Effective earth radius
Re = effearthradius
Re = effearthradius(RGradient)
Re = effearthradius returns the effective radius of spherical earth in meters. The calculation uses a refractivity gradient of -39e-9. As a result, Re is approximately 4/3 of the actual earth radius.
Refractivity gradient in units of 1/meter. This value must be a nonpositive scalar.
The effective earth radius is a scaling of the actual earth radius. The scale factor is:
where r is the actual earth radius in meters and RGradient is the refractivity gradient. The refractivity gradient, which depends on the altitude, is the rate of change of refraction index with altitude. The refraction index for a given altitude is the ratio between the free-space propagation speed and the propagation speed in the air band at that altitude.
The most commonly used scale factor is 4/3. This value corresponds to a refractivity gradient of .