Tuesday, February 14, 2012

The IR Thermometer Pitfall

This article is from TAPS.Com

Article by: David Betz

The measurement of temperature is an important component of any standard investigation and the proper collection of this type of environmental evidence can assist in validating the overall phenomenon. Paranormal research is not an exact science and relies heavily on circumstantial evidence. "I heard a noise" or "I feel cold here" are some basic examples of claims normally linked to something paranormal. Though attention to the feelings that one has should never be overlooked, it would seem logical that both of these claims, if happening outside the head of the witness, are fully able to be verified via the accepted sciences and the tools used to measure their deviations. Obviously, the more of this direct evidence that is collected, in support of the overall evidence, the more credible the claim will be.

Given the importance most reputable investigation organizations apply to temperature measurement, the IR thermometer has made the list of recommended tools for every investigator's toolbox. The simplicity of use and the accessibility is, no doubt, the primary goal driving these recommendations. However, I do see an inherent problem in the recognized use of this instrument in the types of measurements I have seen being taken from it.

Surface Temperature versus Air Temperature

IR thermometers are a wonderful invention and very accurate when used for what they are intended. These devices were designed to measure the surface temperature of an object that cannot, for whatever reason, be touched with a temperature probe. Whether you are trying to measure the temperature of molten steel or the body temperature via the ear canal, there is an IR thermometer to fit your application; however, these thermometers are grossly inadequate for measuring ambient air temperature. It is in this difference, surface temperature versus ambient air temperature, where I feel the error is being made.

Surface temperature, in essence, is the temperature as measured at the "skin" of a specific object. It isn't necessarily the temperature of the object itself, but rather the temperature just at the outside of the object, being that surface temperature is affected by A) the temperature of the surrounding air (ambient air) and B) the temperature of the core that the object and C) the surface temperatures of any other objects that may be touching the object (i.e. a temperature probe). Each of these systems push and pull the temperature of the object's surface until a thermodynamic equilibrium is reached between all the relevant thermal systems. The time in which equilibrium is met depends greatly on the temperatures differentials between the systems, the materials involved as well as the density of the object that is being measured. Granted, the surface temperature is a relatively accurate measurement for the overall temperature of the object, but this wouldn't be true if the object was in the state of being heated or cooled from within. Barring that, and for most cases that a paranormal investigator would run across, this wouldn't much matter. However, to understand this dynamic can assist when temperature readings are unusual and a rational reason for the unique data point is being sought.

Ambient air temperature is basically the temperature of the surrounding air. Most of us should be aware of the ambient air temperature in our daily lives. It is given to us during weather forecasts each and everyday. Most of us have a certain air temperature for which we are most comfortable. And if you have ever lived with someone that enjoys a different air temperature than you, it can be the source of a good deal of household tension to say the least.

The point I am trying to drive home is this, surface temperature and ambient air temperature are two completely different measurements and do require a different tool to properly and accurately measure.

The Pitfall

Simply pointing your IR thermometer in some general direction will give a reading, but that reading would never stand up to any scrutiny of the evidence and has the potential of all collected evidence to be called into question. After all, if this measurement was wrong, how can the rest of the evidence be trusted? Why let the good evidence get holes unnecessarily shot through it, because of an improperly collected set of evidence that could have otherwise supported the rest of the evidence?

Through my own experiences on investigations and my reading of many investigation reports, it is my opinion that many investigators are mistaking the readings provided by their IR thermometers. When an area feels cold, a quick reading is taken and offered up as a validation for what they are experiencing. I have also seen good investigators discounting their own logic by refusing to question what their equipment is telling them. If the meter reads 35 degrees, it must be 35 degrees regardless of what their senses are telling them. Either way, this type of data collection is wasteful and misleading, resulting in a false positive that can waste hours of valuable investigation time and provide for some red faces when the data is scrutinized.

What does an IR thermometer measure?

An IR thermometer was designed specifically to measure the surface temperature of an object. If the intension is to measure the temperature of a particular object rather than the ambient air temperature, then this is definitely the tool that would need to be used. I certainly wouldn't hesitate to use this tool on an object that someone claims to have an energy attached to it. The beauty of the tool is that you aren't touching it; therefore you are not risking the transfer of heat between the object and a temperature probe nor your hands, which could be a significant factor when dealing with phenomenon that lasts seconds in duration. This tool is perfect for this application as this is the intended design of this type of thermometer.

In my research of this device, I have heard the incorrect claim that these devices, much like a camera, have a focal point and if you simply stand far enough away from any object, you are measuring the heat at that point in space. In a round about way, the claimants are stating that an IR thermometer is essentially measuring the temperature of the air out in front of the sensor. This is simply not true and, in fact, this action may give bizarre readings making the investigator wonder if something is there or not.

Heat is transferred in three distinct ways - conduction, convection, and radiation. Conduction involves the transfer of heat through solids. Convection involves the transfer of heat through liquids or gases. Radiation involves the transfer of heat through empty space, or a vacuum. These are all simple statements, but what really should understood is that IR thermometers deal with only one of these measurable properties - radiation. Electromagnetic energy, such as light or radio waves, are familiar examples of radiation. Heat is also transferred via radiation just as the sun warms the Earth through radiated energy traveling through 93 million miles of empty space. The amount of heat that is being radiated is directly proportional to the intensity (amount of light energy) the object emits. IR thermometers simply measure the intensity of the infrared radiation at a specific infrared wavelength, as defined by the specific IR thermometer's specifications.

To directly address the belief that an IR thermometer can be used to measure air temperature, it should be understood that the absorption coefficient (how much heat an object can store) of air is very small in the infrared wavelength ranges. This means that you will pickup a very small amount of the infrared from the surrounding air, but the radiance from the objects in front of the sensor are more likely to sum into your reading. Therefore, you are effectively measuring the small amount of radiance from the air between the sensor and any stray radiance from other objects that the sensor happens to be pointing at, regardless of how far away it is. The properties of infrared light is the same as visible light, particularly that it will travel through clear air without much loss in intensity.

This isn't to say that the distance between the sensor and the object isn't important; however, the importance isn't in "what" you are measuring, but how accurate the measurement is. Most IR thermometer manufactures recommend a 1.5 to 2 target size to distance ratio. What this means is that you multiply the size of the object by 1.5 to 2 to come up with the distance that the sensors should be away from the object in order to give the most accurate measurement.

What is the alternative?

I believe the starting point in a paranormal investigation, when considering temperature, is the measurement of the ambient air temperature. From what I have read in past investigation reports and from what I could glean from the descriptions in the various equipment recommendations, this seems to be what most investigators are looking for in a general temperature measurement tool for their investigation toolbox.

My recommendation is to use a thermocouple based temperature measurement device. Most thermocouple devices have a measuring unit of less than 3cm which would be more capable of accurately and decisively measuring rapid changes of ambient air temperature. It is feasible that a moving cold spot could be followed and/or mapped with such a tool that could react quickly to changes in air temperature. It is my opinion that these types of thermometers are far better suited for the purposes of the average paranormal investigator.

In making the selection for my recommendation, I was looking for something accurate, easy to use and comparable in price to the average recommended IR thermometer. I have chosen the Omega HH501AT digital thermometer as my recommendation for this application. This device comes with a "T" type thermocouple, which has faster response times in the temperature ranges that a paranormal investigator is concerned with. Overall, this was the best all around meter that I could find that works right out of the box.

What should I do with my IR Thermometer then?

I am not saying that you should toss your IR thermometer out the window. It does have applications in a paranormal investigation, but it should compliment your temperature measurement tools rather than be the focus. An IR thermometer, used in conjunction with a thermocouple device, could be used to provide more compelling data. For example, "the ambient air temperature was 85 degrees, as measured with our thermocouple thermometer, but the object stayed at a consistent 74 degrees, as measured with our IR thermometer." That is fairly significant and compelling data that would be difficult, at best, to discount provided all the data was collected properly.

What can affect the IR thermometer measurements?

There are a few things that can throw off an IR thermometer reading and should be in the minds of the investigator as they are collecting temperature data with this device. Just as you would look for reflective areas when taking stills and ensuring that a fresh tape is used in your audio recorders, you would need to be mindful of these following conditions while you are taking measurements with your IR thermometer.

The emission from an object may be influenced by absorption and scattering in the optical path. Given that the only thing the IR Thermometer measures is emission of radiated energy, this means a lot. Water vapor, smoke, dust and various gases, such as CO2, can drastically affect these measurements. Think about it this way, if the object is being obstructed by a slightly opaque material, the radiated energy is obviously lessened. Remember that infrared light is subject to the same physics as visible light.
If there is excessive dust, dirt, fingerprints, etc collecting on the sensor's glass plate an accurate temperature measurement would be next tom impossible. As with any piece of equipment, your IR Thermometer will need to have some basic general maintenance.
Polished metal and mirrored surfaces are impossible to get an accurate measurement from without a modification to your IR Thermometer. What actually ends up happening is that you measure the surface temperature of the glass plate that protects the sensor housing of your IR Thermometer. Simply said, you are measuring the temperature of your IR Thermometer, because you are essentially looking at your temperature probe in a mirror. There are special glass coverings that can be used to do this, but don't look for it in a low end IR Thermometer.
Depending on the manufacturer, EMF could play havoc on your IR Thermometer. This is obviously true with any electronic device, but nonetheless worth mentioning.

Needless to say, care must be taken with taking temperature measurements, with this device, to ensure the best overall accuracy in your temperature measurements of an object and to keep you from chasing your tail from a false positive.


I believe the first rule of any investigation is to seek the truth, regardless of what that truth may be. As much as any paranormal investigator, I would certainly like to believe that I am surrounded by the unknown and the unknown is interacting with my physicalness when I am on an investigation. But I refuse to excite myself and my colleagues with data that I know to be collected improperly, because I wasn't using the right tool for the job. Such shortcomings are so easy to overcome if a little bit of rationalization, knowledge and experience is applied to the equation. To me, it makes the real data, collected in a rational, professional manner, which supports the feelings and sensations we all have had or heard about, that really excites me and makes me want to continue.

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