Infrared
Infrared Electromagnetic wave
length
Infrared light has a range of wavelengths, just
like visible light has. "Near infrared" light is
closest in wavelength to visible light and "far
infrared" is closer to the microwave region of the
electromagnetic spectrum.
 Far infrared waves are in the thermal band and
can measure the temperature of an object. The
range is centered on 3 micrometers in length
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Humans, at normal body temperature,
radiate most strongly in the infrared at a
wavelength of about 10 microns. (A
micron is the term commonly used in
astronomy for a micrometer or one
millionth of a meter.)
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Landsat 7 satellite, Modis satellite, and
Astor satellite record data about the
amount of infrared light reflected or
emitted from the Earth's surface.
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Using different bands the Satellite can
calculate the temperature of the surface
but only to within 1.5 degrees of the
correct value.
Infrared Thermometer
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Infrared thermometor
Crop water stress index
Cwsi
 Accurate measurement of the leaf to
air temperature require that leaf
temperature must be known to
within about ±0.1°C.
 That is why satellite data can not be
used to directly measure the CWSI
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Infrared thermometers are filtered to allow only a
specific waveband, about 8 to 14 microns, to be
transmitted to the IRT detector.
This transmitted energy (E) is converted to
temperature (T) via the Stefan-Boltzman Law
which states E=esT4, where e is the emissivity of
the object and s is the Stefan-Boltzmann constant
(5.68 x 10-8 Joules m-2 s-1 K-4).
Emissivity is defined as the radiation efficiency of
a surface as compared to an ideal "black body"
emitter. The emissivity of plants is 0.98.
Calibration of Infrared sensor
A water cone calibrator can be built using a a 2
L beaker filled with water and placed on a
magnetic stirring hot plate.
 The water has to be stirred with a large stirring
bar so that the vortex produced a deep cone
shape on the surface, which increased the
effective emissivity of the water which is 0.96.
 The water temperature is measured with
thermocouples placed in the beaker.
 Change the thermostat on the heater and
measure the temperature from the
thermocouples and infrared sensor.
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Corrected Target Temperature =
Apparent Target temperature – Error
 Error=(0.25/P(sb))*[((Apparent
Target Temperature - H(sb))^2 ) K(sb) ]
 Sb is the sensor body temperature.
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Where
 P(sb) = 26.168 + 2.8291*SB 0.03329*SB^2
 H(sb) = 5.8075 - 0.08016*SB +
8.49e-3*SB^2
 K(sb) =-85.943 + 11.740*SB +
0.08477*SB^2
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The sensor can be read by a Fluke Digital
Thermometers
 Or a Campbell data logger.
 The Fluke digital thermometer measures
and stores the target temperature and the
body temperature.
 Down load the data and analysis in a excel
spreadsheet.
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The thermocouple areType K (ChromelAlumel)
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Set the thermocouple type in the Fluke.
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See instructions and move