Introduction:
Step into the realm of the hidden, where the unseen dances into view like magic. Thermal imaging, a wizardry of modern science, unveils the invisible cloak of the infrared spectrum. Equipped with specialized cameras and technological enchantments, it reveals the secrets of the unseen world that envelops us.
As a Certified ITC Thermographer, I possess the keys to deciphering the cryptic messages embedded within these ethereal images. Within this clandestine domain lies a treasure trove of revelations, waiting to be unveiled.
After all, what is thermal imaging? What is infrared thermography? We’ll answer all of that and more, just keep reading.
In the last several years, we have seen thermal imaging technology not only become more affordable but more accessible as well.
It’s hard to believe that we’ve come so far since the first thermal camera systems were developed in the late 1920’s.
The first thermal cameras were big and bulky. One of the first portable thermal camera systems developed required a truck to move it around so it could be used.
Today we have thermal cameras so small they are able to fit onto our drones.
As of this writing, that is not the case with the standard Mavic 3 or the Mavic 3 Cine variation.
History of thermal imaging:
Thermal imaging was first discovered by astronomer Sir William Herschel in the year 1800, who at the time was trying to devise a filter through which he could reduce the sun’s glare when observing it through a telescope.
Without adequate filters, severe eye damage was possible, even after just a few seconds of exposure looking through the lens.
In his experiments, he used a red filter, and this seemed to produce a lot of heat.
In order to measure just how much, he passed that sunlight through a prism while holding a thermometer positioned just beyond the red end of the visible spectrum.
He noticed that the thermometer registered a temperature that was higher than the ambient air in the visible spectrum and concluded that there was another form of light beyond what could be seen by the naked eye.
Herschel had discovered the Infrared Spectrum. Herschel dubbed his discovery the “thermometrical spectrum” but sometimes called it “the invisible rays” and occasionally “dark heat.”
Today we refer to this as the infrared spectrum, and it is an extension of the Electromagnetic Spectrum. The term infrared came into use in the early 1900s.
The next major advancement came in 1840, when Herschel was able to produce thermal images that were printed on paper for the first time.
Herschel called this a thermograph, and that term has stayed with us till the modern day and has a deviation that is in use called a thermogram, meaning a thermal image.
You may still see the term thermograph used on some occasions.
The next large advancement in thermal imaging was the bolometer in 1880, which is still what makes our modern thermal cameras today possible.
Every thermal camera today will have a bolometer within it.
The bolometer was Invented by the American astronomer and physicist Samuel Langley. The bolometer is a precision instrument that could accurately measure the infrared radiation given off by an object down to 1/100,000 of a degree.
The first actual infrared camera was built in 1929.
It was a motion camera used by the British army for anti-aircraft operations following WWI. The military adopted the use of infrared cameras quickly, and soon the technology was a vital part of defense strategies around the world.
What is thermography:
Infrared Thermography is the process of acquisition and analysis of thermal information from non-contact thermal imaging devices.
For those of you out there who may not be familiar with an infrared image, here’s a quick explanation to help you understand what it is.
In a thermal image known as a thermogram, the darker areas are those that radiate less thermal radiation, and that generally means that those areas of the target are cooler.
Brighter areas mean the opposite – more thermal radiation and a possibly warmer target.
As we can see from the above image, the roof is cooling due to the thermal load being removed. Imaging was captured 2 hours after the sun set.
In this case, the thermal load was the day’s sunlight. A thermal load can be anything that generates heat onto the object.
We also see that there is an area of the roof that is retaining heat and dissipating at a different rate from the surrounding area. The area starts from about the mid-point of the valley and extends across the roof.
This clues us in that there is something anomalous with that area. Upon further inspection, it was determined that water was penetrating under the shingles from the valley.
This roof was a good example of a failure as we can also see there is a failure along the ridge top as well, and we are able to track the presence of water and its path.
The light green areas are water under the roof since water cools at a different rate compared to the areas around it.
In this thermogram above, we see multiple failures of the roofing system again, mainly from the ridge cap and around the fireplace chimney flashing.
Sadly, both of the above images represent the same roof.
The end result was the clients got a new roof, they were able to present multiple failures to their insurance company and they made the contractor redo the work.
The initial roof was replaced due to storm damage, and we are looking at the replacement.
This roof was only three months old at the time the imaging was done and revealed the roof had been improperly installed, with water making its way into the interior of the home in several places.
This is just one of the many uses for thermal technology.
The above images show a Single-ply commercial roofing system. In this example, the thermal shows that the roof is intact and that there appear to be no anomalies.
In the matching RBG image, we see there is pooling in the corner of the roof but no penetration of the layer as of yet by the pooling water in that area.
Visual vs. Night Vision vs. Thermal Imaging:
It’s easy to see that there is little relation between a visual image and a thermogram, as shown above in the matching images.
Primarily though, the biggest difference would be that a visual image requires color absorption and reflection to create the image as well as light, whereas a Thermal image (thermogram) is unaffected by light sources and can still be taken even in the complete absence of light.
This is because a thermogram detects the emitted heat and creates an image from that information.
There is a big difference between Night Vision and Thermal Imaging, although the two often get confused with one another.
Night Vision is the use of amplifying small amounts of available light and requires some light to be present to work.
As we’ve just covered, thermal imaging requires no light at all to operate and can be used either during the day or in the dead of night.
Uses for thermal imaging:
Thermal imaging is used in many industries today, from electrical systems, to home inspections, to cell towers, search and rescue, and many more.
One of the benefits of thermal imaging is that it is capable of seeing through smoke.
For firefighters, this is an invaluable tool to identify hotspots and even people trapped within a fire situation.
These cameras are used to monitor mechanical equipment in factories to verify that it is operating within its proper operational temperature.
In the gas industry, these systems are employed to monitor tank levels and possible leaks or missing insulation on piping in the system.
They are even used to identify Geothermal activity.
The uses are simply too numerous to list here, with these just being a few examples.
One of the biggest benefits of using thermal imaging is that it is non-contact. This is important say in inspecting electrical systems when the live components simply can’t be touched.
Thermography does not intrude upon or affect the target at all and is one of the only non-contact methods we have.
How to use a thermal camera:
Using a thermal camera requires some specialized training, not only to operate the camera itself but to analyze the image and be able to interpret the data.
Thermal cameras are not like regular cameras you may be familiar with. In order to capture a good readable thermogram, certain information needs to be entered into the camera prior to use.
To capture a thermal image that you can properly analyze:
- The thermogram must be in focus
- It must be taken in the correct temperature range
- You must be close enough to the target
In Thermography, we use FORD (Focus, Range, and Distance); the parameters of FORD are those that cannot be changed in post-processing software and so are critical to get right before taking and saving the image.
One of the most important factors in capturing a good thermogram is knowing the object’s Emissivity. If you’ve never heard that term before, I wouldn’t be surprised.
The emissivity, ε, of the surface of a material is its effectiveness in emitting energy as thermal radiation and varies between 0.0 and 1.0.
As shown here below in the chart, everything has its own emissivity, and this will play a big part in whether you capture an in-focus and tuned thermogram or not.
Much like FORD, emissivity has to be entered prior to capturing a thermogram and cannot be adjusted in post-processing.
Emissivity is the single most important attribute necessary for accurate thermal measurement, and yes, it is that important.
Conclusion:
Thermal imaging is an important tool in our toolbox. With it, we can broaden our view of our world to the unseen and make it visible.
Companies like FLIR and Fluke are working diligently to bring the cost of these systems down and improve their abilities.
I know we covered quite a bit here in this article, but not nearly everything.
There are many more aspects of thermal imaging still left for you to explore, whether it’s the fundamentals of IR Science or the many other facets in between, such as the Stephan-Boltzmann equation, to heat transfer and so on.
Just know that a thermal camera is not like any other camera you may operate, and knowing how to operate it properly does require additional knowledge and training.
Not just for using the camera itself but being able to read and analyze the data that was collected by it.
You just never know what may be revealed to you from that hidden world, so go have a look. You’ll see!
