Did You Know? How Surface Structure Effects Accurate Temperature Readings
You shouldn’t judge a book by its cover but when it comes to getting accurate IR temperature readings it’s all about what’s on the outside. So for instance, if you have a stainless steel pipe that is running at 100 °F and a flat painted pipe also running at 100 °F, which one will appear to have a higher temperature? If you said the painted pipe, you would be correct but you also might wonder why you were correct. There are several things that effect accuracy but we’ll just look at one: Surface Structure.
Let’s get one thing out of the way right off the bat; emissivity is the single most important factor for reading apparent temperature. So what is emissivity? Simply put, it’s the amount of energy emitted by an object. Some materials have a high emissivity, rough surfaces, painted surfaces, non-metals; these will all tend to emit a more accurate picture of their true temperature. You could say they’re an open book, what you see is what you get.
Now in contrast, glossy materials (like the stainless steel pipe) are not very good emitters because their too preoccupied with being good reflectors (no one can be good at everything) and therefore they may give you a better idea about the temperature of things around them than their own temperature.
What’s the main point? If you’re going to take a reading on a highly reflective surface you need to either compensate for that in your camera i.e. adjust the emissivity settings, or place something that is a good emitter on the surface and then take the reading. Electrical tape has an emissivity of about .95 which makes it a handy tool to keep around. Just slap it on the surface and you’re good to go. Another thing you can do is find an area with lots of corrosion which is also a good emitter and use it for your thermographic exploits. Just remember, with thermography, it’s what’s on the outside that really counts.
That’s all for today, now get out there and soak up some infrared radiation!
Looking For Life In All The Right Places
“Turn left.” It was an early April morning and the area had been seeing copious amounts of very persistent rain. One of the things you learn about driving anywhere in southern Indiana is to take instructions from your GPS with a healthy dose of skepticism and a complete lack of gullibility. As the van lights swung to the left revealing nothing but inky black water it was obvious that we would need a different plan.
After a bit of finagling we found a road that didn’t require the poor van to have amphibious abilities and arrived at our spot, a very, very small parking lot on the east of a not so little pond. Our mission (since we chose to accept it) was to test the abilities of our FLIR XT Infrared camera mounted on the M600 drone and spot muskrats along with other aquatic and non-aquatic animals in their native habitat. With our strobe light in place and nighttime waver in hand we prepared to observe the infrared animal kingdom from 200 feet above the water.
The View From Above
We achieved lift-off without a hitch and ascended slowly as the strobe winked away reassuringly from the underside of our aircraft. I turned the dial on the remote and the gimbal motors smoothly spun the camera to take aim at the unsuspecting water below. Suddenly an entirely new dimension opened up. Four Grebes were darting through the water looking like a tiny squadron of fighter jets. The disturbed water behind them looked kind of like fluffy contrails in the sky. Then, as if on command, one Grebe and his trail completely disappeared only to reappear about 30 feet later. That’s impressive diving abilities in my book.
The show continued for about an hour and while we didn’t find any muskrats, we could easily pick out a variety of birds and other little creatures going about their day, happily oblivious to the 6 rotor paparazzi bird that was snapping pictures and capturing videos of them.
The drone landed without incident and as we packed up and made our way back through the labyrinth of flooded back-ways to the main road it was with a renewed appreciation for how valuable drone based Infrared Thermography can be in wildlife management. The data acquired was solid and the disturbance to our water loving friends was minimal. The sun was starting its own ascent for the day and illuminated the flooded landscape. It was a subtle reminder of how this technology can also be used to save the lives of both flood victims and missing people. It had turned out to be a day of discovery, in more ways than one.
Different Color Palettes, It’s Not Just About Looking Pretty
There’s no way around it, looking at the world through an infrared camera is cool, really cool. Even just looking at hot water coming out of a faucet feels like you’re watching molten lava pour into the sink and down the drain. Of course, what you’re seeing is just a representation of the infrared radiation and that representation can be dressed up in different color schemes depending on the situation and your preference.
While not all cameras have exactly the same options, here’s a brief rundown of three FLIR color palettes.
This is the original palette used with IR (Infrared) imaging systems and it’s still a favorite for many thermographers. The focus tends to be a little clearer and it’s great for seeing fine spatial detail. However, as you can see in the picture, it’s not as good for easily spotting small temperature differences.
Ironbow is a good, popular, all-around usage palette. It has a nice balance between spatial detail and thermal detail. Small temperatures will show up more readily and it has a nice intuitive appeal for non thermographers.
Rainbow High Contrast Pallet
As its name suggests, the rainbow pallet introduces more colors into your picture. It’s great for showing maximum thermal contrast and highlighting potential problems for a customer.
So in the end, color palettes are a very useful tool. Use them in real time during inspections, or in post processing and when generating reports. Use a variety and choose the one that’s right for:
1. The type of inspection
2. Personal preference
3. The needs of your customer
How To Identify Thermal Anomalies
A thermal anomaly is a fancy way of saying that there is a noticeable temperature difference. You may not know why, or even if it’s a problem, but you know there’s a difference. The problem is, sometimes things that seem to be anomalies are really just thermal reflections. You can think of it this way, if you were trying to shoot a video of a person looking in a mirror where would you stand? If you stand directly behind them your own reflection is going to end up in the picture, so you would need to stand to one side. Problem solved.
Something similar happens when looking at infrared radiation. Stand directly in front of what you’re scanning and your own thermal reflection will show up. Another big thing that can throw you off is the sun. In this video you can see two things that might seem to be anomalies but as the drone moves you’ll notice one “hot spot” moves with it. That’s the sun. The area that stays consistent as we move is the anomaly.
So it’s really a very basic concept. If you think you’ve found something out of the ordinary just move a little, take the reading again and see if your getting the same results. It’s also good to keep in mind that certain surfaces are going to be more reflective than others, meaning your not getting the full thermal story when you look at them, instead your seeing more reflected radiation than the object is actually emitting. Long story short: don’t be afraid to move your feet (or your drone) to get a more accurate reading and take into account the surface properties of whatever your looking at.