Minutes of the sixth International Radiative Transfer Workshop, June 2004

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BREDBECK  2004  Minutes
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Tuesday, 22/06/04
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9:30--10:00 Presentation for Cory Davis
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Modeling the effect of Cirrus on Microwave Limb sounder radiance
* introduction on EOS/MLS
* influence of the clouds on MLS measurements
* example of the simulation
* performance of the Monte Carlo method
  - error and CPU time depend on the ice path
  - randomly oriented particles are simpler to deal than the oriented particles 
* summary
Discussions:
AD: For the scattering properties: Do you use the Mischenko program?
CD: Mischenko constructed program. This is used only for the size
    distributions
PE: The shape does not matter so much
CM: Do you use Monte Carlo to have single scattering
    properties?


10:15 -- Franz Schreier
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* Spectral Grid Optimization Scheme for line-by-line cross section
* Definition for the cross section
* presentation of the algorithm: sample line center in a fine grid
* and coarser in the wings 
* use a function decomposition: smooth + rapid contribution
* Clough and Kneizys approach
* Uchiyama approach
* Performance of the 2 and 3 grid algorithm.
* examples of different schemes (for CO2)
* new scheme is much faster (scale of 10)
* Sparks scheme: performance (JQSRT 97)
* Conclusions: speed up of about a factor of 300
* Independent of the line shape
* Fair intercomparison with Sparks algorithm
SB: why the value of the cut off does not have influence on speed.
FS: the coarse grid is much larger then the fine one.   
SB: How do you subtract the line center?


11:15-- Claudia Emde
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Cloud contaminated mm-wave spectra using ARTS-1-1
* scattering model: presentation of the algorithm
* cloud-box definition
* discretisation of radiation field
* problems arisen: 
* sequential updated of the grid is required
* zenith angle grid optimization: more points around 90 deg (specially for
  limb sounder)
* presentation of the test cases setup
* 3D simulations-LOS: presentation of the results for different position of
  the sensor.
* difference of the 3D vs 1D. The results given by 1D are totally different.
* 3D model is strictly necessary.
Discussions:
A.D: Picard iteration to solve the radiative transfer equations
    Which are the boundary condition?
CE: compute the incoming radiation from all direction
PE: use one frequency and then use it as starting point
AD: Initial point important to reduce the number of iterations
CE: the first guess is not used for many points
AD, SB, PE,...: discussion on the boundary conditions and the way of
                implementation.


11:50-- Claas Teichmann
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Single scattering properties
* Definitions and set-up
* Example of the polarization difference field
* example of the effect of the gas absorption and scattering properties:
  changes only due to the gas absorption (for spherical particles)
* results similar for the cylindrical particles
* consistence check
* exemplification for the LOS inside the cloud
* more deformation at higher or lower aspect ratios
* strong differences in the signal for p20 and p30.
* for 500 GHz it does not work well (investigate)
* Summary and outlook

CM: What do you mean by sing scat. prop. change? Why does it depend on the
    gas absorption?
CT: discuss in the working group
CD: problem at 500GHz. Does it change with the aspect ratio?
CT: no, it is bad for all the aspect ratio.
CD: Ideas about what's going wrong?
CT: numerical problems..
CE: the idea is to calculate with Monte Carlo method and see if it is also
    a problem
PE: normalization problem?
SB:  advertising on the polarization working group
CM: Deformation ratio: how did you define it?
SB: publication from Georg Heygster on the single scattering properties


12:30: P.E., C.E., organization for the working group
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