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Radiative Transfer Model Vijay Natraj

Radiative Transfer Model Vijay Natraj. 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

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Radiative Transfer Model Vijay Natraj

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  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*)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*)

  8. Numerical Efficiency: Eigenmatrix vs. Doubling

  9. Numerical Efficiency: RADIANT vs. DISORT

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