The index n is calculated from the formula of the IAG Resolutions (1999), and
is valid for:
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
Δ
D
1
= 286.338 -
002419_002
D
D
1
Atmospheric correction [ppm]
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
D
D
2
are always negative and are derived from the following for-
mula:
TS_106
Δ
D
2
= -
H
R
· 10
6
D
D
2
Reduction to mean sea level [ppm]
H
Height of EDM above sea level [m]
R
6.378 * 10
6
m
The magnitude of the projection distortion is in accordance with the projection
system used in a particular country, for which official tables are generally avail-
able. The following formula is valid for cylindrical projections such as that of
Gauss-Krüger:
TS_107
Δ
D
3
=
X
2
2R
2
· 10
6
D
D
3
Projection distortion [ppm]
X
Easting, distance from projection
zero line with the scale factor 1
[km]
R
6.378 * 10
6
m
In countries where the scale factor is not unity, this formula cannot be directly
applied.
Formulas
Reduction to mean
sea level
D
D
2
Projection distortion
D
D
3
Technical Data
65
