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?