Can a Thermal Camera See Through Walls?

October 09, 2019

Can a Thermal Camera See Through Walls?

Let’s face it, a thermal camera is a league of its own - outclassing even the most sophisticated of cameras in more ways than one. That can only mean looking into the essentials of the thermogram-producing device is key to unlocking its secrets. And to discerning, if the nifty device can see through walls. And beyond. One thing’s certain. Ever since its inception, its initial use in the U.S. military (e.g., Korean War) and in law enforcement, and its late adoption in firefighting in  20th-century America, the thermal imaging device has without a doubt produced groundbreaking results - eclipsing any point-and-shoot camera on the planet in revealing the unseen.

Small wonder why a thermal camera with its impressive resume is tasked to ‘see through walls’ - perhaps in the style of Superman, the fictional D.C. Comics iconic superhero. Surely, such an uncanny ability is a huge lift to make any home inspector worth his name in salt jump for joy.  But can it? To know that, we’ll have to do a paradigm shift. Looking at a thermal imaging device in the eyes of old-fashioned photography (the usual come-on to fill our social media accounts to the brim with an audience) is like putting a round peg in a square hole. It does not work. In this regard, here’s the nitty-gritty. Read on.


The Evolution of the Thermal Camera: Through Thick and Thin

Thanks to astronomer Sir William Herschel (1738-1822), infrared was discovered. Using a thermometer, Herschel, the astronomer whose claim to fame incidentally is his discovery of the planet Uranus, stumbled upon a dark region beyond the red end of the color spectrum produced by sunlight in his prism experiment, a replication of the much-ballyhooed testing done by Isaac Newton. To his surprise, the region under study was not only hotter than the rest but was also invisible to the naked eye.

Of course, we now call that spectrum as the electromagnetic spectrum. And we know that in that spectrum, temperature readings increase from violet end to the red end. Today, the thermal camera stands unchallenged as the foremost device to measure the presence of infrared light - aptly called ‘thermal energy’ - in various degrees.

Seeing the immense benefits, it did not taking long for the military to quickly pounce on infrared technology. A century or so later since Herschel’s experiment, thermal imaging was actively used in modern warfare - to gain a distinct advantage over the enemy. Some key milestones:

  • In 1929, an infrared-sensitive electronic television camera was used as part and parcel of the British anti-aircraft defense system.
  • Years later, not to be outdone, American soldiers made the most out of thermal imaging cameras during the Korean War (1950-1953).

Steadily, infrared imaging technology was getting lighter with the ultimate goal of being able to use it on the move. Just about anywhere.

And with thermal camera’s supreme ability to detect heat and all its intensity even with all the smoke, it was just a matter of time for the device to fall into the hands of firefighters in the American mainland.  For their part, the American Society of Non-Destructive Testing soon developed teaching standards for thermal imaging courses starting in 1992. Eventually, by 2006 prices of thermal cams fell through allowing home inspectors - amongst them HVAC and electrical experts - to use them professionally.

But what does a thermal camera actually do?

Thermal imaging camera, also known as a thermal camera, also known as an infrared camera or IR camera, renders infrared radiation as visible light. In short, these powerful devices detect heat. Specifically, they detect heat as it bounces off an object.

Naturally, a thermal cam does not need light to see what’s in front of it. Such a distinction speaks volumes on the essence of thermography - the detection of heat signatures using an IR camera. On the other hand, an ordinary camera like those we’ve loved to fiddle with as added gadgets on our smartphones is rendered blind in the absence of light.

By understanding its nature, it’s easy to come to terms with an infrared’s camera’s ability:

  • To see through the dark
  • To see through smoke
  • To check temperatures without touching anybody/anything

Of course, thermal cameras hit mainstream when Arnold Schwarzenegger fought aliens using thermography in his 1987 sci-fi flick Predator. Arguably, it was the first time a thermogram, or the picture results from a thermal cam, was in full display for everyone to see. Not only did that blockbuster movie light up the world’s imagination, but it also showed everyone how powerful infrared imaging is.


So can It Let You See Through Walls?

That is the one-million-dollar question. And the answer will get right back at us by looking at infrared’s unique characteristics. Looking into how infrared light behaves is paramount to unlocking the capabilities of thermography.

First up. When we use the language ‘see’, we are referring to the capacity of our eyes to view the world we live in. The mountains, the leaves, etc. We love old-school cameras as they give us an exact - if not better - rendering of the world around us. A world dependent on light to be seen.

But a thermal camera does not work that way. It does not see as our eyes can see. Instead, it detects heat around it - individualized as heat signatures. So when looking at a thermograph, the picture produced by thermal imaging, you see colors representing various thermal energy in its environment.

What the thermal camera see therefore is not how an ordinary camera would see. In its world, objects are defined by how much heat energy it is emitting. Thus, it can only register thermal energy bouncing off an object in front of it.   

So when scanning a wall, a thermal cam detects the heat bouncing off that wall. The surface temperature changes of the perpendicular barrier so to speak. So if something so hot, like fire, is behind that wall, the heat of that fire will register on that wall. And the thermal camera will see it. The heat caused by that proverbial fire would be seen on the resulting thermograph.

Strictly speaking, infrared is capable only of detecting the heat signatures of the surfaces in front of it. So the answer to that layman’s question is a resounding NO. That’s only because the question is posited from the POV (point of view) of seeing as humans would.

From the perspective of the thermal camera, however, we can say it can see through walls. And the answer is YES. That’s because it can detect heat behind the wall that’s affecting the wall. Again, this is in reference to the fact that heat is the language of thermography. And not the beautiful sceneries we look for in a traditional picture.

A deeper question is: Can infrared radiation not go through walls like the X-ray vision of Superman would?

We must remember that thermal imaging systems also have their range. Not all thermal cams are created equal. Just like ordinary old-school cameras.

Generally, commercially-available thermal cameras operate on two fronts:

  • Long-wave infrared (LWIR) and
  • Mid-wave infrared (MWIR)

We’re talking about 3µm to 14µm wavelengths in the electromagnetic spectrum. MWIR spectrum is at 3 to 5μm in wavelength while LWIR is at 8 to 14μm in wavelength. And this is but fitting as most, if not all, objects on the planet emit their heat in these ranges.

The hotter an object gets, the more it puts out electromagnetic radiation or EM.

The thing is walls serve to block these wavelengths. So when you point a thermal camera at a nearby wall, the device reads the heat emission from that wall. And not behind that wall.

You may be able to detect the heat behind the wall when that heat is affecting that wall, imprinted on its heat signature.

On the same analogy, glass won’t register anything on a thermal camera’s readings. It’s plain opaque - usually, that is. Why?

Simply because glass, at least most of those we encounter on a day to day basis, transmit heat below 3μm in wavelength. A range far below a regular thermal cam’s normal range.

Thermal radiation within or surrounding a body is also called black-body radiation. This is a highly-technical term that involves an object’s thermodynamic equilibrium with its environment.


To Wrap Things Up

Does a thermal camera see through walls? The answer will depend on what kind of picture you want. Your POV, so to speak. From the perspective of producing a picture of the objects, the same kind picture you keep on your smartphone as memories, behind that wall, it would have to be a NO.

Bear in mind, however, that at its essence an infrared camera sees only heat signatures. Unlike an ordinary camera. So if the question is rephrased to: Can a thermal imaging device see the heat behind a wall? And the answer is it’s entirely POSSIBLE. So long as that heat signature is strong enough to affect the surface temperature of that particular wall.

Again, all these emphasize how a thermal camera has made a huge dent in our daily lives - wall or no wall.