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user_area:rainbows_with_libradtran [2008/10/22 11:36]
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user_area:rainbows_with_libradtran [2008/10/22 12:31] (current)
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 ====== Rainbows with libRadtran ====== ====== Rainbows with libRadtran ======
  
-To calculate a rainbow with libRadtran is relatively straightforward. It is computationally expensive but to generate the input is quite simple. Rainbows form when we have large water droplets. For this reason we first need to calculate optical properties for a size distribution with large droplets. ​Ise the mie tool to do that. The input file is very short:+To calculate a rainbow with libRadtran is relatively straightforward. It is computationally expensive but to generate the input is quite simple. Rainbows form when we have large water droplets. For this reason we first need to calculate optical properties for a size distribution with large droplets. ​We may use the mie tool to do that. The input file is very short:
  
   mie_program MIEV0   mie_program MIEV0
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   size_distribution_file ./​sizedist_1.010   size_distribution_file ./​sizedist_1.010
  
-In order to get a realistic result, ​you need to define a size distribution on a reasonable grid (if a monodisperse distribution is assumed - that is, all droplets are same size - the result would show may spikes and individual features which cannot be observed in nature because a real cloud always includes a distribution of different droplet sizes). For our example we used a gamma distribution where the radius grid is incremented by a factor of 1.01 from wavelength to wavelength:+In order to get a realistic result, ​we need to define a size distribution on a reasonable grid (if a monodisperse distribution is assumed - that is, all droplets are same size - the result would show may spikes and individual features which cannot be observed in nature because a real cloud always includes a distribution of different droplet sizes). For our example we used a gamma distribution where the radius grid is incremented by a factor of 1.01 from wavelength to wavelength:
  
 {{:​user_area:​sizedist.png|}} {{:​user_area:​sizedist.png|}}
  
-The mie tools will then provide ​a number of optical property files in netcdf format for wavelengths between 380 and 780nm with a step of 5nm. These can be directly used as input to uvspec: ​+The mie tool provides ​a number of optical property files in netcdf format for wavelengths between 380 and 780nm with a step of 5nm. These can be directly used as input to uvspec: ​
  
   atmosphere_file ../​data/​atmmod/​afglus.dat   atmosphere_file ../​data/​atmmod/​afglus.dat
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   phi 0    phi 0 
  
-And the output will be colors which can be directly converted to a picture. Voila!+And the output will be colors which can be directly converted to a picture. In this example we have the sun at the zenith and look straight downward - hence we only need the viewing zenith angle dependence and don't need to care about the azimuth. Voila!
  
 {{:​user_area:​rainbow.png|}} {{:​user_area:​rainbow.png|}}
 
 
user_area/rainbows_with_libradtran.txt ยท Last modified: 2008/10/22 12:31 by admin
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