Radiative Transfer Model

Vijay Natraj

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Why RADIANT?Why RADIANT?

The optical depth sensitivity of doublingThe optical depth sensitivity of doubling

The necessity of re-computing the entire RT The necessity of re-computing the entire RT solution if using a code such as DISORT if only solution if using a code such as DISORT if only a portion of the atmosphere changesa portion of the atmosphere changes

Goal: Employ the strengths of both while Goal: Employ the strengths of both while leaving the undesirable characteristics behindleaving the undesirable characteristics behind

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RADIANT: OverviewRADIANT: Overview

Plane-parallel, multi-stream RT modelPlane-parallel, multi-stream RT model

Allows for computation of radiances for user-defined Allows for computation of radiances for user-defined viewing anglesviewing angles

Includes effects of absorption, emission, and multiple Includes effects of absorption, emission, and multiple scatteringscattering

Can operate in a solar only, thermal only, or combined Can operate in a solar only, thermal only, or combined fashion for improved efficiencyfashion for improved efficiency

Allows stipulation of multiple phase functions due to Allows stipulation of multiple phase functions due to multiple constituents in individual layersmultiple constituents in individual layers

Allows stipulation of the surface reflectivity and surface Allows stipulation of the surface reflectivity and surface type (lambertian or non-lambertian)type (lambertian or non-lambertian)

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RADIANT: Solution MethodologyRADIANT: Solution Methodology

Convert solution of the RTE (a Convert solution of the RTE (a boundary value problem) into boundary value problem) into a initial value problem a initial value problem

Using the interaction principleUsing the interaction principle Applying the lower boundary Applying the lower boundary

condition for the scene at condition for the scene at handhand

Build individual layers (i.e. Build individual layers (i.e. determine their global determine their global scattering properties) via an scattering properties) via an eigenmatrix approacheigenmatrix approach

Combine layers of medium Combine layers of medium using adding to build one using adding to build one “super layer” describing “super layer” describing entire mediumentire medium

Apply the radiative input to Apply the radiative input to the current scene to obtain the current scene to obtain the RT solution for that scenethe 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: NormalOperational Modes: Normal

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Operational Modes: Layer SavingOperational Modes: Layer Saving

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Obtaining Radiances at TOAObtaining Radiances at TOA

I+(z*) = {T(0,z*)Rg[E-R(0,z*) Rg] -1T(z*,0)

+ R(z*,0) } I-(z*)

+ {T(0,z*)Rg[E-R(0,z*) Rg] –1R(0,z*)

+ T(0,z*)}agfoe-/o

+ T(0,z*)Rg[E-R(0,z*) Rg] –1S(z*,0)

+ S(0,z*)

RT Solution:

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Numerical Efficiency: Numerical Efficiency: Eigenmatrix vs. DoublingEigenmatrix vs. Doubling

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Numerical Efficiency: RADIANT vs. Numerical Efficiency: RADIANT vs. DISORTDISORT