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Air humidity
correction
Index n
Formulas
Reduction to mean
sea level DD
2
Projection distortion
DD
3
66
ppm
+5
+4
+3
+2
+1
+0
-20
-10
0
10 20 30 40 50
TS_104
Type
Combined EDM
The index n is calculated from the formula of the IAG Resolutions (1999), and
is valid for:
Air pressure p:
Air temperature t:
Relative air humidity h:
Formula for visible red laser
0.29535 · p
ΔD
= 286.338 -
1
002419_002
Atmospheric correction [ppm]
DD
1
p
Air pressure [mbar]
t
Air temperature [°C]
h
Relative humidity [%]
a
1
273.15
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.
The values for DD
are always negative and are derived from the following for-
2
mula:
H
ΔD
6
= -
· 10
2
R
TS_106
The magnitude of the projection distortion is in accordance with the projection
system used in a particular country, for which official tables are generally
100%
80%
60%
40%
ppm
20%
%
°C
°C
Index n
1.0002863
1013.25 mbar
12 °C
60%
-4
4.126 · 10
· h
x
-
· 10
Reduction to mean sea level [ppm]
DD
2
H
Height of EDM above sea level [m]
R
6.378 * 10
Air humidity correction
[mm/km]
Relative humidity [%]
Air temperature [°C]
Carrier wave [nm]
658
6
m
Technical Data
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