Determination of atmospheric temperature, water vapor, and heating rates from mid- and far- infrared hyperspectral measurements

1
Determination of atmospheric temperature, water
vapor, and heating rates from mid- and far-
infrared hyperspectral measurements

• AGU Fall Meeting, Wednesday, December 12, 2007
• GC34A-02
• D.R. Feldman (Caltech)
• K.N. Liou (UCLA) Y.L. Yung (Caltech)
• D. G. Johnson (LaRC) M. L. Mlynczak (LaRC)

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Presentation Outline

• Motivation for studying the far-infrared
• FIRST instrument description
• Sensitivity tests of mid-IR vs far-IR
  capabilities
• Clear-sky
• Cloudy-sky
• Multi-instrument data comparison
• Climate model considerations
• Conclusions

• Outline

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The Far-Infrared Frontier

• Current EOS A-Train measure 3.4 to 15 µm, dont
  measure 15-100 µm
• IRIS-D measured to 25 µm in 1970
• Far-IR, through H2O rotational band, affects OLR,
  tropospheric cooling rates
• Far-IR processes inferred from other spectral
  regions
• Mid-IR, Microwave, Vis/NIR
• Interaction between UT H2O and cirrus clouds
  requires knowledge of both
• Currently inferred from measurements in other
  spectral regions

No spectral measurements to the right of line
Figures derived from Mlynczak et al, SPIE, 2002

• Motivation

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FIRST Far Infrared Spectroscopy of the
Troposphere

• FTS w/ 0.6 cm-1 unapodized resolution, 0.8 cm
  scan length
• Multilayer beamsplitter
• Germanium on polypropylene
• Good performance over broad spectral ranges in
  the far-infrared
• 5-200 µm (50 2000 cm-1) spectral range
• NeDT goal 0.2 K (10-60 µm), 0.5 K (60-100 µm)
• 10 km IFOV, 10 multiplexed detectors
• Cooling
• Spectrometer LN2 cooled
• Detectors liquid He cooled
• Scan time 1.4-8.5 sec
• Balloon-borne ground-based observations

• FIRST instrument

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Retrieval Sensitivity TestFlow Chart
Random Perturbations
Model Atmosphere
A priori Atmospheric State)
RTM
RTM Noise
A priori uncertainty
A priori spectrum
Synthetic Measurement
Retrieval algorithm
Analyze retrieved state, spectra, and associated
statistics

• Sensitivity tests

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Clear-Sky Retrieval Test

• AIRS and FIRST T(z) retrievals comparable.
• FIRST better than AIRS in H2O(z) retrievals
  200-300 mbar.
• Residual signal in far IR seen 100-200 cm-1 ?
  low NeDT critical

• Sensitivity tests

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Clear-Sky Heating Rates
Tropical Conditions
Sub-Artic Winter Conditions

• Spectra provide information about fluxes/heating
  rates
• Error propagation (Taylor et al, 1994 Feldman et
  al, In Review) can be used
• Heating rate error for scenes with clouds
  generally higher due to lack of vertical cloud
  information

• Heating Rates

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Extrapolating Far-IR with Clouds

• Retrieval of T(z), H2O(z), CWC(z), CER(z)
  difficult with AIRS spectra
• Use AIRS channels to extrapolate far-IR channels?
• Depends on cloud conditions, T(Z), H2O(z)
• Low BT channels from 6.3 µm band low BT
  channels in far-IR
• High BT channels scale from mid- to far-IR
• For tropics, channels with BT 250-270 K (emitting
  5-8 km) are complicated

• Clouds

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Test Flight on September 18, 2006Ft, Sumner NM
AQUA MODIS L1B RGB Image
AIRS Footprints
FIRST Balloon
CloudSat/CALIPSO Track

• Test flight

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CloudSat/CALIPSO signals

• CloudSat and CALIPSO near collocation
• No signal from CloudSat
• CALIPSO signal consistent with FIRST residual

• Test flight

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FIRST and AIRS Cloud Signatures

• Instrument collocation
• FIRST balloon-borne spectra
• AIRS
• MODIS
• Residuals are consistent with clouds 5 km, De
  60 µm

Cloud Detected !

• Test flight

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Climate Model Considerations

• Climate models produce fields that specify mid-
  far-IR spectra.
• Multi-moment statistical comparisons of measured
  spectra and modeled spectra avoid subtle biases
  from data processing.
• Spectral and atmospheric state spaces should be
  considered jointly.
• Far-IR climate model analysis requires more
  far-IR data
• Far-IR extrapolation should retain physical basis
  and be verified with measurements.
• Agreement with CERES is only partial verification
  and presents a non-unique checksum
• Future work to assess how spectra impart
  information towards climate model processes.

• Model evaluation

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Conclusions

• AIRS measures mid-IR, but far-IR is not covered
  A-Train spectrometers.
• FIRST provides thorough description of far-IR but
  limited spectra are available.
• FIRST clear-sky T retrievals comparable, improved
  UT H2O retrieval relative to AIRS
• Implied cooling rate information difference is
  small .
• Extrapolating far-IR channels good for Tb 220
  K, ok for Tb 300 K, difficult for Tb 250-270
  K.
• Multi-instrument analysis with A-Train
  facilitates comprehensive understanding of FIRST
  test flight spectra.
• AIRS mid-IR spectra can validate climate models,
  but far-IR should not be neglected.

• Conclusions

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Acknowledgements

• NASA Earth Systems Science Fellowship, grant
  number NNG05GP90H.
• Yuk Yung Radiation Group Jack Margolis, Vijay
  Natraj, King-Fai Li, Kuai Le
• George Aumann and Duane Waliser from JPL
• Xianglei Huang from U. Michigan and Yi Huang
  from Princeton
• AIRS, CloudSat, and CALIPSO Data Processing Teams

• Thank you for your time

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Cloud Radiative Effect (CRE)

• CRE TOA clear broadband flux TOA broadband
  flux
• CERES provides collocated measurements of CRE
  from broadband radiometers
• Most CERES products contain multiple data-streams
• AIRS L3 CRE lower than CERES CRE
• Other A-Train sets (CloudSat/CALIPSO) can
  arbitrate difference

• Clouds

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Towards CLARREO

• NRC Decadal Survey recommended CLARREO for
• Radiance calibration
• Climate monitoring
• CLARREO specified to cover 200 2000 cm-1 with lt
  2 cm-1 resolution
• NIST traceability requirement
• Prototyped far-IR instruments provide a science
  and engineering test-bed for next generation of
  satellite instruments
• Further orbital simulations required to test how
  mid-IR state space uncertainties appear as far-IR
  spectral residuals
• More integrated A-train analyses w.r.t. Far-IR
  warranted
• Larger Far-IR dataset analysis needed to
  demonstrate utility of long wavelength
  measurements for climate monitoring
• Dont forget about 50-200 cm-1 (200-50 µm).

• Future directions