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Radiant 2.0: An Introduction

Radiant 2.0: An Introduction. Mick Christi OCO Science Meeting March 2004. Why Another Radiative Transfer Solver?. Wide use of (1) Doubling & Adding and (2) DISORT. The Problem. The optical depth sensitivity of doubling.

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Radiant 2.0: An Introduction

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  1. Radiant 2.0:An Introduction Mick Christi OCO Science Meeting March 2004

  2. Why Another Radiative Transfer Solver? Wide use of (1) Doubling & Adding and (2) DISORT

  3. The Problem • 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. • Our Goal: Employ the strengths of both while leaving the undesirable characteristics behind.

  4. Radiant Overview • Plane-parallel, multi-stream RT model. • Can compute either radiances or spectral radiances as appropriate. • 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. Capability to surgically select delta-m scaling as needed by the user for those constituents. • Allows stipulation of the surface reflectivity and surface type (lambertian or non-lambertian). Simulating Radiative Processes

  5. Radiant Overview • Incorporates layer-saving to greatly improve efficiency when the computation of Jacobians by finite difference is required. • Accuracy tested against established tables and codes (e.g. van de Hulst (1980), doubling codes, and DISORT). • Speed tested against doubling codes and DISORT with encouraging results. Simulating Radiative Processes

  6. RTE Solution Methodology employed in Radiant • 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) I-(0) = T(H,0)I-(H) + R(0,H)I+(0) + S(H,0) Lower Boundary Condition: I+(0) = RgI-(0) + agfoe-/o

  7. Operational Modes:Normal Mode

  8. Operational Modes:Layer-Saving Mode

  9. Obtaining Radiances at the 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] –1S(z*,0) + S(0,z*) I-(z*) R(0,z*) I+(z*) z* RT Solution: S(0,z*) 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*) T(z*,0) T(0,z*) S(z*,0) 0 I-(0) R(z*,0) I+(0)

  10. Numerical Efficiency:Eigenmatrix vs. Doubling

  11. Numerical Efficiency:Radiant vs. DISORT

  12. Radiant: Program Structure • Subroutines: • DATA_INSPECTOR – Input Data Checker • PLKAVG – Integrated Planck • PLANCK – Monochromatic Planck • RAD – Computes radiances for normal & layer-saving modes • Singularity Busting: • o = 1 •  = o or  = i

  13. Radiant: Program Structure • Subroutines • BUILD_LAYER - Determines global scattering properties of layer being built • COMBINE* - Combines Global Transmission, Reflection, & Source Matrices • SURF* - Surface Depiction: • 1_3 (Lambertian) • 2_2 (Non-lambertian) • Layer-Saving – Global Transmission, Reflection, & Sources for each layer (& atmospheric block) saved for later use

  14. Radiant: Program Structure • Subroutines: • LOCAL – Determines local (i.e. intrinsic) scattering properties of layer being built • SGEEVX – Solves the eigenvalue problem to use in determination of global scattering properties

  15. Radiant: Program Structure • Subroutines: • GETQUAD2 – Provides Lobatto, Gauss, or Double Gauss quadrature parameters • PLEG – Provides legendre polynomial information for computation of constituent phase functions

  16. Summary • Radiant developed in response to some weaknesses in doubling & adding and in the discrete ordinate method as implemented by DISORT. • Radiant employs “eigenmatrix & adding”. • The method allows Radiant to obtain an accurate RT solution that can be much more efficient depending on the problem at hand.

  17. Your Questions& Comments

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