- Troposphere (clear air) -Super-refraction and ducting

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• Second case when considering propagation in the clear neutral atmosphere.

• Diagram shows the behaviour of a ray in the atmosphere for:
  • standard atmosphere with ref. gradient –40 N-units/km, in which the ray is bent slightly towards Earth
  • with gradient less negative, where ray path is away from Earth (said to be sub-refractive conditions)
  • with gradient more negative, where ray is bent more strongly towards Earth until the gradient of –157 N-units/km is reached when ray travels parallel to Earth’s surface. At this point, the ray is ducted.
  • Between –40 and –157, the conditions are said to be super-refractive.