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By detecting very subtle temperature differences of everything in view, infrared technology reveals what otherwise would be invisible to the naked eye.

Thermal:

ther•mal; 'THərməl/adjective: thermal

  1. of or relating to heat.

Imaging: im•age; 'imij/verb: gerund or present participle

  1. make a representation of the external form of.

Pretty obvious. We make images of heat. Think about how an image is made with your smartphone camera. Visible light reflects off the objects you want to image, that light comes into a lens, it is focused on a sensor, and an image is delivered. The same thing can be done with heat coming from the object. You might wonder how do you focus on heat? What kind of sensor detects heat? How do you display heat? All good questions.

Just as in any science or technology, there are armies of brilliant people making thermal imaging products better all the time. Just like the evolution from early PCs with C:\> to how we function with smartphones, thermal imagers have come a long way. But very simply, thermal imaging is your thermal scene, a lens, a sensor, and a display. It's as simple as that.

INFRARED 101

Sir Frederick William Herschel used a prism and thermometers in his experiment that eventually led to the discovery of the infrared region of the electromagnetic spectrum.
Side-by-side view of a visible (left) and thermal (right) view of smoky forest scene

The easiest way to understand thermal radiation is to understand how Sir Frederick William Herschel discovered infrared radiation in 1800. Very basically, Hershel studied sunlight through a prism. We all know the visible light is broken into a rainbow. Put a thermometer on the colors, then put a second thermometer well past the red, and you will see the second thermometer's value rise. That is the “light” we see. It is the light past the red in the visible spectrum, or the infrared light captured by our cameras.

More basics: Everything always emits thermal, or infrared, radiation. You can't turn it off unless you are at absolute zero (-273 deg. C). You and everything around you are not the temperature of the sun, but modern cameras are sensitive enough to detect typical temperatures on planet earth, and have sufficient contrast to generate great images. Simple enough.

There are dozens of treatises about infrared imaging on the web. Everyone in the business loves to describe our science. But rather than write another story about thermal imaging, we will lean on our partner experts at DRS Technologies. They invented infrared imaging in the 1960s, and know more than most.

THERMAL VS. VISIBLE

From left to right: AF6, AF12, and AF24 – Three thermal image views of same airport scene using different athermalized lenses and FOVs (Images taken with Sierra-Olympics’ Viento 640 Camera).

Our eyes see visible radiation. Thermal imagers see infrared radiation, something entirely different. You can buy a great camera with 10 megapixels that will take snapshots and videos for $200. The smartphone is now the most popular form of camera, and its sensor costs a few dollars. Thermal imaging manufacturers aren't there, and probably never will be. We use exotic materials in our sensors that are not so common, our lenses are made from crazy materials like Germanium and Zinc Selenide, and we don't have billions of customers. If you have a problem where you need to locate heat or image heat, our cameras make it easy and affordable.

FUNDAMENTALS

Viento HD Lab camera, with the world's first “true” high definition thermal imager with a 1920 × 1200 × 12 μm uncooled sensor.

We should put some of the most basic technical items on the table. If you are approaching thermal imaging from an experience based upon standard visible imaging, allow us to get some preliminaries out of the way.

Resolution:

We have 320 × 240 (QVGA) and 640 × 480 (VGA) imagers. There are larger arrays, but they are exotic and expensive. In thermal imaging, you can get a 3MP imager from a big military contractor for a million bucks, maybe.

Cost:

There are billions of people on the planet, and most have a visible camera in the cell phone. Thermal imaging just does not have that large customer base to create a $200 snapshot camera, or a $50 web camera. But compared to where we were only a few years ago, we are very low cost.

Optics 1:

Compared to the selection of optics you see in the visible world, infrared optics are very limited. Glass is opaque to thermal radiation, so we must build optics out of exotics such as Germanium or Zinc Selenide or Sapphire. This makes optics expensive and limited in selection.

Flexibility:

High speed, windowing, triggers, binning, 3-CCD – functions commonly available in modern cameras are not available on our value priced cameras. You are back up to very high-priced cameras for these functions. Think $50,000 and up. Think $452 hammers and $640 toilet seats.

Optics 2:

With my SLR camera, I can pop one lens off and install another in seconds. You can't do that with thermal imaging. The camera and lens are designed together. When you install another lens, it doesn't work as well. There are procedures and tricks, but in general, one camera-one lens.

CONCLUSION:

We've seen the basic workings of thermal imaging in this brief overview. The applications for thermal and infrared imaging are broad and range from aerial surveillance and perimeter security, astronomy, military imaging and night vision, to automotive, law enforcement, medical and laboratory imaging, and from machine vision, inspection and other industrial tasks, to unmanned systems and more. With improved technology, manufacturing techniques, and lower costs, we're seeing more applications develop than ever before.

This article was written by Chris Johnston, President, Sierra-Olympic Technologies, Inc. (Hood River, OR). For more information, contact Mr. Johnston at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit Here.

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