Satellites orbit Earth at altitudes above 250
miles; that is, if they want to
remain in orbit for any length
of time (although I’ve read
that spy satellites will lower
their orbits for higher
resolution images). Many
airplanes fly upwards of
30,000 feet and as low as
500 feet above the ground in
uncongested locations (there
are exceptions for airplanes
like crop dusters). However,
for images taken at altitude
below 400 feet and above
60,000 feet, there are no
practical and inexpensive
platforms except for the
quadcopter (drone) and the
BalloonSat.
Before discussing my experiences
with using quadcopters and
BalloonSats to image, I’d like to
describe my experiments using
instruments to record images in a
variety of spectral ranges. I’m testing
imaging techniques on the ground
and then moving them up to my
quadcopter for further testing. The
experience gained will then be used
to create a BalloonSat to collect
similar images from near space.
The types of imagers I’ve tested
so far include a color camera
(visible), a near infrared camera, and
thermal imager (long-wave infrared).
The imager I haven’t successfully
created is the near ultraviolet camera
(but I’ll keep working on it).
The Electromagnetic
Spectrum
During Isaac Newton’s lifetime,
physicists debated whether light was
best described as a particle or a
wave. Newton claimed that the
results of his experiment with prisms
were proof that light consisted of
particles or corpuscles as he
described them. Less than a
decade later, Christiaan
Huygens developed a theory
of light that proved light
could indeed be a wave and
still behave as physicists had
observed.
Astronomer William
Herschel later extended the
range of colors by discovering
a new region of the spectrum
that the human eye could not
see; a color he named
infrared (below red). One
year later, Johann Ritter did
something similar to Herschel
and discovered the existence
of light above violet. He
called this color Chemical
light, but it was renamed ultraviolet
since it was above violet.
Later in the 19th century, physicist
James Clerk Maxell noticed that he
could combine two equations that
described magnetic fields and two
equations that described electric
fields into the wave equation. The
equation indicated that the combined
electric and magnetic wave was self-supporting and traveled at the speed
of light. This was strong evidence that
light is indeed an electromagnetic
wave and that other “colors” of light
that we can’t see existed. Today,
Testing imaging methods in preparation for a future near space mission
makes me realize just how useful quadcopters and BalloonSats can be in
imaging Earth’s surface. Satellites and airplanes are the primary platforms in
use today. However, satellites are very high above the ground and
expensive, while airplanes are just mildly expensive and unable to safely
view the ground up close. This means drones like quadcopters are the
solution to Earth imaging very close to the ground and BalloonSats are the
cheap alternative to satellite-based imaging.
■ BY L. PAUL VERHAGE NEAR SPACE
Cheap Multispectral Imaging for
Amateur Science
16 December 2016
paul@nearsys.com
I built the carrier for this thermal imaging system
using Coroplast and Styrofoam. The quadcopter
then carried it up to an altitude of 400 feet AGL
for an aerial imaging experiment. Next stop,
near space!
