==== Case E3: US standard atmosphere and tropospheric aerosol layer ====

In this case we include the US standard atmosphere, the corresponding Rayleigh scattering optical thickness and molecular absorption profiles are provided at 450 nm.
In addition an aerosol layer is added between 0 and 3km altitude. 

//Setup://

  * model atmosphere US-standard, scattering optical thickness provided in file {{:intercomparisons:phase_e:tau_rayleigh_450nm_usstd.dat|}}, molecular absorption optical thicknes in {{:intercomparisons:phase_e:tau_absorption_450nm_usstd.dat|}}. The file includes 2 columns where the first is the altitude of the layer boundaries in km, and the second is the layer optical thickness (e.g. the value for 0 km corresponds to the optical thickness for the layer from 0 to 1 km).
  * desert dust aerosol between 0 and 3 km altitude with an optical thickness of 0.5. The aerosol optical properties are given in the file {{:intercomparisons:phase_e:desert.cdf}}. The format of the file is the same as in case D4.                                                      * wavelength: 450 nm 
  * Rayleigh depolarization factor: 0.03
  * surface albedo: 0
  * Earth radius: 6371 km
 

  * Sun-observer geometries as defined in general settings:
      * //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 altitude// (km): 0, 120