Thermal Scanners & Imagers

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For temperature measuring, I like this little Indoor/Outdoor Thermometer from Radio Shack; part # 63-1023 for about $15. It measures in tenths of a degree, has fairly fast response, seems accurate, and has an EL backlight.

You can also get digital combination weather meters such as this Extech Hygro-Thermometer model with clock which measures both temperature and humidity.



One of the more popular devices out there is the IR thermal scanner. This is a temperature measuring device which works by sending out a thermal beam and measuring the emissivity of a surface. This is to check for or verify unusual cold or hot spots in a room. While it could work in theory for this purpose, there has been some debate about whether a ghost or paranormally induced thermal variation would have enough mass to shift the reading.

Nonetheless, many hunters swear by this device and it is usually one of the second pieces of analysis gear purchased after an EMF meter. Prices range from $40 for the miniature model sold by Radio Shack to over $1000 for high end offerings like the MX Ranger series.

There are a number of features to consider when buying one:

1) Range many of the cheaper ones may only work out to 15 feet or so; too short for any but the smallest rooms.

2) Spot ratio this is a spec which describes how large the sampling spot is in proportion to the measuring distance. The low end models are rated at 6:1, which means that at a distance of 6 feet, the cone of the beam is 1 foot in diameter.  Better ones are at 8:1 or more, while at the very top end it is not unusual to see 60:1 +

3) Temperature resolution this describes the decimal rounding characteristic of the scanner and helps a lot with detecting small changes. Unless otherwise noted, most lower end and even mid range scanners measure to the nearest degree in Fahrenheit, while slightly better ones measure in increments of 0.5 degrees and the best typically go down to 0.1 degrees.

4) Backlighting in low light or no light conditions,(which is common) this is very helpful for monitoring. Will probably drain batteries at a greater rate, though, plus the glare of the screen may interfere with your night vision.

5) Laser pointer I have heard some people say this is unnecessary, but I couldnt disagree more. If you have a thermal anomaly, then you need to pinpoint the area as best you can and the pointer is too convenient to do without. The more sophisticated models have an overlay template which automatically shows the outline of the spot ratio.

6) Display lock with min/max. This can be nice to have, but I dont consider it essential if you have a halfway decent memory or right things down. There are combination digital with bargraph displays on the more expensive meters which help with picking up on transients.

When using an IR scanner, you need to be mindful that certain materials and angles will create false or erroneous readings.

Some things to keep in mind are

Pointing into the sky will create an artificially low reading

Glass and mirrors will typically false

Be aware of cold air vents, hot pipes and the like which can mislead







Thermal image of a Pirate (not a real ghost :) )

Considered to be the ultimate in ghost hunting equipment, I have had the fortune to use several of these devices, including the models below:

Raytheon 400 D 25 mm lens (non-radiometric)

Electrophysics TVS700 35 mm lens (radiometric)

EZ Therm Pro 50mm lens with Compaq PDA display (radiometric)



About Thermal Imaging


Thermal Imaging is the conversion of radiated or reflected heat into real-time pictures or images. A thermal image is an analogue pictorial representation or visualization of temperature differences.

All objects above absolute zero (-273 degrees) emit radiation, some of which is infra-red. Depending on temperature and emissivity, most objects in the world can be thermally imaged.

Infrared Spectrum

Infrared covers four regions of the spectrum; (a) Near infrared, 0.7 -1 micron, this is nearest to the visible wavelength. (b) Short wave, 1.0 - 2.5 microns. Both of these wavelengths regions rely on reflected solar radiation and can only be used in daylight or illuminated conditions. (c) the Medium or short wave thermal infrared, 3 to 5 microns, detects radiation emitted from objects and can be used in total darkness or daylight. This wavelength is often used for high temperatures such as boilers, kilns etc. (d) the Long wave thermal infrared, 8 -14 microns, is most commonly used in industry since the detectors are efficient at environmental temperatures and can also be used for high temperature operations with appropriate filtering.


Thermal Imaging Optics

Most materials are opaque to medium and long wave infrared including glass and water. Optical materials such as germanium and some other exotic materials such as zinc sulphide, zinc selenide, magnesium fluoride and sapphire are used since they are mostly transparent to the thermal wavelength. These materials are very expensive. Some low grade commercial thermal imagers utilize composite materials to lower the costs but there is no compromise where quality is required. Most military specification thermal imagers use coated germanium and optical magnification rather than digital magnification.


Industrial Thermal Imagers

Over the past few years there has been an incredible advancement in thermal imaging technology. Miniature electronics has allowed for cameras to become very much smaller and far more efficient however the optics and detectors are still very expensive.

Industrial applications can be broken down into two basic categories; Ground and Aerial. Although it is not quite this simple, most ground applications can be accommodated using good quality hand-held equipment. Aerial surveys however require high thermal and spatial resolution to provide quality data at long range.

The most common types of thermal imaging equipment used in industry are: Pyro-Electric Vidicon, (PEV), Focal Plane Array (FPA) and the SPRITE (Signal Processing In The Element). The PEV is the lower end of the price scale and image quality but is perfectly acceptable for Electrical Condition Monitoring and close proximity surveys. The FPA is usually of mid range and is used for general survey applications. The SRITE detector is generally used in top grade military equipment. Each type has advantages and disadvantages and more detail can be given on request.


Interpretation of Thermal Images

Aerial or Ground infrared, also known as Thermal Imaging or Thermography, is best suited to give qualitative rather than quantitative data. Infrared non-contact quantitative systems need accurate information of surface emmissivities if radiant energy is to accurately relate to surface temperature.

Thermal images recorded in 8 -14 micron wavelength (Long Wave) have no visible content and no natural colour. Because of the long wavelength, thermal or infrared images cannot compare in spatial resolution to visible photographs that are recorded in 0.4 -0.8 micron band. Thermal resolution and spatial resolution are inter-dependant to produce good quality thermal images, therefore if a house roof is close to or the same temperature as the nearby road, for example, the image will appear dull grey with little detail. Temperature contrast will produce picture or image contrast and high detail.

Thermal imagers detect and record Infra-red radiation emitted from the surface of any subject being viewed. The imager does not have the ability to see below the surface. However, the radiation from the surface is often influenced by sub-surface detail, which effects the thermal characteristics of adjoining material(s).

When looking at a large area, the emissivity of various surfaces must be considered. Most materials found on the surface of buildings will have a relatively high emissivity but there will still be noticeable differences in the perceived image due to a change in surface material. This can be overcome by a detailed knowledge of the building under investigation. Some metals and glass can reflect infra-red radiation and apparent 'hot spots' can be a reflection from a hot object nearby.

Infra-red aerial surveys provide a 'global' visualization of heat radiation from building surfaces. It is useful data for determining areas of concern or for determining work priority. We can also provide detailed ground level thermal imaging surveys in support of aerial data.

Infra-red surveys of heated buildings are always conducted during the evenings of the Winter/Autumn months of the year.

Aerial thermal Imaging for surveying buildings for heat loss and moisture operate in 8-14 micron wavelength and detect heat only, visible light is not detected at all. Heat energy from daytime sunshine can be absorbed in brickwork and therefore a survey is conducted well after sunset to ensure that all effects of solar energy have dissipated. 

Infra-red - just like visible light - absorbs, reflects and re-radiates from materials in amounts depending upon their colour and structure. Brown building bricks for example absorb and retain heat energy more readily than lighter colored building materials, this must be considered when analyzing data since they may effectively appear at different temperatures simply due to their emissivity. Water bodies such as rivers or lakes retain heat and are slow to change with ambient temperature changes, whereas ground surface temperatures can change rapidly. This is why water often appears warmer than its surroundings.

A thermal Imager detects and displays surface temperatures only. The surface temperature under normal conditions is the result of heat energy conduction through the walls from a heated internal room. Moisture is an excellent conductor of heat and when insulation is damp it can become a conductor rather than an insulator. 

When analyzing thermal data, monochrome images are normally preferred because of the wide range of grey tones of temperature that can be differentiated by computer. There are of course no natural colors in the long wave infra-red wavelength so we apply a palette of colors to the grey tones. Colour images are very much easier for the naked eye to interpret so both color and monochrome are supplied.

To assist in analyzing your aerial data a temperature palette is provided for assessing temperature differences.


Haunted Dublin Castle


A measure of the ability of a surface to radiate energy as measured by the ratio of the radiant flux per unit area to that radiated by a black body at the same temperature. 

Example:- Black body = 1.00
Red Rough House Brick = 0.93
Polished Aluminum = 0.095



Emissivity is a measure of the thermal emittance of a surface.  It is defined as the fraction of energy being emitted relative to that emitted by a thermally black surface (a black body).   A black body is a material that is a perfect emitter of heat energy in that it emits all energy it absorbs and has an emissivity value of 1.  In contrast a material with an emissivity value of 0 would be considered a perfect thermal mirror and imaging this material would result in readings of reflected energy only and not the actual material.  For example, if an object had the potential to emit 100 units of energy but only emits 90 units in the real world.  That object would have an emissivity value of 0.90.  In the real world there are no perfect "black bodies" and very few perfect infrared mirrors so most objects have an emissivity between 0 and 1.

 Emissivity is a variable that makes it very difficult to obtain exact temperature readings with an infrared camera or spot radiometer.  This is due to the fact that it is highly impractical to measure the emissivity of every object in your field of view.  For example, if you are scanning an electrical panel in a predictive maintenance application you will be imaging wires, fuses, nuts, bolts, and other materials all of which will have a different emissivity value.  So how do we obtain accurate reliable information? 

As stated before it is hard to determine the emissivity of all objects in your field of view.   It is also difficult to determine the emissivity of a single known material.   This is because emissivity is a measure of the "surface" emittance of an object.  The surface of objects (especially metals) changes with the passing of time.   For example, if you look at the table below you will see that corroded copper (E 0.78) has a significantly different emissivity value than shiny copper (E0.02).  This difference introduces a judgment call on the part of the thermographer.  How do you determine how corroded or shiny a piece of copper is? 

The answer is you can come close but you cannot be exact.  Additionally, the numbers in the emissivity table are approximates or averages, in the real world values may be skewed.  So how do we manage emissivity.  It is possible to determine actual emissivity values for a material but it is not practical in the real world.  The process requires a spectrometer (expensive and usually not available) or dismantling the object and testing each piece.  Even if you determine an accurate E value, the next time you scan the item that value will have changed rendering your old value useless.  In most infrared applications exact temperature measurement is not necessary. 

For example, if a circuit has a fault limit of 150 F and your instrument measures 100 F and the E value skews the temperature reading by 5F  you are left with a +- 5F variance which in this case is negligible.  Additionally, most thermal infrared applications rely on temperature difference (Delta T ) rather than exact temperature readings.  To use our previous example of the circuit we measured, there would most likely be more than one circuit next to each other.  If you use the same E value for both circuits they will both be skewed the same amount.  If the one circuit was reading 100F (which we will assume is normal operating temperature) and the adjacent circuit reads 150F we are left with a Delta T of 50F which would indicate a problem and as you can see negates the emissivity problem.  E values become even less of a problem when trending an area over time.  If the same circuit with the reading of 100F has a reading of 110F the next time you scan it and a reading of 115F the next time, with the same emissivity setting, we know a problem is developing regardless of the error introduced by emissivity.  

Dealing with emissivity is not as hard as it would seem.  The important things to remember are that exact temperature measurements are difficult to obtain (do not promise this to your clients unless you are sure you can back it up), temperature difference (Delta T) is more important than exact readings in most applications, and that trending an object can reveal problems regardless of E value error.  In the real world you pick an emissivity value that approximates the scene you are imaging and then you record it and maintain that same setting every time you scan that object.



Seeing Heat Energy

The human eye is designed to see visible light and colors as we know them but below red or infra-red is beyond our capabilities. Infra-red light is not visible but can be sensed and felt as warmth. An infra-red camera or Thermal Imager detects heat energy and converts it to an electrical signal which is then processed into an analogue representation of the subject. Since there are no colors in the infra-red spectrum, 
(8-14 microns) color palettes are assigned to the grey tones to represent temperature bands. 

Atoms and molecules are affected by magnetic and electrical components of light.
Different materials absorb and reflect thermal infra-red at different wavelengths depending on the composition of each material. A heat 'signature' can therefore be assigned to each mineral. Visible light is also absorbed and reflected off materials at different wavelengths and we see these as colors.



The Electromagnetic Spectrum

The Infrared region is part of the Electromagnetic Spectrum that is dividing up all types of electromagnetic radiation.  This radiation is divided up rather arbitrarily into a number of regions based on their wavelengths:

Gamma < 10 nanometers

Ultraviolet radiation

Visible light 0.4 to 0.7 micrometers

Infrared Radiation


Radio waves 


The Infrared Spectral Range

Infrared is a specific region of the electromagnetic spectrum that is just beyond the light region.  The Infrared region spans from 1 to 1000 microns.  


Near Infrared 0.75 to 2 micrometers


Middle Infrared 2 to 6 micrometers


Far Infrared 6 to 14 micrometers


Extreme Infrared 14 to 1000 micrometers


Infrared Thermography 3 to 5 & 7 to 14 microns

The regions that Infrared Thermography primarily deals with is the Shortwave region from 3 to 5 microns and the Longwave Region from 7 to 14 microns.  The cameras that are used in Infrared Thermography simply see the heat that is emitted from the surface of the object that it is viewing.  These types of cameras are used for applications like routine Preventive / Predictive maintenance inspections on electro-mechanical equipment. Where the thermal image of the equipment, as well as temperature measurements, can forewarn a pending failure.  The cameras that are used in Infrared Thermography do not see through objects or into buildings through the walls. Infrared Thermograph is:


Non Intrusive


Non Invasive




Infrared Photography 0.7 to 0.9 micrometers 

Infrared photography involves the production of photographs by means of near-infrared radiation. This radiation that lies in a range roughly between 700 and 900 nanometers can be recorded on specially sensitized photographic emulsions. Infrared radiation actually comprises a much greater part of the electromagnetic spectrum, most of which cannot be recorded directly by photographic means. Elaborate electronic equipment is required to record heat waves as in Infrared Thermography.

Near-infrared radiation has the ability to penetrate aerial haze, which makes it possible for you to photograph distant terrain, a valuable factor in aerial photography. Even more important is the way in which foliage is recorded on infrared-sensitive emulsions. The internal structure of leaves reflect infrared strongly, so that they appear lighter in tone in the photograph than they do when viewed directly. The usefulness of infrared photography lies in the unique tonal differentiation that it produces. Conifers, for example, appear darker than the leaves on deciduous trees; diseased fruit and vegetable crops or those suffering climatic or nutritional stress can be detected before trouble becomes apparent visually. These features of infrared photography become especially valuable in pictures taken from the air.


Night Vision / Light Intensifiers 0.45 to 0.95 micrometers

In Night Vision systems Gen I/II, in low light situations, the foremost lens collects low levels of light that are reflected off of objects that cannot be seen with the human eye and focuses it on a image intensifier tube. Inside the image intensifier tube a photo cathode absorbs this low level of light energy and converts it into electrons. These electrons are then passed through a microchannel plate that multiplies them thousands of times and drawn toward a phosphor screen. When this highly intensified electron image strikes the phosphor screen, it causes the screen to emit a amplifies image that can be seen with the human eye. Since the phosphor screen displays the image in exactly the same pattern and degrees of intensity as the light that is collected by the objective lens, the bright nighttime image you see in the eyepiece corresponds precisely to the outside scene you are viewing.

This type of systems work great for seeing night time scenes in low light conditions but do not provide a thermal image that corresponds to the amount of heat (thermal radiation) that is emitted from the object. Because of this this type of  equipment is not used in Infrared Thermography.


Society for Paranormal Investigation using a Thermal Imager for Ghost Hunting


Infrared Viewing Training Tips: Top 10 Techniques


  1. 1) Is the thermogram qualitative or quantitative?

Consider whether the thermogram is going to use to "illustrate" a condition or used to "Measure" a condition.  This will greatly effect the type of thermogram that you are going to store.  For example you may need to get temperature measurements from a thermogram but you may need to illustrate the condition to others, and the thermogram that you would use to get temperature measurements with most likely would not be the best to adequately illustrate the condition.  Understand what the end objective of storing a thermogram is will greatly effect the way you work.


  1. 2) Get closer to your target

As a general rule, the closer you get to your target, the better your thermograms and temperature measurements will be. Getting close helps to shows the target clearly by maximizing the cameras detectors IFOV across the target providing better resolution.

Think about showing just enough of the scene to make the thermogram clear and provide enough information so that someone can understand what the target is in the FOV. Be sure to check your camera manual to learn the closest distance at which your camera takes sharp thermograms.


  1. 3) Know your Measurement Field of View

If you are working with a infrared camera that can measure temperature then you must learn what the working distance is for accurate temperature measurements of different size targets.  This is a key point in being able to accurately measure a object and is the most overlooked parameter in taking good thermograms for temperature measurement.


  1. 4) Keep the background simple

When working outdoors doing utility inspections most of the equipment is close to ambient temperatures, but the sky is very cold.  By silhouetting the target against the sky you focuses attention on the target that will increases the contrast between the background and the target in your thermograms.  you may need to move a little to avoid obstructions in the background but the results will be worth it in your thermograms. 


  1. 5) Place the target off center

There is nothing wrong with placing the target in the center of your viewfinder. However, placing the target off-center can make the composition more dynamic and interesting to the eye.


  1. 6) Consider what the foreground in your thermogram is doing

When taking thermograms of large areas, try including objects in the foreground. Elements in the foreground add a sense of distance, depth and dimension.


  1. 7) Consider the effects of Solar Reflection and Gain

When working out side consider what the effects of solar reflection and solar gain will do to your thermograms and temperature measurements.  It may be necessary with older types of infrared cameras to work at night to eliminate the solar reflections that show up as faults hot spots.


  1. 8) Hold your camera steady

Sometimes good thermograms are missed by overlooking the basics. Holding the camera steady is vital for sharp, clear pictures. Many older infrared cameras have very slow frame rates so it is very important to hold the camera still when storing a thermogram. When you push the store button, press it gently rather than jabbing it. Even slight camera movement can rob your pictures of sharpness. Use a brace to steady your arm or use a tripod, if necessary.


  1. 9) Get your target in focus

You can improve the thermogram in many ways after you store the image but you will never be able to get in focus if it was stored out of focus in the field.  Take your time to get it right the first time and you will save yourself a trip back to the field.


  1. 10) Choose the right range

You must understand what temperatures that you are going to be imaging so that you can set up your camera to view the right temperature range correctly.  This will effect not only the quality of your thermogram but also your temperature measurement accuracy as well.


 Information posted courtesy of Mayfield Thermography at  located here in Dallas, TX.

Infrared Thermal IR Scanning Thermography in Dallas TX

horizontal rule


"As with sounds, so with colors. At each end of the solar spectrum the chemist can detect the presence of what are known as 'actinic' rays. They represent colors integral colors in the composition of light which we are unable to discern. The human eye is an imperfect instrument; its range is but a few octaves of the real 'chromatic scale.'

I am not mad; there are colors that we cannot see.

"And, God help me! The Damned Thing is of such a color!"

from The Damned Thing

By Ambrose Bierce