Home Optics Thermal Imaging 101: What It Is and How It Works?

Thermal Imaging 101: What It Is and How It Works?

Pulsar Core FXD50
Pulsar Core FXD50

“Hey check these out,” my friend and fellow Marine said as he handed me a small monocular. It looks a bit like our PVS 14-night vision devices, but smoother, rounder, and a little larger. Putting it on filled my view with a bright black and white picture. I scanned, seeing a world that was usually hidden from my eyes.

In many ways I saw more than I ever could with normal night vision. What I was handling was a thermal imaging monocular. This was something I had never used before but I immediately fell in love with it.

You couldn’t sneak up on me if I were using a thermal optic. I could see the world moving around me: dogs, farmers, other Marines in vivid bright white blotches complete with decent detail.

thermal scope on rifle

I had heard of thermal optics but never used them, and I was instantly sold. Before the deployment was over, I was issued my thermal scope and put it to use as much as possible. Thermal imaging captured my imagination, and I wanted to find out how this magic worked.

It all starts with the world around you. Everything in the world emits heat. Heat is an infrared energy that is detectable with the right technology. Thermal imaging units register heat and turn it into a visual picture.

This allows users to detect heat, which can be invaluable to soldiers, Marines, police officers, and even in some construction industries.


How does Thermal Imaging Work?

But how does it all work? That’s the magic question.


ATN BinoX-THD 384 Thermal Smart HD Binoculars
ATN BinoX-THD 384 Thermal Smart HD Binoculars


Light is a tricky thing. It comes in spectrums, some you can see, and others you can’t. Infrared light is invisible to the human eye, and it comes in three different categories: Near IR, Mid-IR, and Thermal-IR.

Thermal IR is what we are most concerned with, and it occupies the most significant part of the infrared spectrum.

Thermal IR is the only type of IR that an object generates instead of reflecting it. The hotter an object is, the more infrared it produces. A thermal device can see the infrared light and then turns it into an image.

It does through a complicated and technical device that has a particular lens. This lens is not made of glass because glass can block long-wave infrared light; instead, they are made from germanium or sapphire crystals. Every thermal device out there has a thermographic camera in it.

This thermographic camera has a ton of tiny devices that measure and capture infrared radiation. Every pixel in a thermographic camera has one.

thermal imaging process

These devices sense the heat in great detail and turn it into a picture you can see. This is called a thermogram. These cameras are so well made that they do all of this in roughly 1/30th of a second.

The thermogram is taken and turned into electric impulses. These electrical impulses are then tossed into a signal-processing unit. This is a circuit board with a particular chip that acts as a Rosetta stone for electric impulses.

They translate the electrical impulses into a display, and that same signal processing unit sends the information into the display. That display is usually many different colors representing different levels of heat.

The hotter an object is, the brighter it will glow. This allows you to see your target in finer detail and will enable you to distinguish between different moving objects.

Like standard night vision devices, thermal imaging devices do not offer you a lot of high definition picture or many colors. The tech just isn’t there yet. The colors you see aren’t the actual colors you’d see in normal lighting conditions; they are just colors assigned to the device to show different levels of heat.

Thermal Image of Human Body

This generates a picture that allows you to spot differences in the dark standard night vision can’t do.

There are thermal binoculars, thermals monoculars, thermal weapon scopes and more, but in general, there are two types of thermal imaging devices—well, two categories I should say.

The two categories are uncooled and cryogenically cooled:

Uncooled options are the most common type of thermal imaging technology. These are small, handheld, and function well for most uses. The infrared detector elements are kept at room temperature. They turn on instantly, have a built-in battery, and are silent.

Cryogenically cooled thermal devices are incredibly expensive and quite fragile. They are easy to damage, and their cost means that they should be used with caution. These devices are sealed and have elements in the container that cools them to zero degrees Celsius.

With these systems, you get a super sharp and clear picture and the ability to see insanely fine changes in temperature at extremely long ranges.


How is Thermal Imaging Different than Night Vision?

thermal vs night vision
Thermal vs Night Vision view

Thermal imaging is most commonly used at night, but it doesn’t need to be night vision. It can be used during the day, and often is in security applications. You’ll find it in airports, for example, scanning people in bright daylight.

Thermal imaging doesn’t give you the details that standard night vision will provide you with. With standard night vision I can see a person, and even their facial features. The image offers overall more details. Thermal imaging is better suited for finding people who are hidden and/or camouflaged.

Read our full thermal vs NV comparison article…


Who Uses Thermal Imaging?

firemen using thermal imaging

Soldiers and Marines, of course, use thermal imaging in combat scenarios. They allow men on guard to quickly detect a potential threat, or to monitor a target and conduct surveillance. Police officers often use it for the same tasks when it comes to surveillance.

Police also use them to search for escaping felons and are often attached to helicopters. These large systems are invaluable to police work.

Additionally, thermal imaging units are used by firefighters to find and see through smoke in homes and even during wildfires. Construction companies and inspectors use them to detect potential threats as well as to ensure the safety and compliance of certain systems.

Thermal imaging is very unique and fascinating as a technology. It’s invaluable for a variety of roles and can be used for everything from combat to search and rescue. Most civilians use them for security purposes and hunting, and they work well there too.

We hope you learned a thing or two today, and if you have any questions, just ask below.

Make sure to also check our article on how to sight in your thermal scope.



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