Zoom90 | 52Technical Data
Air humidity The air humidity influences the distance measurement if the climate is extremely hot and damp.
For high precision measurements, the relative humidity must be measured and entered along with the air
pressure and the temperature.
Air humidity correction
Index n
The index n is calculated from the formula of the IAG Resolutions (1999), and is valid for:
Formulas
D
1
Atmospheric correction [ppm]
p Air pressure [mbar]
t Air temperature [°C]
h Relative humidity [%]
x (7.5 * t/(237.3 + t)) + 0.7857
If the basic value of 60 % relative humidity as used by the EDM is retained, the maximum possible error
in the calculated atmospheric correction is 2 ppm, 2 mm/km.
Reduction to mean sea
level D
2
The values for D
2
are always negative and are derived from the following formula:
ppm Air humidity correction [mm/km]
% Relative humidity [%]
C° Air temperature [°C]
ppm
+5
+1
+2
+3
+4
+0
-10-20 0 10 20 30 40 50 °C
100%
80%
60%
40%
20%
TS_104
Type Index n carrier wave [nm]
combined EDM 1.0002863 658
Air pressure p: 1013.25 mbar
Air temperature t: 12 °C
Relative air humidity h: 60 %
Formula for visible red laser
· 10
x
4.126 · 10
-4
· h
-
0.29535 · p
ΔD
1
= 286.338 -
002419_002
1
273.15
D
2
Reduction to mean sea level [ppm]
H Height of EDM above sea level [m]
R 6.378 * 10
6
m
TS_106
ΔD
2
= -
H
R
· 10
6
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