Difference between revisions of "Refractivity"

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(Created page with "The refractive index (n) of air is defined as: \dfrac{c}{v} = n")
 
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The refractive index (n) of air is defined as:
 
The refractive index (n) of air is defined as:
  
\dfrac{c}{v} = n
+
n = c/v
 +
 
 +
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

Revision as of 15:00, 21 February 2020

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

n = c/v

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