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4
Appendix I Use of CTD-Divers at Varying Elevations
CTD-Divers can be used at any elevation ranging from 300 meters below sea level to 5,000 meters
above sea level. It is however recommended that all Divers and the Baro-Diver forming part of the
same network be used at the same elevation (whenever possible).
The relationship between atmospheric pressure variations and elevation is exponential, rather than
linear:
P
H
= P
0
· exp[ (M·g·H)/(R·T)]
where
P
H
= atmospheric pressure at elevation height H
P
0
= atmospheric pressure at reference height
M = 28.8 · 10
-3
kg/mol (molecular mass of air)
g = 9.81 m/s
2
(standard gravity)
H = height in meters
R = 8.314 J/mol/K (gas constant)
T = temperature in Kelvin
If the Baro-Diver is placed at a different elevation from the other Divers in a monitoring network, it is
possible for a deviation to occur in the barometrically compensated data due to the relationships
referred to above. The graph below illustrates the deviation in the barometric data as a function of the
variation in elevation at 5
C and 25
C.
To determine the relative barometric pressure deviation relative to P
0
at 5
C (T = 278.15
K) at a height
differential of H, the above referenced formula can be used:
(P
H
- P
0
) / P
0
= 1 exp[ (M·g·H)/(R·T)] × 100%
(6)
By substituting the data, a relative deviation of 1.2 % at a height differential of 100 m is obtained. At a
height differential of 1,000 m this increases to 11.5 %.
We therefore recommend that all Divers and the Baro-Divers in a network be placed such that the
mutual height differentials are minimized.
If necessary, multiple Baro-Divers can be deployed to avoid the abovementioned issues.
0%
5%
10%
15%
20%
25%
30%
0
1000
2000
3000
d
e
v
ia
ti
o
n
[%
]
altitude [m]
5 °C
25 °C
Содержание CTD-Diver DI28 Series
Страница 1: ...CTD Diver DI28x Series...
