Low-Cost Sounding Balloon Experiment
A revista americana The Physics
Teacher (com mais de 10 mil assinantes
em todo o mundo) publicou na edição de dezembro
um artigo intitulado A Low-Cost Sounding
Balloon Experiment, sobre o Balão de
Estudos Atmosféricos desenvolvido pelos alunos
Bruno Muta Vivas e Gustavo Guerra Fernandes,
do Terceiro Ano do Colégio Poliedro.
artigo foi escrito por Marcelo Saba, presidente
do Clube Quark, pelo engenheiro Luiz Gustavo
Mirisola, da Universidade de Coimbra (Portugal),
e por Márcio Iguchi, ex-aluno do Poliedro
e estudante de graduação do Instituto Tecnológico
de Aeronáutica (ITA).
texto, os autores trazem a descrição do funcionamento
do balão atmosférico que possui baixo-custo
sem, contudo, prejudicar sua capacidade e
precisão de análise de dados. Outro aspecto
importante avaliado no texto é que o balão
pode ser recuperado, ao contrário dos balões
meteorológicos usados hoje em dia, que emitem
dados por ondas de rádio, sobem a altitudes
elevadíssimas e se perdem no espaço.
Acompanhe o artigo:
Low-Cost Sounding Balloon Experiment
Marcelo M. F. Saba
Instituto Nacional de Pesquisas Espaciais
/ Clube de Ciências Quark — Brazil
Luiz G. B.
Institute of Systems and Robotics, University
of Coimbra — Portugal
Instituto Tecnológico de Aeronáutica - ITA
/ Colégio Poliedro — Brazil
meteorological balloons customarily launched
from our city, we wondered how we could develop
an experiment to allow our students to effectively
gather data about the low atmosphere and at
the same time keep our limited financial budget.
When you hear about atmospheric balloons,
you usually think about balloons with large
envelopes of nylon or mylar with payloads
between 1 or 10 kg. They ascend to very high
altitudes, have a data radio transmitter,
and are not recoverable. This setup would
be too expensive for us. In order to keep
the cost low, the payload containing the data
recorded had to be recovered, and therefore,
the balloon must not go tens of kilometers
away. We ruled out tethered balloons, which
would not have recovery problems but can hardly
go beyond 100 m high because of the weight
of the tether and of lateral winds. Based
on some estimates of ascension speed for small
balloons and probable horizontal wind intensities,
we decided that in order to easily recover
the payload we had to limit its ascension
to about 2 km high. At this altitude, the
payload would have to be released from the
balloon by means of a timer.
Setup and Payload Recovering
Our envelope (see Fig.
1) consists of four latex 1-m diameter balloons
(the biggest we could get) of the kind used
at children's parties. Altogether they had
a net buoyancy capacity of 500 g. By net buoyancy,
we mean the payload the balloon can handle
after lifting its own weight. Many balloons
obviously have a worse weight/volume ratio
than one big balloon, but latex balloons are
two orders of magnitude cheaper than mylar
Apart from that, using more than one balloon
allows us to forget about parachutes (which
may fail to open). The payload goes up with
four balloons, and after a predefined time
a rope is cut, releasing three balloons. The
payload then falls down with just one balloon,
which provides a drag force comparable with
a parachute of approximately 40 cm of diameter.
Using the balloon as a "parachute" has a twofold
advantage to help us follow its fall visually.
First, it is bigger than the parachute. Second,
it stays aloft after the payload has hit the
To cut the
rope that liberates the balloon-parachute
and its payload, we used an electronic RC delay timer circuit.
We used the timer circuit shown in Fig. 2.
Several other and more precise timing circuits
can be found on the Internet (e.g. http://www.interq.or.jp/japan/se-inoue/e_ckt4.htm
Five minutes after launching it activates
a relay that connects a 9-V battery to a Ni-Cr
wire (6 cm, 40 , taken from a 1.5-k wire resistor),
which is wound around a polypropylene rope.
The current from the battery heats the Ni-Cr
wire, easily burning and severing the rope
in a few seconds.
Recording and Analysis
We decided that an interesting
parameter to measure in the atmosphere would
be the temperature profile. Temperature decrease
with altitude is something that most students
have experienced when traveling to high-altitude
used to accomplish this was a thermistor, whose resistance-versus-temperature
curve was obtained in our lab. The thermistor,
an NTC 10 k, was used as a variable resistor
in a 555 astable multi-vibrator oscillator
circuit (Fig. 3), which generates a sound
that was recorded by a portable sound recorder.
The sound frequency is thus related to the
resistance of the thermistor. After recovery,
we used shareware spectrum analyzer software
to read the frequency value over time (Fig.
the balloon taking off, placing a camera some
hundreds of meters away in order to measure
its ascension speed. The calculated speed
was 4.6 m/s (it reaches constant speed almost
immediately); therefore, supposing that this
speed remains constant over all the flight,
our 5-min interval allowed it to reach a height
of around 1400 m. Data from meteorological
sounding balloons show that the assumption
of a constant ascension speed of around 5
m/s is very reasonable.
To calculate the falling speed, we need to
know how long the balloon took to fall. We
could see the payload releasing and the balloon
hitting the ground (it landed 1 km away),
but even if we had not recorded this time
or seen these events, we could easily have
recorded the time interval between the instant
the lowest temperature was recorded
on the tape and the time at which the impact
sound with the ground was heard. A typical
descent took about 2 min 40 s, which gives
a descending speed of 7.5 m/s. We could hear
ourselves screaming "launching" when the system
took off, which allowed us to check the ascension
Figure 5 shows the temperature readings during
the flight, highlighting taking off and landing.
The minimum temperature recorded, which corresponds
to the highest point, was 28°C.
Supposing constant speed, Fig. 6 shows
the temperature profiles both (a) during ascension
and (b) during the fall. The meteorological
literature tells us to expect a variation
from 5 to 6°C/km of altitude, which is close
to our results. Notice how the two plots show
the same artifacts at higher altitudes. At
low altitudes they differ by some degrees.
The reason may be that the system was launched
over a sandy terrain and landed over dense
Note also that just after landing, the temperature
jumps almost 2°C and then continues rising
to 38°C. The sensor fell over some trees where
it may have touched warmer material heated
by sunlight. Once inside this forest the temperature
increased even more, perhaps due to a sort
of greenhouse effect.
We launched a sounding balloon through
the first kilometers of the atmosphere, measuring
high-resolution temperature data with fair
accuracy, while keeping the budget comfortably
In order to minimize the risk of losing the
balloon and payload, we chose a large open
area (see Fig. 7), waited for a calm wind,
and set the timer for a run of a few minutes.
This enabled us to visually follow the whole
flight and recover the balloon soon after.
(to be tested in the next flight) would be
to use a walkie-talkie to transmit the sound
signal to the ground. Additionally, other
sensors (pressure, humidity) could be added
using other astable circuits, which can be
set to a different frequency range.
movies can be downloaded from the Quark website
The authors would like to thank the students
Gustavo Guerra Fernandes, Bruno Muta Vivas,
and Colégio Poliedro for their help with this
[e.g., Phys. Rev. D 40, 2172 (1989)] go to
online journal abstracts. Other links (see
Reference Information) are available with
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by R.S. Horne, available at http://www.visualizationsoftware.com/gram.html
Links to other commercial and freeware programs
for audio spectrum analysis are at http://www.visualizationsoftware.com/gram/links.html
first citation in article
About the Author
received his Ph.D. in space science from the
National Institute for Space Research in Brazil.
His research interest is in the area of lightning
physics and physics education. He coordinates
the Quark Science Club (http://www.clubequark.org.br/)
where high school and undergraduate students
have a lot of fun developing new hands-on
physics research projects.Instituto Nacional
de Pesquisas Espaciais / Clube de Ciências
Quark - Brazil; firstname.lastname@example.org
Luiz G. B.
Mirisola is currently a Ph.D. student at the
University of Coimbra, Portugal. He holds
M.Sc. degrees in engineering from the Carnegie
Mellon University, USA and from the State
University of Campinas, Brazil. His research
interests are in the robotics area, where
he has worked mainly with autonomous airships.
He enjoyed the opportunity of leading younger
students in hands-on research projects in
the Quark Science Club.Institute of Systems
and Robotics, University of Coimbra - Portugal
is an undergraduate student at the Instituto
Tecnológico de Aeronáutica. He has been advising
high school students in the Quark Science
Club, providing young people the opportunity
to embrace the wonder of physics and rewards
through scientific competitions.Instituto
Tecnológico de Aeronáutica - ITA/Colégio Poliedro
Revista The Physics Teacher, Vol.
43, No. 9, pp. 578–581, Dezembro/2005