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Not too many of you guessed this week–was it a tough one? If so, check out the answer below:
 Infrared Image  Visible Light Image
 Picture-in-Picture (Infrared PIP) Image Answer: Image is of a sub-floor heating system! This week, we also included a picture-in-picture image that includes both visible light and infrared, helping you more easily identify and report problems. Fluke thermal imagers can be a useful tool in determining if these systems are operating properly and according to design.
Nice job, Steven, for guessing correctly! And thanks to our very own Michael Stuart for supplying the images. Hope you enjoy the infrared teaser images to come 
I often joke that were it not for emissivity, you’d not need training to use an imager! In our courses we find emissivity is the #1 most confusing issue for people, whether they are engineers, home inspectors or new thermographers. In fact, we all usually have a good laugh that many cannot even pronounce the word. So if you also feel this way about the term or the concept, you are in good company!
Emissivity describes how to quantify the efficiency of a surface for radiating energy in a defined waveband and at a given temperature. Reality says any surface above absolute zero will always radiate some energy (more than 0%), and no surface can radiate perfectly (100%).
When considering infrared radiation most shiny metals emit inefficiently. This means they don’t tell us the thermal truth about themselves! Most non-metal surfaces—paint, paper and human skin, for example—are much more efficient emitters, so it is easy to make a direct connection between what they radiate and their surface temperature. Remember the hot frying pan?
Emissivity values can be determined or measured by engineers. Be aware, however, they are very specific to the material type, surface condition and, especially for metals, the temperature of the material. We can use the values not only to help us understand how a surface might behave but also, in some cases, to correct our radiometric measurements.
 A single image often contains many surfaces each with a different emissivity and, as is the case here, with different temperatures. Making accurate corrections for high-emissivity surfaces, like the hand, mug and the water, is fairly straightforward, but the low-emissivity metal spoon is very challenging to work with—more on that next week! Thinking of these values as percentages may help. Human skin, with a value of 0.98, is 98% efficient at emitting thermal radiation while shiny aluminum, with a value of approximately 0.10, emits only 10% of the energy. When we input these values into our imagers, they automatically correct the raw data that had assumed 100% radiation was emitted based on the surface temperature.
As you can imagine measurements using extreme corrections, as are necessary for bare metals, often are unreliable and that is why we strongly recommend making measurements only on surfaces with values greater than approximately 0.6. On metals, the simplest way is to add a high-emissivity “target” of paint or electrical tape.
When you input a correction, the resulting changes are made to the entire image. Obviously, because of this fact, separate corrections must be made for each different point we want to measure. While some models allow these corrections to be made in the imager itself, the good news is they can also be made in the software to a stored image. All changes can be undone or “tweaked” to better match reality.
I’d encourage you to practice making measurements on various surfaces that are at least 10oC (18oF) warmer or colder than the surroundings—windows, coffee cups, skin, etc. Compare what you measure on the surface with what you measure on a high-emissivity target (use electrical tape with an emissivity correction of 0.94). Notice, too, what happens as you adjust the emissivity correction for these surfaces—the image doesn’t change, but the corrected temperature values do! Next week we’ll talk about what is being reflected from the surface and how to correct for that.
Don’t expect everything to become crystal clear immediately, but you should quickly find out emissivity is not as confusing as it may have seemed to be. Here are two good guidelines:
- Radiometric temperatures of bright metal surfaces will be unreliable. Use high-emissivity targets whenever possible.
- Radiometric temperatures of nearly all other surfaces in nearly all instances will be quite reliable.
Thinking Thermally,
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner
Fluke’s own, Michael Stuart, provides a hint for today’s teaser infrared image: “Oh…that toasty feeling!”
Leave your answer in the comment section, and check back on Thursday for the answer!
Seems like you guys definitely know your ball park food…
 Infrared Image
 Visible Light Image
Answer: Image is of a (as Dan said) “hot diggety” dog! As you can see, this thermographer decided to do more work during his lunch break.
We hope you enjoyed figuring out this week’s teaser infrared image as much as John enjoyed eating it: “It was thermal and by the way, it was good!!!” —John Pratten
In life we often make corrections to our first impressions or first courses of action. Whether we are following directions while driving, stepping on the scale to check our weight or adding cream and sugar to our coffee, corrections are an important part of getting it right! Without them, we don’t get to where we were going, we weigh too much (never too little!) or the coffee just isn’t right
For thermographers, making corrections to our radiometric measurements is just as essential as making sure the driving directions actually get us where we wanted to go. Why can’t these high-tech instruments get it right? Because we are not actually measuring temperatures! We are, as a matter of fact, measuring the radiation emitted from, reflected by or coming through a surface.
 How do we measure radiometric temperatures accurately? We must make corrections! In many situations that will get us within ±2ºC of reality—not bad for work being done before we’ve even had our first cup of coffee in the morning. The imager sees all the sources simply as radiation and converts that sum total into an apparent temperature. Unfortunately, only the emitted energy is related to surface temperature. The reflected and the transmitted energy tell us nothing about the actual temperature. It is not unlike walking up to a plate glass door and being confused about the reflections that overlay the scene we see through the door—unless we correct for this reality, we may bump into the door!
If all this sounds complex, it is! In fact, the whole 4-day Level II course is essentially spent on these and related issues. The reality of our work is that without corrections, most measurements would be inaccurate—nearly all just a bit off but many others far enough off the mark to make us wonder if thermography works at all!
Too many thermographers don’t grasp the basics of corrections for emissivity, reflected temperature and, in some important situations, for transmission as well. Often we hear of people simply ignoring emissivity corrections, or failing to understand background corrections or, poor souls, having no idea how to make a measurement through an infrared window!
While temperatures are not always the most important detail, they are often a useful part of our analysis and we need to know how reliable they are. Our goal is to simplify reality so we can make measurements, with appropriate corrections, that will be within ±2ºC of reality for many situations. That is a cup of coffee worth enjoying to the last drop!
We’ll spend the next several weeks discussing these corrections in detail so you can feel more confident in your work. You’ll know when you are able to get measurements that are reliable, how to get them and, most importantly, when measurements will be unreliable despite the corrections.
Thinking Thermally,
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner
We really enjoyed serving up this weeks “tasty” thermal image… Can you guess what it is?
Leave your answer in the comment section, and check back on Thursday for the answer!
Was this week’s infrared image a tough one to crack? If anything, we hope you thought it was “cool”…
 Infrared Image
 Visible Light Image Answer: Image is of ground frost exposed following the pass of a backhoe! This infrared image was taken during the Spring, and shows a thawing pattern near the surface, but also clearly shows the frost below the surface. Needless to say, this infrared image is definitely an interesting one, and out of ordinary, so we hope you enjoyed it!
And Dan, you were right on with your ice cube guess—just a really big ice cube! Thanks for your constant participation.
Come back Tuesday to try and guess next week’s teaser infrared image
Whether we work outside or inside, day or night, inspecting buildings or substations, we must learn to deal with the Sun because it is very powerful.
The sun radiates both long and mid-way infrared electromagnetic energy, but it also radiates considerably more energy in other parts of the spectrum—ultraviolet, short-wave IR, visual, and radio—that, when absorbed, cause materials to heat up. Full spectrum sunshine, as it is called, has significant heating power when absorbed by any material.
The classic example is that dark surfaces absorb more than light ones, as is the case of the Think Thermally™ t-shirt hanging on the clothesline—but it can be much more involved than that. The rate at which sunshine is absorbed (or transmitted or reflected) is often different than the way long-wave infrared alone behaves. As thermographers, we sometimes fail to appreciate that fact.
A thermographer’s life in an outdoor substation on a sunny afternoon—summer or winter—can be challenging. With long-wave imagers, reflections are not a problem, but solar loading can be. A brown insulator is hotter than a grey one—is it a problem or just the effect of the sun?
A weatherization specialist looks at a home on a bright, but overcast, winter day and is amazed that the light trim is so much cooler than the dark body of the house. She could even see where parts of the wall had probably been in the shadows before she arrived. Inside, she is stunned to find the walls appear to be uninsulated when she knows otherwise. Armed with patience and her Level I skills, she reasons out that the sun has caused a reversal of the normal winter direction of heat transfer!
 Even with the winter sun behind the clouds, this house shows the cooler shaded areas and the affect of the sun on the dark paint (and light trim). Inside, the sun has caused the direction of heat flow to reverse so an insulated wall shows up as cooler. It is not unusual to see these effects even 4-6 hours after the sun has been on a wall. We need to always pay attention to the sun—where it is and where it has been, what has been in the shadow and how it is absorbed. The sun is not a thermographer’s “enemy,” but it can be a significant “pain” at times. However, it mostly just makes life more interesting and can even be an “ally” in some instances. We simply need to understand how it affects us and work with it.
Next week, we’ll begin a series on radiometric measurements—emissivity, background temperature, resolution and transmission. Imaging alone is great, but adding in the temperature values makes this technology much more powerful.
Thinking Thermally,
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner
“Chill out” while you ponder this week’s Teaser Infrared Image…
Leave your answer in the comment section, and check back on Thursday for the answer!
I guess this week’s infrared teaser image really “sucks” (literally)… Bad joke?
 Infrared Image
 Visible Light Image Answer: This week’s image is of a vacuum system! You can see above that as air is compressed, it increases in temperature. Of course, the infrared camera would help show if the system isn’t working properly when compared to the baseline image.
Thanks—as always—for all your guesses, and keep ‘em coming!
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