Thermal imagers are altogether different. In fact, we call them “cameras” but they are really sensors. To understand how they work, the first thing you have to do is forget everything you thought you knew about how cameras make pictures.
FLIRs make pictures from heat, not visible light. Heat (also called infrared, or thermal, energy) and light are both parts of the electromagnetic spectrum, but a camera that can detect visible light won’t see thermal energy, and vice versa.
Thermal cameras detect more than just heat though; they detect tiny differences in heat – as small as 0.01°C – and display them as shades of grey in black and white TV video. This can be a tricky idea to get across, and many people just don’t understand the concept, so we’ll spend a little time explaining it.
Everything we encounter in our day-to-day lives gives off thermal energy, even ice. The hotter something is the more thermal energy it emits. This emitted thermal energy is called a “heat signature.” When two objects next to one another have even subtly different heat signatures, they show up quite clearly to a FLIR regardless of lighting conditions.
Thermal energy comes from a combination of sources, depending on what you are viewing at the time. Some things – warm-blooded animals (including people!), engines, and machinery, for example – create their own heat, either biologically or mechanically. Other things – land, rocks, buoys, vegetation – absorb heat from the sun during the day and radiate it off during the night.
Because different materials absorb and radiate thermal energy at different rates, an area that we think of as being one temperature is actually a mosaic of subtly different temperatures. This is why a log that’s been in the water for days on end will appear to be a different temperature than the water, and is therefore visible to a thermal imager. FLIRs detect these temperature differences and translate them into image detail.
While all this can seem rather complex, the reality is that modern thermal cameras are extremely easy to use. Their imagery is clear and easy to understand, requiring no training or interpretation. If you can watch TV, you can use a FLIR thermal camera.
