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Modelling polarized microwave radiation in a 3D spherical cloudy

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Modelling polarized microwave radiation in a 3D spherical cloudy Powered By Docstoc
					Modelling polarized microwave radiation in a 3D
         spherical cloudy atmosphere

                        Claudia Emde
                                                             iup
                                 u
                        Stefan B¨hler
                       Patrick Eriksson
                        Oliver Lemke
                       Sreerekha T.R.



             EGS-AGU-EUG Joint Assembly
                  April 06-11, 2003
                    Nice, France




              ARTS - Atmospheric Radiative Transfer System         EGS 2003, Nice
                                     Contents


• Model atmosphere and cloudbox

• Concept of ARTS (Atmospheric Radiative Transfer System)

• Single scattering database

• Radiative transfer in cloudbox
  ⇒ successive order of scattering method

• First results

• Conclusions and outlook




                        ARTS - Atmospheric Radiative Transfer System   EGS 2003, Nice
                           Model atmosphere


• 3D:
 – Spherical coordinate system (pressure, latitude, longitude)
 – Realistic simulations (strongly inhomogeneous cloud coverage)

• 1D:
 – Spherically symmetric atmosphere (only pressure coordinate).
 – Estimation of upper limit of scattering effects.
 – Much faster computation than 3D.

• 2D:
 – Atmosphere extends inside plane (polar coordinate system).
 – Application: Satellite measurements (Observation inside orbit plane).
 – Scattering calculations impractical.




                       ARTS - Atmospheric Radiative Transfer System        EGS 2003, Nice
                     Cloudbox - scattering domain



     ATMOSPHERE
                                              CLOUDBOX


                                                                            Scattered radiation field
                                                                            is calculated inside the
                                                                            cloudbox using
                                                                            successive order of
                        EARTH
                                                                            scattering approach.


Definition of cloudbox:
• corner points ⇔ atmospheric grid points

• 3D atmosphere:
  [p1, p2, α1, α2, β1, β2]


                             ARTS - Atmospheric Radiative Transfer System                   EGS 2003, Nice
                              The concept of ARTS

  Single Scattering Database                           Spectral Line Catalogue
                                                                 HITRAN
            Extinction Matrix                                      JPL
               Phase Matrix                             Gas species: H2O, O2, N2, ...
           Absorption Vector
   Particle Types: Spheres, Cylinders ...
Distribution types: Gamma, Log Normal, ...
                                                              Gas Absorption
                                                               Lookup Table
                          Propagation path
                             calculation



                                                            Clearsky Radiative
Radiative transfer in cloudbox                                   Transfer
     Solution of Vector RT equation                     Solution of Vector RT equation

Successive order of scattering approach                     Exponential approach
          (Iterative Method)                                  Stokes vector for a
                                                               propagation path
      Radiation field in cloudbox




                                          Simulated Sensor Spectrum


                            ARTS - Atmospheric Radiative Transfer System                 EGS 2003, Nice
                      Single Scattering Database




• Hydro-meteor species defined by
  – Phase matrix
  – Extinction matrix
  – Absorption vector

• One species can be ensemble or single particle.

• T-matrix method for computation (Mishchenko code).

• Data format: XML




                        ARTS - Atmospheric Radiative Transfer System   EGS 2003, Nice
                    Vector radiative transfer equation


      dI
         (n, ν) = −K(n, ν)I(n, ν) + a(n, ν)B(ν) +                            dn Y(n, n , ν)I(n , ν)
      ds                                                                4π




I = (I, Q, U, V )                  Stokes Vector
               n     propagation direction of the radiation
               ν                      frequency
               K         extinction coefficient matrix
               a         absorption coefficient vector
              B                  Planck function
               Y                   phase matrix




                         ARTS - Atmospheric Radiative Transfer System                         EGS 2003, Nice
                   Successive order of scattering method



   First Guess Field                    Old Radiation Field                      copy
Interpolated clearsky field

                                                                                               no


                     Scattering Integral
                                                                Convergence Test
                                                                                               yes



                       solve VRTE
                    Exponential Approach
                                                                                  Solution Field
                                                                             Radiation field in cloudbox




                                         New Radiation Field



                              ARTS - Atmospheric Radiative Transfer System                   EGS 2003, Nice
            1D test calculations for a homogeneous cloud

   Setup:

• 1D atmosphere.

• Cloudbox from 360 hPa to 280 hPa.

• 12 pressure levels.

• Spherical ice particles, radius 200 µm

• Constant particle number density: 1297 m−3

• Absorption from lookup table for the species: H2O, O3, O2, N2

• Frequencies:
  – 318 GHz: Case for low absorption.
  – 322 GHz: Case for medium absorption.
  – 324 GHz: Case for high absorption.

                        ARTS - Atmospheric Radiative Transfer System   EGS 2003, Nice
                                                            Calculation for three frequencies

                                                                    1. Stokes component


           Brightness Temperature Difference [ K ]
                                                      40
                                                                                                    318 GHz
                                                                                                    322 GHz
                                                      30
                                                                                                    324 GHz

                                                      20


                                                      10


                                                       0


                                                     −10
                                                        0      50            100          150                  200
                                                                     Zenith Angle [ deg ]

                         2. Stokes component
Difference between clearsky field and scattered field for three
    erature Difference [ K ]




        0.2
test cases.
                                               318 GHz
Radiation field for all viewing directions at the bottom of the
                                               322 GHz
cloud.                                         324 GHz


                                                       0
                                                                ARTS - Atmospheric Radiative Transfer System         EGS 2003, Nice
                                         Convergence behaviour

                                 Zenith angle:56 [deg]
                   260
                                                                                   clearsky
                                                                                   initial
                   270
                                                                                   iteration1
                                                                                   iteration2
                   280                                                             iteration3
                                                                                   iteration4
                   290                                                             solution5
Pressure [ hPa ]




                   300
                                                                                Clearsky field, initial field and
                   310                                                          iterations for the intensity (I) at
                                                                                318 GHz as a function of altitude
                   320
                                                                                for a fixed viewing direction of
                   330                                                          56◦.

                   340

                   350
                      2   4         6      8     10       12            14
                              Brightness Temperature [ K ]

                                         ARTS - Atmospheric Radiative Transfer System                    EGS 2003, Nice
                                      Summary


• Scattering calculations performed for 1D and 3D test cases.
  ⇒ Reasonable results.

• Successive order of scattering method implemented for solving VRTE.

• Polarized and unpolarized radiation fields can be simulated.

• T-matrix method selected for calculating single scattering properties.

• Geometrical propagation path calculations implemented for 1D, 2D and 3D;
  with and without refraction.




                         ARTS - Atmospheric Radiative Transfer System      EGS 2003, Nice
                                     Outlook


• Main problem: Using all implemented features at the same time requires long
  computation time and large working memory.

• Optimizations (e.g. improved first guess field) planned to be implemented.




More information availabe on web-page:

   http://www.sat.uni-bremen.de/arts/




                       ARTS - Atmospheric Radiative Transfer System     EGS 2003, Nice

				
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