An improved calibration for tethered balloon wind measurements |
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| Authors: | W W Moriarty |
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| Institution: | (1) Moriarty Meteorological Services, 143 Reservoir Rd., Sunbury, Victoria, Australia |
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| Abstract: | A previously published technique for using tethered spherical balloons as anemometers for measuring light low-level winds has been further developed. Earlier data on the relationship between the aerodynamic drag coefficient and the Reynolds number of spherical rubber balloons were combined with a large number of new data and re-analysed; and the errors in the relationship were estimated. The results allowed a more accurate calculation of wind speed from the deflection of a tethered balloon from the vertical. When combined with a new technique for calculating the effects of the tether, this enabled light to moderate low-level winds at fixed heights up to 600 m or more to be measured with simple, cheap, and readily mobile equipment; and a slight modification of the technique allowed measurement of winds in and above fog. Wind speeds measured by the ballon technique showed reasonably good agreement with measurements by an anemometer carried beneath the balloon.Glossary of Symbols
a, b, c
Coefficients in the relationship between lnC
d
and lnR
-
A
Quantity under square root in solution for lnV whena 0
-
C
d
Wind drag coefficient for balloon
-
C
dc
Value ofC
d
given by calibration curve of Table I
- D
Dynamic wind pressure force on balloon
- F
Buoyant free lift of balloon with load
- Re
Reynold's number of balloon (sphere)
-
R
= Re/105
-
r
Radius of sphere
- T
Tension in tether
-
V
Wind speed
-  83(  )
=(lnC
dc
-lnC
d
) when  83° , or 0 for other
- 
Error in lnC
d
-
Elevation of tether where attached to balloon
- 
Elevation of balloon from ground tether point
-
Molecular viscosity of air
- 
Ratio of circumference to diameter of circle
- 
Density of air |
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| Keywords: | |
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