The GIFTS Fast Model: Clouds, Aerosols, Surface Emissivity

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The GIFTS Fast Model Clouds, Aerosols, Surface
Emissivity

• James E. Davies
• ABSTRACT
• The GIFTS fast radiative transfer model is
  evolving to include the radiative effects of
  clouds, aerosols and surface spectral emissivity.
  It does have some complexity, mainly in the
  domain of user choices (fixed ? spectral ?
  representative of land (or ocean) class randomly
  or geographically selected angular dependence).
  Once provided with an interface to these choices,
  and, where applicable, alternate processing paths
  in the fast radiative transfer code, the next
  task is to ensure that the verification code (by
  which the fidelity of the fast model is judged)
  has sufficient flexibility to test the fast
  model. The same general issues arise with clouds
  and aerosols.
• This presentation gives an update on the status
  of the GIFTS fast model and foreshadows some of
  the challenges ahead.

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http//www.ssec.wisc.edu/gifts/noaa/
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Radiative Transfer Approximation
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TRUTH and FAST models
BACK END
Monochromatic tables
Gases Line strengths/widths e.g. HITRAN database
Clouds Single scattering properties by crystal
habit and size dist. e.g. LBLDIS tables
Aerosols Single scattering properties by
mineral and size dist. e.g. I. Sokolik tables
Surfaces Emissivity by land class and
geometry e.g. UCSB and P. Lucey tables
PRE-PROC
Parameterize and channel-weight
Interpolate monochromatic data TRUTH
RT MODEL
FAST
POST-PROC
Apply instrument effects (spectral and spatial
integration)
FRONT END
TRUTH Radiances For selected instrument
channels
FAST Radiances For all instrument channels
Channel Radiances
Channel Radiances
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Split atmosphere above cloud-top improves TRUTH
accuracy (LBLDIS now at v1.7)

1. Need only execute DISORT to cloud top.
2. Separately compute monochromatic radiances and
   transmittances above cloud top with LBLRTM.
3. Interpolate DISORT output to LBLRTM TOA output
   resolution and compute pseudo monochromatic TOA
   radiances.
4. Spectrally reduce to hyperspectral instrument
   channels.

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Comparison across entire band vs chirp
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TOA Radiance Temperature RMSE
Improved consistency between FAST model R/T
coefficientsand verification model single
scattering property tables leadsto improvements
in the RMSE radiance temperature differences
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Surface emissivity and its impact
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Aerosol Ensemble Optical Properties
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UW GIFTS/HES CCH (clear, cloud, haze) Radiative
Transfer Modeling
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Next version ToDo List

1. Solar radiation in the SMW band
2. Inclusion of aerosol effects on simulated TOA
   radiances