1. 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.

3. Radiative Transfer Approximation

4. TRUTH and FAST models TRUTH FAST BACK END Monochromatic tables
Gases:
Line strengths/widths
e.g. HITRAN database
Surfaces:
Emissivity by land class and geometry
e.g. UCSB and P. Lucey tables
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
PRE-PROC
Parameterize and channel-weight
RT MODEL
Interpolate monochromatic data
TRUTH
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

5. Split atmosphere above cloud-top improves “TRUTH” accuracy (LBLDIS now at v1.7)
Need only execute DISORT to cloud top.
Separately compute monochromatic radiances and transmittances above cloud top with LBLRTM.
Interpolate DISORT output to LBLRTM TOA output resolution and compute “pseudo” monochromatic TOA radiances.
Spectrally reduce to hyperspectral instrument channels.

6. Comparison across entire band vs chirp

7. TOA Radiance Temperature RMSE
Improved consistency between FAST model R/T coefficients and verification model single scattering property tables leads to improvements in the RMSE radiance temperature differences

8. Surface emissivity and its impact

9. Aerosol Ensemble Optical Properties

10. UW GIFTS/HES CCH (clear, cloud, haze) Radiative Transfer Modeling

11. Next version ToDo List Solar radiation in the SMW band
Inclusion of aerosol effects on simulated TOA radiances