For Example:
The air temperature is +15 ℃
The atmospheric pressure is 1013 hPa
From the chart, the atmospheric correction is about -5 ppm
16.2. Refraction and Earth Curvature Correction
Considering the correction of refraction and earth curvature for distance
measurement, the formula for SD, HD and VD applied in the instrument are as followings:
HD = Y - A × X × Y
VD = X + B × Y
2
HD: corrected horizontal distance
VD: corrected vertical distance
Y = SD × │sin ξ │
X = SD × cos ξ
SD: corrected slope distance
ξ： the ZA （zenith 0）
A = (1 – k / 2) / R
B = (1 – k / 2) / 2R
k: atmospheric refractive index, default 0.13
R: average radius of the earth 6.37 × 10
6
m
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