1. A Unified Radiative Transfer Model: Microwave to Infrared
Tom Greenwald
CIMSS

2. Motivation
Why use one RT model across the thermal spectrum for multiple scattering calculations?
Physics is the same
Consistency in calculations
Reduces complexity in applications such as multi-sensor retrievals of atmospheric/cloud properties and direct radiance data assimilation
This presentation will examine monochromatic adjoint sensitivities and contrast them in clear sky and cloudy conditions

3. Description of Modeling System
Multiple scattering RT model: Successive Order of Interaction (SOI) method (Heidinger et al. 2005; O’Dell et al. 2005)
Fast and accurate (< 1 K over most conditions)
Can accommodate any number of cloud layers
Adaptive: variable number of streams (angular resolution). Other fast models do not have this flexibility since angular resolution is fixed
Incorporated into CRTM and tested
LBL gas absorption models:
Infrared: LBLRTM v8.4
Microwave: Liebe MPM v. 1989

4. Description of Modeling System contd.
Cloud single-scattering properties:
Infrared: Tables of properties for mixture of habits (Baum et al. 2005) and individual habits (bullet rosettes, columns, plates, aggregates) based on rigorous techniques (Yang); water spheres based on Anomalous Diffraction Theory
Microwave: Tables of properties for bullet rosettes, plates, columns and ice spheres based on DDA calculations (Evans)
Adjoint models built for all forward models except LBLRTM

5. Experimental Setup Tropical mean temperature/humidity profiles
Cloud properties

6. Experimental Setup contd.
Surface properties
Microwave emissivity: Fresnel equation; permittivity model from Stogryn et al. (1995)
Infrared emissivity: Fixed 0.98
Geometry
Zenith angle = 0o

7. Forward Results

8. Adjoint Sensitivity Analysis
Jacobian
Adjoint forcing
• Definition of adjoint:
• Forward vs. adjoint sensitivity: Adjoint is much faster and gives more accurate derivatives
• Non-dimensional relative sensitivity (Zou et al. 1993):

9. Non-dimensional Tb Sensitivity to Atmospheric Temperature (Thermal Source only)
Clear
sky
Cloudy

10. Non-dimensional Tb Sensitivity to Water Vapor Mixing Ratio
Clear
sky
Cloudy

11. Absolute Tb Sensitivity to Water Vapor Mixing Ratio (K/g/kg)
Clear
sky
Cloudy

12. Non-dimensional Tb Sensitivity to LWP and IWP

13. Summary Additional near-term work:
An example of the capabilities of a unified RT modeling system was given and illustrated the complementary nature of information on the atmosphere and clouds in the microwave and IR
Additional near-term work:
Compare various techniques for handling gas absorption and scattering across spectral bands (e.g., k-distribution method and Optimal Spectral Sampling)
Explore and further develop approximate physical methods (e.g., Anomalous Diffraction Theory) for fast computation of scattering properties