Curvature correction in electronic distance measurement

The usual methods for curvature correction, which consist of a geometric and a velocity component, are based on standard atmospheric conditions and thus take no account of variable refraction. A formula has been developed expressing the correction as a function of atmospheric refraction: K=(1-k_² S²/(24 R²) whereS is the measured distance, R is the radius of the earth, and k is the coefficient of refraction. This formula leads to a practical procedure employing trigonometric levelling in the determination of curvature correction for long-range geodimeter measurements.