Radiosonde Flight Notes
The radiotheodolite manual has detailed instructions.
When repacking, leave the antenna arms attached to the pedestal.
Orient the pedestal and initialize the azimuth and elevation as described
in the manual.
The decoder box is newer than the radiotheodolite, so the intercabling
is undocumented. The radiotheodolite I/O jack (J2) and the decoder box
data I/O jack are connected with a multiconductor cable (SA-106336). There's
also an extension cable for this connection. The decoder box RT data and
PTU data jacks are connected to the com ports on the Austin laptop computer.
It doesn't matter which com port is connected to which data jack.
The main radiotheodolite cable (black Y-cable) connecting the pedestal
to the panel is only long enough for one 360 degree azimuth wrap. Take
the upper atmosphere wind direction into account when setting up the radiotheodolite!
Connect an external monitor to the computer. This is optional, but makes
it much easier to see the displays.
The equipment has been verified with 110 VAC, 60 Hz electrical power. Take
care before using any other source.
Install regulator on helium tank and open tank valve.
Open inflation (tilt) valve and purge supply hose.
The valve is weighted to balance a net lift of 300 g, which should give
an ascent rate of about 5 m s-1 (1000 ft min-1; see
Insert the inflation valve into the balloon neck and fill the balloon to
neutral buoyancy when weighted by the valve assembly and about 60 cm of
hose. Caution: when the balloon is flaccid, the canopy can be punctured
by the gas flow from the inflation valve.
Tie off balloon neck with string.
Close tank valve.
Startup, calibration, and flight
Boot the computer and choose option 8 (old version of MS-DOS) from
the start up menu. The radiosonde software will start automatically. Turn
on radiotheodolite and decoder box.
From the main menu, select run flight program. The program automatically
selects and sets up the communications ports.
In the station and flight data initialization screen, enter station
2, altitude 5000 m. Leave other parameters to defaults. Press F10
to continue to the next screen.
When the sensor verification screen is displayed, unpack a sonde,
deploy the antenna and sensors, and turn it on by installing the jumper
on the bottom. Place it outside near the radiotheodolite. If necessary,
adjust the radiotheodolite frequency with the hand paddle to lock onto
the signal (see manual). The sonde frequency can be adjusted with a small
screwdriver through a hole on the bottom. Turn the sonde off and on again
as necessary to record the calibration data. The sonde uses three standard
9 V alkaline batteries, should it ever be necessary to replace them.
After those data are recorded, press F10 to continue to the next
screen. Don't enter surface values. Make sure the radiotheodolite has autotrack
and AFC enabled on the hand paddle. Attach the sonde to the balloon with
2 m of string.
From the prelaunch sensor data screen, the program will automatically
detect the launch or you can initiate data acquisition by pressing F10.
Make sure the radiotheodolite is tracking the sonde and release the balloon
about 30 m away from the radiotheodolite..
Some time after launch, the program will display data in the text screen.
Pull down the graphics menu for more useful displays. Ignore the repeated
requests for surface data.
The radiotheodolite should track the balloon to burst at about 20 km altitude.
In good weather, the balloon can be seen in the boresight telescope until
burst. The program may automatically detect balloon burst. Then it may
be possible (and interesting) to track the descent. The humidity sensor
has, however, a substantial time constant. Use the quit menu to
terminate data acquisition and then quit from the main menu to DOS.
Reboot the computer to Win95 (option 1, default) to examine data,
Balloon ascent rate
The balance between the balloon's buoyant lift and its aerodynamic drag
and the balloon and package weight determines the ascent rate,
L = D + W ,
(4p/3) r3 (rair
- rHe) g = Cd
+ (Msonde + Mballoon)
Here r is the balloon radius, the sea level densities of air and
helium, rair = 1.225 kg m-3
and rHe = 0.169 kg m-3,
the gravitational acceleration g = 9.8 m s-2, v
is the ascent rate, the sonde mass Msonde = 250 g, and
the balloon mass Mballoon = 100 g. For a flow of 5 m
s-1 and a characteristic length of 1 m, the Reynolds number
= vl/n »
3 × 105, where the kinematic viscosity of air n
= 1.46 × 105 m2 s-1. This is just
the critical Reynolds number for the onset of a turbulent boundary layer
when the drag coefficient Cd drops abruptly from »
0.4 to » 0.1. Hence the ascent rate cannot
be calculated precisely, but Cd = 0.2 is adequate for
estimation. Inasmuch as air and helium are perfect gases, the buoyant lift
of a sealed balloon is independent of altitude. The drag is a weakly decreasing
function of altitude, so the ascent rate slowly increases with altitude.
At sea level, a net lift of 300 g inflates a balloon to about 1 m diameter
and the approximate initial ascent rate is 5.2 m s-1 (1030 ft
min-1). At 5000 m altitude, the same lift will inflate the balloon
to 1.26 m diameter and the ascent rate will be about 5.7 m s-1.
Reference: Daily, J. W., & Harleman, D. R. F., 1966, Fluid
|tilt valve with pipe fitting
|small hose clamp
|larger hose clamp
|3/8" clear vinyl tube
0.75 g cm-1
|3/8" reinforced vinyl tube
1.65 g cm-1
|3/4"-10 steel nut
|3/4" flat washer
If ever necessary, reinstall the software from the AIR diskette following
the directions in the manual. Reboot and choose option 8 (old version
of MS-DOS) from the start up menu before doing this. Choose the color
EGA/VGA CRT video drivers, not the monochrome LCD.
Last modified 1998 September 28