IEEE Spectrum February, 2011 - 20
hands on
Balloon-Borne PhotograPhy
get a bird's-eye view on a budget
A
lthough there's
a certain awe-inspiring
beauty to the images
that hobbyists' weather
balloons can capture from
the edge of space, in fact most
of the good stuff happens
much nearer the ground.
These flights can be
broken into three phases.
The first, with cool imagery of
the ground below, lasts about
10 seconds. In the second,
the balloon starts to swing
around wildly in the wind,
and you get a long period
of nausea-inducing footage.
Finally, the balloon ruptures,
transmitting a quicker but
equally queasy view as it
plummets earthward.
Since most of the
interesting images come in
the first 100 meters, why
go higher? Besides, by
keeping the balloon low,
you can control the pan
and zoom, rather than
trusting to dumb luck.
Setting up a balloon for
low-altitude observation
involves some interesting
logistical issues, but it isn't
particularly difficult. To begin
with, balloon flight is all about
payload weight. The more
you want to carry, the more
lift you'll need, meaning a
bigger balloon and more
helium. In the United States,
there's a practical limit to
both: FAA Part 101 regulates
what size and type of balloon
can be operated without
notifying the FAA prior to
flight. Moored balloons can't
have an inflated diameter of
more than 6 feet (1.8 meters)
20
or a capacity of more than
115 cubic feet (3256 liters).
These requirements will
pretty much drive all the
other decisions you make.
The best source I've
been able to find is Balloons
Direct. It sells a US $35
chloroprene weather balloon
with a 1.7-meter diameter
and a total fill capacity
of 2464 L-enough to lift
2.1 kilograms. I ordered
two, just to be safe.
Next I needed a payload.
There are lots of pan-zoomtilt webcams around, but
most require an Ethernet
connection, which would
leave little lift for the
camera-an altitude of
30 meters would require
an entire kilogram's worth
of Cat 5 cable. I turned my
attention to Wi-Fi-enabled
webcams, settling on the
Vivtek PZ7131. It features
640-by-480 resolution, a
2x optical zoom, and a winceinspiring $340 price tag.
The camera required
about 1.5 amperes at 12 volts.
I could have used lithiumion batteries, but because
I had to tether it anyway,
I decided to run 12 V up
on a wire from the ground,
using the power line as the
mooring line as well. I spent
an evening with my 15-yearold son braiding a 30-meter
length of two-conductor
wire out of some 22-gauge
single-conductor wire and
splicing it between a jack
and a spare 12-V power
cube. The lift penalty was
well under half a kilo. A test
NA * iEEE SpEctrum * fEbruAry 2011
confirmed that the camera
received enough power
to operate, so I was set.
I pulled a spare IEEE
802.11g wireless access point
out of my closet and attached
it to my MacBook via
Ethernet. The camera found
the access point, and the
MacBook found the camera's
Web browser interface, so
now I had a balloon, camera,
power, and networking.
All that was left was the
helium and the weather.
Helium isn't cheap
these days. The only place
it's being made locally is
the interior of the sun, so
we have what we have,
and it's running out fast.
Some analysts estimate
that the cost of helium is
about one-tenth of what
it really should be, given
the increasing scarcity.
In any event, your best
bet is a welding supply
house or industrial gas
supplier. You'll want a
125-cubic-foot (3540 L) tank,
which is about 1.2 meters tall
and is definitely awkward
for one person to move
around. You'll probably
need to put down a deposit
on the tank, and be sure to
ask for a balloon inflator.
That's one of those things
you see at party stores, but it
works for weather balloons,
too. My tank, courtesy of
Granite Industrial Gases,
in Derry, N.H., set me back
$60, and the company lent
me the inflator for free.
spectrum.ieee.org
http://spectrum.ieee.org
Table of Contents for the Digital Edition of IEEE Spectrum February, 2011
IEEE Spectrum February, 2011 - Cover1
IEEE Spectrum February, 2011 - Cover2
IEEE Spectrum February, 2011 - 1
IEEE Spectrum February, 2011 - 2
IEEE Spectrum February, 2011 - 3
IEEE Spectrum February, 2011 - 4
IEEE Spectrum February, 2011 - 5
IEEE Spectrum February, 2011 - 6
IEEE Spectrum February, 2011 - 7
IEEE Spectrum February, 2011 - 8
IEEE Spectrum February, 2011 - 9
IEEE Spectrum February, 2011 - 10
IEEE Spectrum February, 2011 - 11
IEEE Spectrum February, 2011 - 12
IEEE Spectrum February, 2011 - 13
IEEE Spectrum February, 2011 - 14
IEEE Spectrum February, 2011 - 15
IEEE Spectrum February, 2011 - 16
IEEE Spectrum February, 2011 - 17
IEEE Spectrum February, 2011 - 18
IEEE Spectrum February, 2011 - 19
IEEE Spectrum February, 2011 - 20
IEEE Spectrum February, 2011 - 21
IEEE Spectrum February, 2011 - 22
IEEE Spectrum February, 2011 - 23
IEEE Spectrum February, 2011 - 24
IEEE Spectrum February, 2011 - 25
IEEE Spectrum February, 2011 - 26
IEEE Spectrum February, 2011 - 27
IEEE Spectrum February, 2011 - 28
IEEE Spectrum February, 2011 - 29
IEEE Spectrum February, 2011 - 30
IEEE Spectrum February, 2011 - 31
IEEE Spectrum February, 2011 - 32
IEEE Spectrum February, 2011 - 33
IEEE Spectrum February, 2011 - 34
IEEE Spectrum February, 2011 - 35
IEEE Spectrum February, 2011 - 36
IEEE Spectrum February, 2011 - 37
IEEE Spectrum February, 2011 - 38
IEEE Spectrum February, 2011 - 39
IEEE Spectrum February, 2011 - 40
IEEE Spectrum February, 2011 - 41
IEEE Spectrum February, 2011 - 42
IEEE Spectrum February, 2011 - 43
IEEE Spectrum February, 2011 - 44
IEEE Spectrum February, 2011 - 45
IEEE Spectrum February, 2011 - 46
IEEE Spectrum February, 2011 - 47
IEEE Spectrum February, 2011 - 48
IEEE Spectrum February, 2011 - 49
IEEE Spectrum February, 2011 - 50
IEEE Spectrum February, 2011 - 51
IEEE Spectrum February, 2011 - 52
IEEE Spectrum February, 2011 - 53
IEEE Spectrum February, 2011 - 54
IEEE Spectrum February, 2011 - 55
IEEE Spectrum February, 2011 - 56
IEEE Spectrum February, 2011 - 57
IEEE Spectrum February, 2011 - 58
IEEE Spectrum February, 2011 - 59
IEEE Spectrum February, 2011 - 60
IEEE Spectrum February, 2011 - 61
IEEE Spectrum February, 2011 - 62
IEEE Spectrum February, 2011 - 63
IEEE Spectrum February, 2011 - 64
IEEE Spectrum February, 2011 - Cover3
IEEE Spectrum February, 2011 - Cover4
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