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Radiative Transfer Model

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Title: PowerPoint Presentation Author: dcrisp Last modified by: Vij Created Date: 5/2/2002 2:05:26 AM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

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Title: Radiative Transfer Model


1
Radiative Transfer Model Vijay Natraj
2
Why RADIANT?
  • The optical depth sensitivity of doubling
  • The necessity of re-computing the entire RT
    solution if using a code such as DISORT if only a
    portion of the atmosphere changes
  • Goal Employ the strengths of both while leaving
    the undesirable characteristics behind

3
RADIANT Overview
  • Plane-parallel, multi-stream RT model
  • Allows for computation of radiances for
    user-defined viewing angles
  • Includes effects of absorption, emission, and
    multiple scattering
  • Can operate in a solar only, thermal only, or
    combined fashion for improved efficiency
  • Allows stipulation of multiple phase functions
    due to multiple constituents in individual layers
  • Allows stipulation of the surface reflectivity
    and surface type (lambertian or non-lambertian)

4
RADIANT Solution Methodology
  • Convert solution of the RTE (a boundary value
    problem) into a initial value problem
  • Using the interaction principle
  • Applying the lower boundary condition for the
    scene at hand
  • Build individual layers (i.e. determine their
    global scattering properties) via an eigenmatrix
    approach
  • Combine layers of medium using adding to build
    one super layer describing entire medium
  • Apply the radiative input to the current scene to
    obtain the RT solution for that scene

The Interaction Principle
I(H) T(0,H)I(0) R(H,0)I-(H) S(0,H)
Lower Boundary Condition I(0) RgI-(0)
agfoe-?/?o
5
Operational Modes Normal
6
Operational Modes Layer Saving
7
Obtaining Radiances at TOA
RT Solution
I(z) T(0,z)RgE-R(0,z) Rg -1T(z,0)
R(z,0) I-(z)
T(0,z)RgE-R(0,z) Rg 1R(0,z)
T(0,z)agfoe-?/?o
T(0,z)RgE-R(0,z) Rg 1S(z,0)
S(0,z)
8
Numerical Efficiency Eigenmatrix vs. Doubling
9
Numerical Efficiency RADIANT vs. DISORT
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