Attenuation by Atmospheric Gases

• Summation of individual resonance lines

• Atmospheric profile for required location

  • dry air pressure
  • water vapour pressure
  • temperature

• Reference Standard Atmospheres (Rec. P.835)

• Earth-space propagation path

  • integration through atmosphere
  • station altitude and elevation angle
  • refractive index (p, T, e)

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• Model sums individual resonance lines for oxygen and water vapour

• Need information on dry air pressure, temperature and water vapour density at location and season concerned. For slant path, need profiles of these; can use local data or reference atmospheres for different latitude zones and seasons.

• For an Earth-space path, attenuation is calculated by integrating upwards through atmosphere, taking account of station altitude and elevation angle to satellite. For this, have to take account of refractive effects (which influences effective path length) and these effects will in turn also be function of p, T and e.