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) Ecorr = E + (78.5/k) x 10-3 x D x (P-D)
Ecorr 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) Ecorr = E + (D x {P-D}) / (1.5 x k)
Ecorr is the corrected elevation in feet.
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
D1 and D2:
(2) Ecorr = E + (D1 x D2) / (1.5 x k)
Ecorr is the corrected elevation in feet.
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.
D1 is the horizontal distance along the path from the primary site to the point being corrected (in miles).
D2 is the horizontal distance along the path from the point being corrected to the end of the path (in miles).
Copyright 1999 by SoftWright LLC
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