Infrared radiation was discovered in the year 1800 by Sir William Herschel when he observed that some type of “invisible” radiation appeared to be emitted by a prism illuminated by sunlight. This energy could heat up a mercury bulb thermometer in the far reaches of the visible red region, thus the term in-far-red. Infrared radiation includes electromagnetic waves (or photons) from 0.75 m to 1000 m, the spectral region between visible light and sub-millimeter microwaves. Infrared radiation is emitted by all substances above absolute zero.
When detecting the infrared radiation given off by an object, it is possible to determine its average radiation temperature. By measuring the infrared radiation emitted by the local sky above a radiometer, we are, in effect, measuring the radiation temperature of the sky. Depending on the discipline, this method of indirect temperature measurement is referred to as non-contact thermometry or pyrometry.
All objects above absolute zero emit infrared energy. The hotter an object is, the more active its molecules are, and the more infrared energy it emits. An infrared thermometer houses optics that collect the radiant infrared energy from the object and focus it onto a detector. The detector converts the energy into an electrical signal, which is amplified and displayed.
Also be aware of emissivity. Emissivity is the ability of an object to emit or absorb energy. Perfect emitters have an emissivity of 1, emitting 100% of incident energy. An object with an emissivity of 0.8 will absorb 80% and reflect 20% of the incident energy. Emissivity may vary with temperature and spectral response (wavelength). Infrared thermometers will have difficulty taking accurate temperature measurements of shiny metal surfaces unless they can adjust for emissivity.
How can the emissivity of an object be determined?
1. First, measure the surface temperature of the object to be measured with a surface-type thermocouple probe. Measure the same surface with an IR thermometer, adjusting emissivity on the thermometer until the temperature readings on both the thermocouple and IR meters agree.
2. For temperatures up to approximately 500 deg F (260 deg C), place a piece of regular masking tape on the object to be measured. Allow the tape to reach thermal equilibrium with the object. Using an IR thermometer with the emissivity set at 0.95, measure and note the temperature of the masking tape. Then, measure the surface temperature of the object. Adjust the emissivity until the temperature of the object is the same as that of the tape.
How to use it in our Research: Emissivity is a large concern of many people in this field as some objects absorb thermal radiation and others reflect it. For our research we are primarily interested in anomalous thermal deviations, not the exact temperature of an object. Therefore if an object we are targeting absorbs or deflects thermal radiation, it is irrelevant. Our objective is to determine if there is in fact an anomalous thermal deviation within a location. By doing this, we are focusing our attention to any significant thermal deviations between the scanner and the target, regardless if the target has high or low emissive rating. If the surface of a target is registering at 74 degrees and within a period of 3 seconds registers at 52 degrees, no amount of emissivity can explain such a deviation of thermal radiation. This is in fact an anomalous thermal deviation and exactly what we are looking for.
The Non-contact Thermal Scanner has become an invaluable tool in the research of life after death. Like most of the equipment we use in our research, it was not designed for what we do with it. Many people use this piece of equipment improperly. This thermal scanner is to be used at a stationary location and should be monitored constantly. The measuring diameter of this device will “cone” outwards, much like a flashlight, and detect photons that enter this “cone.” If you are stationary in a location you can cover a large area with one scanner. A lot of times these anomalies will move very fast through the scanner’s measuring diameter. This is why it needs to be monitored constantly, and stay stationary, as some of the thermal deviations will last only a few short seconds.