International Polarized Radiative Transfer

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====== IPRT polarized radiative transfer model intercomparison ======

==== General conventions: ====
 
  * For all cases normalized radiances are compared (i.e. Stokes vector components devided by the extraterrestrial irradiance). 
  * The viewing azimuth angle is defined clockwise
  * The sun position is the position of the sun in the sky defined by solar zenith angle sza and solar azimuth angle saa. Note that the direction vector (vza, vaa) is then opposite to the solar beam travel direction (vaa = saa indicates that the sensor looks into the direction of the sun, vaa-saa = 180° means that the sun is in the back of the sensor)
  * The output format is ascii, details are provided for the individual test cases

In order to check model definitions of signs of the Stokes vector and azimuth angles, you should first run only case A1.  

==== Phase I - One-dimensional test cases ====

=== A - Test cases with one layer ===
  - [[intercomparisons:a1_rayleigh|Rayleigh scattering]]
  - [[intercomparisons:a2_lambert|Lambertian surface]]
  - [[intercomparisons:a3_aerosol_spherical|Spherical aerosol particles]]
  - [[intercomparisons:a4_aerosol_spheroid|Spheroidal aerosol particles]]
  - [[intercomparisons:a5_water_cloud|Liquid water cloud]]
  - [[intercomparisons:a6_ocean1|Ocean surface]]

=== B - Test cases with multi-layers ===
  - [[intercomparisons:b1_rayleigh|Rayleigh scattering, standard atmosphere]]
  - [[intercomparisons:b2_absorption|Rayleigh scattering and molecular absorption, standard atmosphere]]
  - [[intercomparisons:b3_aerosol|Aerosol profile]]
  - [[intercomparisons:b4_cloud_ocean|Cloud above ocean surface]]

**Publication:**
C. Emde, V. Barlakas, C. Cornet, F. Evans, S. Korkin, Y. Ota, L. C.-Labonnote, A. Lyapustin, A. Macke, B. Mayer, and M. Wendisch. //IPRT polarized radiative transfer model intercomparison project – phase A.// J. Quant. Spectrosc. Radiat. Transfer, 164(0):8-36, 2015. [[http://www.sciencedirect.com/science/article/pii/S0022407315001922|link]]

==== Phase II - Three-dimensional cases ====

  - [[intercomparisons:c1_stepcloud|Step cloud]]
  - [[intercomparisons:c2_cubiccloud|Cubic cloud]]
  - [[intercomparisons:c3_cumulus|Cumulus cloud]]	

**Publication:**
C. Emde, V. Barlakas, C. Cornet, F. Evans, Z. Wang, L. C.-Labonotte, A. Macke, B. Mayer, and M. Wendisch. //IPRT polarized radiative transfer model intercomparison project – three-dimensional test cases (phase B).// J. Quant. Spectrosc. Radiat. Transfer, 209:19-44, 2018.[[https://www.sciencedirect.com/science/article/pii/S0022407317308981|link]] 

==== Phase III - 1D spherical geometry ====

=== General conventions and settings ===
     
{{ :intercomparisons:phase_d:spherical_system.png?400 |Figure from Gao et al. 2023, https://doi.org/10.5194/amt-16-5863-2023}}

  * Definition of angles for all simulations in spherical geometry: We refer to the **angles at the position of the observer**, i.e. at the top of the atmosphere VZA=θ<sub>v</sub>' and SZA=θ<sub>0</sub>'. For the observer at the surface VZA=θ<sub>v</sub> and SZA=θ<sub>0</sub>. The azimuth angles also  refer to the position of the observer. The figure is taken from [[https://doi.org/10.5194/amt-16-5863-2023|Gao et al. 2023]].        

  * Results should be provided as **normalized radiances** (i.e. Stokes vector components divided by the extraterrestrial irradiance).
  
  * For all cases except E6, the same **sun-observer geometries** should be calculated:
      * //viewing zenith angles// (deg): [0, 9, 18, 26, 34, 41, 48, 54, 60, 65, 70, 74, 78, 81, 84, 86, 88, 89, 90] (up-looking at bottom of atmosphere, down-looking at top of atmosphere]
      * //viewing azimuth angles// (deg): 0-180, 10° increment 
      * //solar zenith angles// (deg): [30, 60, 80, 87, 90, 93, 96, 99]
      * //solar azimuth angle// (deg): 0
      * //sensor altitudes// (km): 0, 120

  * The **output format is netcdf**, results of all cases (D and E) shall be included in a single netcdf file using {{:intercomparisons:phase_d:iprt_phase3_model.nc|iprt_phase3_XXX.nc}} as template. Please include normalized radiance and the standard deviation (if you calculate it) for each case:
      - radiance_//case//(//case//_zout, //case//_sza, //case//_saa, //case//_vza, //case//_vaa, stokes)  
      - std_//case//(//case//_zout, //case//_sza, //case//_saa, //case//_vza, //case//_vaa, stokes)
    

=== D - Test cases for fully spherical geometry with one layer ===

  - [[intercomparisons:d1_rayleigh|Rayleigh scattering]]
  - [[intercomparisons:d2_lambert|Lambertian surface]]
  - [[intercomparisons:d3_aerosol_spherical|Spherical aerosols]]
  - [[intercomparisons:d4_aerosol_spheroid|Spheroidal aerosols]]
  - [[intercomparisons:d5_water_cloud|Liquid water cloud]]
  - [[intercomparisons:d6_ocean|Ocean surface]]
  

=== E - Test cases for fully spherical geometry for a vertically inhomogeneous atmosphere ===
  - [[intercomparisons:e1_rayleigh|Rayleigh scattering, US standard atmosphere]]
  - [[intercomparisons:e2_absorption|Rayleigh scattering and molecular absorption, US standard atmosphere]]
  - [[intercomparisons:e3_aerosol|Tropospheric aerosol layer (desert dust)]]
  - [[intercomparisons:e4_aerosol_stratos|Tropospheric aerosol layer (desert dust) and stratospheric aerosol layer]]
  - [[intercomparisons:e5_cirrus|Cirrus cloud layer]]
  - [[intercomparisons:e6_ocean_planet|Ocean planet]]
International Polarized Radiative Transfer

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