Radiative Transfer Model Vijay Natraj

Welcome-2 Why RADIANT? The optical depth sensitivity of doubling 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 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 Goal: Employ the strengths of both while leaving the undesirable characteristics behind

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

Welcome-4 RADIANT: Solution Methodology Convert solution of the RTE (a boundary value problem) into a initial value problem Convert solution of the RTE (a boundary value problem) into a initial value problem Using the interaction principle Using the interaction principle Applying the lower boundary condition for the scene at hand Applying the lower boundary condition for the scene at hand Build individual layers (i.e. determine their global scattering properties) via an eigenmatrix approach 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 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 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) = R g I - (0) + a g f o e -  /  o

Welcome-5 Operational Modes: Normal

Welcome-6 Operational Modes: Layer Saving

Welcome-7 Obtaining Radiances at TOA I + (z*) = {T(0,z*)R g [E-R(0,z*) R g ] -1 T(z*,0) + R(z*,0) } I - (z*) + {T(0,z*)R g [E-R(0,z*) R g ] –1 R(0,z*) + T(0,z*)}a g f o e -  /  o + T(0,z*)R g [E-R(0,z*) R g ] –1 S(z*,0) + S(0,z*) RT Solution:

Welcome-8 Numerical Efficiency: Eigenmatrix vs. Doubling

Welcome-9 Numerical Efficiency: RADIANT vs. DISORT