How Do Thermal Imagers Work?
Thermal Imaging
Thermal imaging equipment has important applications in photography, hunting, science, security and even the military. Night vision technology is currently the most common form of thermal imaging, a fact that should come as a surprise to no one. Unlike many other species of animals, humans are virtually blind when in the dark, often requiring an external light source in order to perceive their surroundings.
Thermal imaging technology eliminates this dependency by using infrared radiation from heat to produce visible images, even in the complete absence of normal light. Though night vision alone is a wonderful technology, the applications of thermal imaging are numerous. In order to truly understand any of the applications of this sophisticated technology, however, we need to know a little about electromagnetic radiation first.
Electromagnetic Radiation and Infrared Light
Radio waves, visible light, X-rays and infrared waves are all forms of electromagnetic radiation. Though not completely understood, this force appears to have been present almost everywhere in the universe since the beginning of time. The light of the visible spectrum, what we typically see, is just a small fragment of its vast range of wavelengths.
The "black body radiation law" from physics states that when a body emits heat, it also emits thermal radiation. Unless the body in question is extremely hot, the thermal radiation will likely fall into the infrared band of the spectrum. Infrared typically has a wavelength of over 900 nanometers, whereas the human eye can only pick up waves in the 400 to 700 nanometer range. Under normal circumstances, we are completely unaware of its existence, but with thermal imaging we can put it to good use.
Night Vision and Thermography
Night vision uses ambient heat and the infrared it emits to produce visible images. Heat is always present, even at night, covering the entire surface of the earth with varying levels of infrared radiation. By absorbing this ambient infrared, converting it into an electrical signal and amplifying it into the visible range, a night vision device can effectively translate infrared into visible light and reproduce the image digitally for the viewer.
Above, we discussed how heat causes a body to emit infrared radiation. The magnitude with which this occurs depends on what material the body is composed of. Some materials readily emit infrared, whereas others barely emit any, even when incredibly hot. In terms of night vision, this simply means that objects composed of certain types of matter will be more visible than others. In the field of thermography, however, it means much more.
Thermography is the method of measuring an object's temperature with an infrared camera. If the emissivity of the object is known, the intensity of the thermal image can be used to calculate the object's surface temperature. Using this technique, temperature measurements can be taken from a distance, faults can be found in metal parts and machinery, and medical personnel can view a patient internally and non-invasively.
Tags: infrared radiation, electromagnetic radiation, emit infrared, Imagers Work, into visible, night vision, Night vision
