Infrared Spectroscopy of the Atmosphere
using the FTIR Spectrometer
Brian EchevarriaJennifer Link
Introduction to Atmospheric Instrumentation (ATMS 360)
University of Nevada Reno
FTIRFourier Transform InfraRed
The FTIR Spectrometer is an optical instrument used to measure infrared spectra from 5 microns to 20 microns. Interested in the window region from about 13 microns to 8 microns (800cm-1 – 1300cm1)
Applications• Obtains Infrared spectrum of absorption,
emission, and photoconductivity of:– Solids, liquids and gases
• Identification of Cloud base temperatures
• Identification of inorganic compounds and organic compounds
• Measures solar irradiance• In Remote sensing
How the FTIR works• The FTIR spectrometer uses a Michelson
Interferometer setup that consists of:– A beam splitter, a fixed mirror, and a mirror
that translates back and forth.
Cold and hot black Bodies are for calibrationIn order to get correct cloud Radiance and BrightnessMeasurements.
Calibration
Thermistor Probe
Circulation Water Out
Circulation Water In
Cone
Black Paint
Calibration
• j
Detector
Cold Black Body
Hot Black Body
Mirror
Cold Black Body
0
0.002
0.004
0.006
0.008
0.01
0.012Cold Black Body Radiance
Wavenumber (cm-1)
Radi
ance
(Wm
/m2
Sr c
m-1
)
266.6266.7266.8266.9267
267.1267.2267.3267.4267.5267.6
Cold Black Body Brightness Temperature
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Entered Cold BBT: -6C
Generated Cold BBT: -5.9C
Hot Black Body
Entered Hot BBT: 44.16C
Generated Hot BBT: 44.19C
0.0000.0020.0040.0060.0080.0100.0120.0140.0160.0180.020 Hot Black Body Radiance
Wavenumber (cm-1)
Radi
ance
(Wm
/m2
Sr c
m-1
)
317317.05317.1
317.15317.2
317.25317.3
317.35317.4
317.45317.5
Hot Black Body Brightness Temperature
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Data CollectionRadiance:
H2O
Data CollectionBrightness Temperature:
• Cloud Base Temperatures• Comparing surface
temperature/moisture conditions
500.491670.207839.9231009.631179.341349.051518.751688.461858.160
50
100
150
200
250
300
350
Brightness Temperature
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
500.491 674.064 847.637 1021.21 1194.77 1368.33 1541.89 1715.45 1889.020
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
Radiance
Wavenumber (cm-1)
Radi
ance
(mW
/m2
Sr c
m-1
)
Cirrus- April 10, 17:00
.
Lidar Cloud height@ 1700: 5300m
Sounding LCLH@1700: 5610m
“Mostly Clear”- April 12, 1648
1510.070
0.002
0.004
0.006
0.008
0.01
0.012
0.014
Radiance
Wavenumber (cm-1)
Radi
ance
(mW
/m2S
r cm
-1)
1510.070
50
100
150
200
250
300
Brightness Temperatures
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Surface Temperature@ 1648: 9C
Sounding Surface Temp@ 1700: 10C
No significant clouds detected byThe Lidar for 1648.
Generally clear from 1645 to 1700
Altostratus- April 17, 16:36
1510.070
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
Radiance
Wavenumber (cm-1)
Radi
ance
(Wm
/m2
Sr cm
-1)
1510.07230
240
250
260
270
280
290
300
Brightness Temperature
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Base Cloud Temperature@ 1636: -15C
Sounding LCLT @ 1700: -11C
Compare the Cloud Height with theLidar and the Cloud temperature withThe brightness temperature
Lidar Cloud height@ 1636 : 4800mLidar Cloud height@ 1700: 4300m
Sounding LCLH@1700: 4400m
1510.07255
260
265
270
275
280
285
290
295
300
305
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Stratocumulus- April 19, 16:58
Cloud Base Temperature@ 1658: -2C
Sounding LCLT @ 1700: -1C
Brightness Temperature
1510.070
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
Radiance
Wavenumber (cm-1)
Radi
ance
(Wm
/m2
Sr c
m-1
)
Lidar Cloud height@ 1658 : 2400m
Sounding LCLH@1700: 3800m
1510.070
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
Clear Vs. Cloudy Ra-diance
Clear
Cloudy
Wavenumber (cm-1)
Radi
ance
(m
W/m
2Sr
cm-1
)
Lowered values of N2O
CH4 still present
Increased CO2
Increased H2O
Little to no CFC detection
No Ozone detection
1510.070
50
100
150
200
250
300
350
Clear Vs. Cloudy Brightness Temperatures
ClearCloudy
Wavenumber (cm-1)
Brig
htne
ss T
empe
ratu
re (K
)
Errors in Data• Cold and Hot black body
temperatures.• Quickly fluctuating hot and cold
black body temperatures.• Not a completely clear day for
comparison. • Sounding Location.
Conclusion• Evidence of stratospheric
greenhouse gases and surface gases.• Determine cloud base temperature
and height and compare with Lidar and sounding data.
• Further analyze unknown gases in data.
Questions?
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