Radiative Transfer Model

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Radiative Transfer Model Vijay Natraj
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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

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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)

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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
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Operational Modes Normal
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Operational Modes Layer Saving
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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)
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Numerical Efficiency Eigenmatrix vs. Doubling
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Numerical Efficiency RADIANT vs. DISORT