What is a thermal imager and how do thermal imagers work?

Thermal imagers are imaging devices that detect emitted infrared wavelengths.  Simply put, all objects that are above absolute 0º constitute molecular movement.  This molecular movement produces energy or “heat”.  The heat is emitted not in the visible spectrum but in the infrared spectrum, which is invisible to the human eye.  Thermal imagers detect this emitted infrared energy and process the information electronically into a video or “visual” image so that we can “see” the emitted energy.  Thermal imagers allow us to see objects in total darkness, see heat signatures left by hand or foot prints and many other scenarios that we would not be able to normally “see” in the visual world.

Is a thermal imager and F.L.I.R. (Forward Looking InfraRed) the same thing?

Thermal imagers are forward looking infrared devices.  The F.L.I.R. acronym was generated by our US military where this technology was first utilized.  Some of the first thermal imagers were mounted on the front on reconnaissance aircraft, hence the name forward looking infrared or F.L.I.R.

Why is it that I can see in total darkness with a thermal imager and not with any other imaging device?

Thermal imagers do not detect visual light wavelengths.  Thermal imagers detect emitted energy that is present in the infrared wavelengths.  Since thermal imagers do not detect visual light wavelengths they can operate in total darkness and provide imagery from all objects emitting energy.  All other imaging devices require some amount of visible light in the scene in order to generate an image, therefore, all other imaging devices do not work in total darkness due to the absence of visible light wavelengths.  This is sometimes difficult to grasp in that we as humans are conditioned to “visualize” everything based on reflective light.  The human eye can only “see” anything that is a result of reflective light in the visual spectrum.  We cannot see a hand print on a wall visually but a thermal imager can see the heat signature left by the human hand on the wall giving us an image of the hand print in a visual format.

Does a thermal imager work like a video camera?

Yes.  Video cameras use a detector that is sensitive to the visible light spectrum.  Electronics process the information gathered on the video camera detector into a “video” signal that we can view on a standard video monitor or display.  Thermal imaging detectors are sensitive to infrared wavelengths.  Again, electronics process the information gathered on the thermal imaging camera detector into a “video” signal that we can view on a standard video monitor or display.

How is thermal imaging and night vision different?

Night vision or Image Intensified devices require some light, starlight or moon light, to effectively function.  A night vision device acquires what little light is available from the moon or stars and amplifies that light to allow the user to see at night.  If there is no light available then the night vision device will not work.  Only a thermal imager can see in absolute darkness.  Night vision devices are affected by weather related obscurants such as snow, rain, blowing sand and fog as well as smoke.  Under these types of conditions, night vision devices are unable to perform.  Thermal imagers can perform exceptionally well in adverse weather conditions due to the fact they do not rely on light but rather emitted energy.  The infrared wavelength can penetrate smoke, rain, snow, blowing sand and most foggy conditions.

Do thermal imagers see through smoke, dust, fog, blowing sand, rain and snow?

Because the infrared wavelength is longer than the visual light wavelength, thermal imagers can detect emitted energy through smoke, dust, fog, blowing sand, rain and snow.  Visible light wavelengths bounce or are reflected of the obscurant particles due to the wavelength being short.  The long wavelength of the infrared spectrum can pass through obscurants allowing a thermal imager to detect the emitted energy.

Do thermal imagers actively emit any thing or are they totally passive?

Thermal imagers are totally passive in nature.  This means they do not “emit” any kind of wavelength, they only “receive” infrared wave lengths.  This means they cannot be detected by other types of covert devices.

What is the difference between an IR emitter camera and a thermal imager?

An IR emitter camera uses near IR wave lengths to “illuminate” a dark scene.  Since the “near” IR wave length used is not in the true infrared spectrum it has to rely on the visible light spectrum to be effective.  IR illuminators actively project the near IR wavelength on a dark scene.  A visual CCTV camera fitted with a special near IR filter can “see” more effectively in dark scenes.  IR illuminators are limited in their effective working distance and do not see through weather related obscurants or smoke.  IR Illuminators also have a short mean time between failures.

What is the difference between cooled and uncooled thermal imagers?

The difference between cooled and uncooled thermal imagers is how the actual thermal detector is stabilized to allow for effective detection of emitted energy.  Originally, all thermal imagers were cooled.  The detector on a cooled thermal imager is actually cryogenically cooled to sub zero temperatures using a very small condenser and compressor.  Since the detector is so cold, its sensitivity or ability to detect emitted energy is very good.  Some cooled cameras can detect human activity from 20km away.  Cooled cameras are very costly and require yearly maintenance for re-calibration.  They also have a mean time between failures of 2500-8000 hours.  Uncooled thermal imagers electrically stabilize the detector and do not require any cooling.  Years ago uncooled detectors did not have the sensitivity or range of a cooled camera.  Technology has advance with uncooled detectors so that they are almost as sensitive and are very close to the range of a cooled camera.  Uncooled thermal imagers do not need periodic maintenance for re-calibration and their mean time between failure is rated at 5-10 years.  Uncooled cameras are roughly 1/3 the cost of cooled thermal imagers.

What is the difference between a microbolometer and a ferroelectric array?

Uncooled thermal imagers are available in two different configurations, microbolometers and ferroelectric arrays.  A microbolometer is a “staring” array that uses an iris or shutter flag to re-calibrate the detector every few minutes.  Microbolometers have a very distinct image with crisp edges on the objects in the scene.  The dynamic range of temperature for a microbolometer is somewhat limited when compared to ferroelectric arrays.  This is evident when looking at a scene where a fair percentage of the viewing area is deep space, such as a desert or large body of water.  Since deep space is very cold when compared to planet Earth, this presents a very large dynamic range in temperature.  A microbolometer has to use very advanced histogram equalization software to accommodate this type of scene and even then the user has to be careful to not allow too much deep space or cold in the scene or the hot Earth will wash out.  Microbolometers are also adversely affected by direct or indirect sun light exposure.  If the user points a microbolometer at the sun or a reflection of the sun on a window, irreversible damage can occur to the detector.  Ferroelectric arrays us a chopper mechanism to continuously calibrate the detector.  Each column of pixels is calibrated every 30th of a second.  This allows ferroelectric arrays to encompass a large dynamic temperature range and even look directly at the sun without incurring any damage to the detector.  The image quality is not as sharp as a microbolometer but most users find it difficult to distinguish the two.  Microbolometers are also slightly more sensitive than ferroelectric arrays and allow for greater detection distances.  Ferroelectric arrays are slightly less in cost and out perform microbolometers in desert or large bodies of water scenes where deep space is a factor.  HurleyIR uses either technology and chooses best suited detector for the application.

Why should I be concerned about the number of pixels on a detector?

Like digital cameras and camcorders, the more pixels you have on a detector, the better the image clarity and the farther the device can “see”.  Most thermal imagers today use either a 320X240 or a 640X480 array size.  Larger sizes are expected to be released in 2008.  The larger the array size, the farther a thermal imager can detect energy.

Do thermal imagers see through objects?

Thermal imagers only see the surface of any object and more specifically the energy emitted from any surface.  Thus, thermal imagers do not see through any surface including glass.  Thermal imagers have to use specialized optics such as germanium, ruby and other costly compounds that transmit the infrared wavelength.

What are germanium optics?

Germanium is a crystal compound that is “grown” in a laboratory environment.  It is one of the few compounds that allows infrared wave length transmission.  Germanium is the best in transmitting infrared wavelengths allowing 95% of the wavelength to transmit through the germanium.  Silicon or polymer optics allow infrared transmission but at 75% and 60% respectively.

Can I hide from a thermal imager with camouflage clothing?

Like every other object above absolute 0º, camouflage clothing emits energy and therefore can be detected by a thermal imager.  Nothing can escape detection from a thermal imager.

Why do thermal imagers pick up reflections in water?

Water and other shiny objects such as metals not only are good reflectors of light but good reflectors of energy.  The water reflects energy emitted by the sky such as clouds and even deep space since all objects are above absolute 0º.  When a thermal imager looks a body of water or any other highly reflective object, it often sees the “energy” emitted by surrounding objects on the surface of the water.

What is MIL-STD 810F?

MIL-810-F is recognized both domestically and internationally as the highest standard of environmental integrity available.  When a product has been tested and passed according to MIL-810-F standards, you can be assured that the product will be able to withstand the harshest environmental conditions known.  Extreme heat and cold, blowing sand, salt fog, 3 foot submersion, 3 foot drop on concrete, electromagnetic discharge shielding and explosion proof testing are just some of the standards that must be met to get a MIL-810F rating.  HurleyIR products have been tested and passed MIL-810-F specifications by the US Army.



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