Refractivity

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Refractivity

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1. The algebraic difference between an index of refraction and unity. </dd>
For the atmosphere, refractivity may be more conveniently expressed in N-units: N = (n - 1) 10E6 The deviation of the refractivity at any altitude from the usual standard profile is expressed in B-units (for radiofrequencies up to 20 kilomegacycles):
B = N + 0.12h where h is altitude in feet.
The deviation of the refractivity at any altitude from the gradient at which the refraction curvature of a tangential ray will match the curvature of the earth may be expressed in M- units:
M = N + 0.048h where 0.048 is 10E6 divided by the radius of the earth in feet. </p> </dd>
2. = index of refraction. </dd>
This usage should be discouraged. </dd>

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use