Modified Index of Refraction
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Modified Index of Refraction
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An atmospheric index
of refraction mathematically modified so that when its gradient is applied
to energy propagation over a hypothetical flat earth it is substantially
equivalent to propagation over the true curved earth with the actual index of
refraction. Also called refractive modulus, modified refractive index.
Compare potential
index of refraction.
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The modified index of refraction is usually expressed in M-units;
mathematically
is the index of refraction at a point in the atmospheric; h is the height above mean sea level of that point; a is the radius of the earth; and N is the index of refraction in N-units. In ray tracing problems, the vertical gradient dM/dh can be used directly to obtain a ray path curvature that is relative to the curvature of the earth, i.e.,
is a value by which the earth's radius is multiplied to get the radius of curvature of the ray path; ka is called the effective earth radius. </dd>
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
