**Q**: How is earth curvature correction calculated?

**A:** TAP software which uses radial elevation data (for
plotting radial profiles, computing radio propagation obstruction
losses, etc.) allows elevation values to be corrected for earth
curvature, including atmospheric diffraction effects.

The formula used for elevation correction is:

(1) E_{corr} = E + (78.5/k) x 10^{-3} x D x (P-D)

E_{corr} is the corrected elevation in **meters.**

E is the actual elevation in **meters**.

k is the curvature correction factor to compensate for atmospheric diffraction, typically 4/3 for most radio propagation applications. To ignore atmospheric diffraction, use a value of 1.0 for this factor.

D is the horizontal distance along the path from the primary
site to the point being corrected (in **kilometers**).

P is the distance from the site to the end of the path (in
**kilometers**).

The equation can also be written using British units as:

(2) E_{corr} = E + (D x {P-D}) / (1.5 x k)

E

_{corr}is the corrected elevation infeet.E is the actual elevation in

feet.k is the curvature correction factor to compensate for atmospheric diffraction, typically 4/3 for most radio propagation applications. To ignore atmospheric diffraction, use a value of 1.0 for this factor.

D is the horizontal distance along the path from the primary site to the point being corrected (in

miles).P is the distance from the site to the end of the path (in

miles).

Since the term {P-D} is the distance from the point being corrected
to the far end of the path, the equation can also be written in terms of
the distances

D_{1} and D_{2}:

(2) E_{corr} = E
+ (D_{1} x D_{2}) / (1.5 x k)

E

_{corr}is the corrected elevation infeet.E is the actual elevation in

feet.k is the curvature correction factor to compensate for atmospheric diffraction, typically 4/3 for most radio propagation applications. To ignore atmospheric diffraction, use a value of 1.0 for this factor.

D

_{1}is the horizontal distance along the path from the primary site to the point being corrected (inmiles).D

_{2}is the horizontal distance along the path from the point being corrected to the end of the path (inmiles).

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