Developement of exact radiative transfer methods Andreas Macke, Lüder von Bremen, Mario Schewski Institut für Meereskunde, Uni Kiel

Introduction ❑ Monte Carlo method exactly simulates radiative transfer prosesses in arbitrary complex scattering and absorbing media (clouds) ❑ Numerical application feasible for ❑ local and domain average ❑ fluxes and radiance fields at specified layers ❑ Full 3D radiance fields  SHDOM (not exact)

Complete MC package (GRIMALDI) ❑ forward scheme to solve radiative transfer in 3d scattering and absorbing atmosphere with directed (solar) illumination ❑ preprocessor for absorption properties of atmospheric gases ❑ monochromatic and spectral band fluxes and radiances for finite sized angular bins ❑ photon path length pdf for finite sized angular bins ❑ data base for scattering phase functions and single scattering albedos for spherical and non-spherical cloud particles

Forward Local Estimate MC (MC-UNIK) ❑ forward scheme to solve radiative transfer in 3d scattering and absorbing atmosphere with directed (solar) illumination ❑ monochromatic fluxes and radiances for discrete directions (Local Estimate scheme) ❑ data base for scattering phase functions and single scattering albedos for spherical and non-spherical cloud particles

Backward Local Estimate MC (MC-UNIK-BW) ❑ backward scheme to solve radiative transfer in 3d scattering and absorbing atmosphere with directed (solar) illumination ❑ monochromatic radiances for discrete directions (Local Estimate scheme) ❑ photon pathlength pdf for predefined viewing geometries and viewing locations ❑ data base for scattering phase functions and single scattering albedos for spherical and non-spherical cloud particles

Backward MC (3RAD-UNIK) ❑ backward scheme to solve radiative transfer in 3d scattering, absorbing and emitting atmosphere ❑ monochromatic radiances for discrete directions ❑ preprocessor for gas absorption from the thermal to the microwave ❑ data base for scattering phase functions and single scattering albedos for spherical cloud particles

Internet  Programs & Tools

Remote Sensing of inhomogeneous clouds - vertical structure, photon path length - Steffen Meyer, Mario Schewski, Andreas Macke Institut für Meereskunde, Uni Kiel

Problem - cloud variability breaks unique cloud-radiance relation -

MC-Local Estimate - discrete directions, spatial weighting function - ❑ Initialisation: ❑ scattering phase function ❑ single scattering albedo  0 ❑ vol. extinction coefficient  x ❑ detector position (  ) ❑ output: ❑ reflected radiances L ❑ weighting function of L (x,y,z)

artificial vertical cloud profiles ❑ local variations of cloud extinction coefficient with preseved optical thickness

settings ❑  = 10, 20, 40 ❑ = 0.625; 0.850; 1.000; 1.600;  m ❑ r eff = 16  m; variable ❑ surface albedo  = 0.0 ❑ geometries: ❑ sun:   = 60 0 ;  0 = 0 0 ❑ satellite:  =0 0 ;  =0 0 (nadir)

constant profile (  =10; r eff =16  m)

linear profile (  =10; r eff =16  m)

constant profile (  =10; r eff =var)

constant profile (  =40; r eff =16  m)

linear profile (  =40; r eff =16  m)

dependency of penetration depth on absorption single scattering albedo  0 wavelength [  m] single scattering albdo

spectral variation of scattering phase function and single scattering albedo cloud profile spectral weighting function

spectral variation of extinction coefficient percent of incoming radiation absorbed [  m]  m  m  m  m

settings ❑ = [0.9, 1.0, 0.025]  m (b1) [1.4, 1.5, 0.025]  m (b2) [1.95, 2.2, 0.025]  m (b3) [2.8, 3.0, 0.025]  m (b4) ❑  = 10.8 ❑ r eff = proportional to extinction coefficient ❑ surface albedo  = 0.0 ❑ geometries: ❑ sun:   = 60 0 ;   = 0 0 ❑ satellite:  =0 0 ;  =0 0 (nadir)

Weighting function for gaussian profile of ext. coeff. and particle size (  =10.8; Q ext = 2.0)

extinction efficiency - size and wavelength dependency -

Weighting function for gaussian profile of ext. coeff. and particle size (  =10.8; Q ext = f(, r eff ))

Simulation of photon pathlength distributions - backward Monte Carlo for solar radiative transfer - ❑ Initialisation: ❑ scattering phase function ❑ single scattering albedo  0 ❑ vol. extinction coefficient  x ❑ detector position (  ) ❑ detector location (x,y) ❑ output: ❑ transmitted radiances L ❑ photon pathlength distributions

example cloud

photon pathlength pdf

Summary and outlook ❑ MC methods developed, validated and made public available ❑ profiling of vertical cloud structure at solar wavelengths not feasible ❑ backward MC at solar wavelengths developed and validated ❑ photon pathlength pdf in progress ❑ simulation of radiance power spectra as a function of vertical and horizontal cloud variability ❑ more detailed consideration of cloud microphysical properties

The Future ❑ Proposal for a new research activity in support of 4DCLOUDS (year 4 & 5) ❑ cloud resolving models (dynamical, statistical) with explicit cloud microphysics as data base for cloud-radiation correlation

Correlation between domain averaged fluxes and cloud fields (parameterisation?)

Radiative transfer calculations ❑ Radiative fluxes calculated with MC-forward modell GRIMALDI ❑ Scattering and absorption at atmospheric gases and cloud particles ❑ 756 GESIMA clouds ❑ 52 x 52 x 26 grid boxes ❑ 2 km horizontal resolution ❑ 100 m – 1 km vertical resolution  10 km domain height ❑ 9 solar zenith angles (0°, 10°... 80°) ❑ 13 spectral bands

Spectral intervals

Scattering phase functions

Parameterization ❑ Multiple regression ❑ Nonlinear dependencies between cloud-parameters and radiative fluxes

Best fitting cloud parameters Cloud parameters used to obtain the individual radiative properties at solar zenith angle  0 = 50°:

Dependency on solar zenith angle

The End!

vertikale Profile GESIMA Wolke 'Issig' Wolke idealisierte Wolke

homogene Wolke (  =67.21)

Gauss-Wolke (  =1.0;  =100.0 ) r eff =1.0

Gauss-Wolke (  =1.0; ) r eff =10.0

GESIMA (  =19.25)  = 0.0  = 0.06

'Issig' Wolke

Gauss-Wolken (  =1.0; 100.0)(detector=bottom)

GESIMA (  =19.25) (detector=bottom)

Zusammenfassung I ❑ reflektierte Strahldichte am Satelliten stammt aus oberen Wolkenschichten ❑ Berücksichtigung versch. Wellenlängen führt zu keinem Gewinn an Information ❑ auch mit bodengebundener Fernerkundung keine Information über Profil

effektiver Radius Extinktionskoeffizient optische Dicke

Gauss-Issig (  =272)  = 0.06  = 0.0  = 0.8

Gauss-Wolken (detector=bottom)

reste  = Grass ?

'Issig' Wolke (detector=bottom)

Doppelschichtwolke