Difference between revisions of "Refractivity"

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n = c/v
 
n = c/v
 +
 +
[[File:equationtest.wmf]]
  
 
where:
 
where:

Latest revision as of 15:32, 21 February 2020

The refractive index (n) of air is defined as:

n = c/v

File:Equationtest.wmf

where:

  • c is the velocity of light in a vacuum.
  • v is the velocity of light in air.

A typical value of n is 1.000301. For convenience the refractive index is expressed as refractivity (N)

N = (n-1) x 10^6

which results in a typical value of 301 Refractivity is defined by the equation:

N = 77.6 x (P/T) + 3.732 x 10^5 x (e/T^2)

where:

  • P is the atmospheric pressure.
  • T is the absolute temperature.
  • e is the water vapor pressure.
  • N varies with elevation. In a well mixed troposphere, the variation is exponential; however, in the range from 1 to 2 kilometers above sea level, the variation is approximately linear. This is referred to as a constant refractivity gradient. The refractivity gradient determines the microwave beam-bending.

Handling the variations of refractivity with elevation is the major challenge in the design of high reliability microwave links