when theater gels block all of
the visible light, only infrared is
allowed to pass through.
Recently, the long-wave
infrared portion of the spectrum
has opened to amateur use.
Thermal imagers — like the
Reveal by Seek — creates and
records thermal images in the 8
to 15 micrometer ( 8,000-15,000
nm) range by using a
chalcogenide lens and a micro-bolometer in place of a glass
oxide lens and CMOS imager.
For curious readers, the
chalcogens are elements in the
oxygen family of elements (group 6A
elements in the periodic table of the
elements). In a chalcogenide lens,
oxygen (oxide) is switched with
sulfur, selenium, or tellurium. The
replacement of the oxide lens of a
tradition camera with a chalcogenide
one makes the lens transparent to
long-wave infrared, which normal
glass is not.
The second step in creating a
thermal imager is to replace the
CMOS imager with a bolometer. A
bolometer consists of an array of
small cells like a CMOS imager.
However, the cells in a bolometer
measure the temperature of the cell
instead of the intensity of the light
shining on them.
In the case of the Seek Reveal,
the micro-bolometer is an array of
206 by 156 cells or pixels, so
nowhere near the resolution of a
modern CMOS imager. Images in the
Reveal are coded yellow and white
for warm pixels and a blue to black
for colder pixels. The resulting image
is a temperature map of the object(s)
observed.
So far, my experiment
The problem is that a black light
creates ultraviolet radiation by
operating at high temperatures. The
bulb’s high temperature means the
glass must also be transparent in the
infrared or else it damages or breaks
the glass. The result is that the
ultraviolet filter I used transmits
both NIR and UV. Therefore, at
this time, I’m still looking for a
filter that blocks NIR and is
visible while transmitting UV.
There are three cameras
and three regions of the
electromagnetic spectrum
covered so far. I’m interested to
hear if any readers are
experimenting with amateur
multispectral imaging and what
tools they’re using. In my next
article, I’ll show some of the results
achieved by my quadcopter so far.
It’s not using a gimbal to support the
imaging systems, so the pictures can
be blurry at times.
18 December 2016
Drone Laws
Drones like quadcopters are a lot of fun to fly. I’m discovering some of the
new ways people and organizations are using them to do real science.
Unfortunately, some people are expressing a fear for their misuse. I have to
admit that quadcopters do make it easier to spy on neighbors or to collect
undesired data about farm and ranch operations. In response to these real and
perceived threats, some states are passing laws restricting drone use. Earlier
this year, I had the opportunity to learn about Idaho’s drone law.
While performing the imaging experiments with the tools I’m describing in
this article, my quadcopter flashed all four of its status LEDs white — an
indication of a GPS error. My quadcopter has a software geofence limiting its
flight range to 600 feet. Unfortunately, firmware onboard the quadcopter didn’t
respond well to the GPS error; it flew away and was non-responsive to my
commands.
My quadcopter is registered with the FAA and
has my phone number written prominently on it.
(That’s because I’m a responsible drone pilot and
want my expensive quadcopter back should it crash.)
Because of its marking, I was confident I’d get a
phone call about it during harvest time when a
farmer came across it. To my surprise, I actually got
the phone call from the Canyon County Sheriff’s
Office only an hour after the fly-away.
It turns out my quadcopter flew 4,000 feet away
(or six times beyond its geofence), and landed in a
yard of a concerned citizen who just happened to be
my local legislator. It took about seven weeks to get
this resolved, and I want to thank the Sheriff’s office
for handling this. They did a very professional job.
Now, all parties understand the landing was
unintentional, the result of a failure, and not an
attempt to spy.
One concern I’ve heard voiced because of this
incident is that some people believe that thermal
imagers can see through walls and into homes. To
show this is not the case, I want to show the image here that I took while
looking at a window of my house. The curtain was pulled back and I could see
inside my house. However, you’ll notice that the thermal imager only sees my
reflection.
Window glass is not transparent to heat and therefore not transparent to
long-wave infrared. However, it is reflective. The only thing a commercial
thermal imager can show is the warmth of a surface and not the heat of objects
on the other side of a wall or window.
Please check your state laws before flying your drone. I know Idaho and
Texas have drone laws that can affect how and where you can fly.
Nope. Can’t see
inside this house with
a thermal imager.
The tree, now viewed
in long-wave infrared.
This image indicates
that the tree’s leaves
are warmer than the
lawn below the tree.
Also, the lawn and
road behind the tree
are warmer than the
tree. A few scattered
cool clouds are visible
in the cold (therefore,
black in color) sky.
