In levelling, the combined correction for earth curvature and atmospheric refraction for a distance D (in km) is given by:
A- 0.0785 D^2 meters
B+ 0.0112 D^2 meters
C- 0.0673 D^2 meters
D- 0.1352 D^2 meters
Explanation
Curvature correction Cc = -0.0785 D^2 (downward/subtractive). Refraction correction Cr = +0.0112 D^2 (upward/additive). Combined correction C = Cc + Cr = -0.0673 D^2 meters.

No Comments