.nasa.gov/gallery/gallery.

htm?name=Saline


Lecture content1

Lecture Content

  • Spaceborne Thermal IR Radiometers

  • Forward Looking Infrared Radiometers (FLIRs)

  • Natural sources of surface temperature variations

  • Mapping of fires using coarse resolution systems


Forward looking infrared flir systems

Forward-Looking Infrared (FLIR) Systems

  • Infrared detection technology has been exploited to create scanning systems that can be used for local surveillance purposes

  • FLIR systems use an linear array of detectors that enable creating an image with a single scan or sweep of an area

  • Use an oblique viewing direction to scan areas being monitored


Helicopter mounted flir system

Helicopter-Mounted FLIR System


Flir images

FLIR Images


Lecture content2

Lecture Content

  • Spaceborne Thermal IR Radiometers

  • Forward Looking Infrared Radiometers (FLIRs)

  • Natural sources of surface temperature variations

  • Mapping of fires using coarse resolution systems


Sources of surface temperature variations gain and loss2

Sources of surface temperature variations - gain and loss

  • Absorbed short-wavelength EM energy absorbed (from energy emitted from the sun) (heat gain)

  • Long-wavelength EM energy emitted from the earth’s surface (heat loss)

  • Combustion

    • Human vs. natural

    • Direct vs. indirect

  • Geothermal

    • Volcanoes

    • Hot springs


Lecture 5 thermal infrared remote sensing september 30 2003

Signature Detected by a

Thermal Radiometer

Thermal IR

Radiometer

Ls

Lp 

Lt 

Ma

emitted energy from the atmosphere

Mt– emitted energy

Target


Lecture 5 thermal infrared remote sensing september 30 2003

Sources of Signatures Detected by a

Thermal Radiometer

The Atmosphere -

Thermal IR

Radiometer

Ls

Eo

  • a-sw - absorption coefficient for shortwave EM radiation

    To – transmission coefficient

    Ed – path radiance

Target

 t-sw


Lecture 5 thermal infrared remote sensing september 30 2003

Sources of Signatures Detected by a

Thermal Radiometer

The Atmosphere -

Thermal IR

Radiometer

Ls

Lt 

  • a-lw - absorption coefficient for longwave EM radiation

Mt– emitted energy

Target

 t-sw, Tkin, 


Lecture 5 thermal infrared remote sensing september 30 2003

Thermal history of helicopters


Lecture 5 thermal infrared remote sensing september 30 2003

Thermal capacity – the amount of energy required to raise one gram of the material by one degree C


Lecture content3

Lecture Content

  • Spaceborne Thermal IR Radiometers

  • Forward Looking Infrared Radiometers (FLIRs)

  • Natural sources of surface temperature variations

  • Mapping of fires using coarse resolution systems


Lecture 5 thermal infrared remote sensing september 30 2003

AVHRR Image of land and sea surface temperature from thermal IR radiance measurements

Red – warmest

Orange

Yellow

Green

Blue

Purple - coldest

Image from -http://rs.gso.uri.edu/amy/avhrr.html


Lecture 5 thermal infrared remote sensing september 30 2003

Coarse-resolution satellite pixel

Ground Temperature = 300 K

Fire Temperature = 800 K


Lecture 5 thermal infrared remote sensing september 30 2003

Background = 300 deg K


Key points for lecture 61

Key Points for Lecture 6

  • Kinetic versus radiant temperature

  • Blackbody, graybody, and selective emitters

  • Emissivity – definition and factor influencing it

  • Kirchoff’s radiations laws

  • Role of atmospheric absorption, difference between shortwave and longwave absorptance

  • Source of path radiance in signal detected by thermal IR radiometer


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