How Themal Imaging Works:
Traditional, light intensifying, night vision devices create an image from the light that is reflected of objects. This means that the quality of an image produced by these devices is dependant on the constant presence of ambient light (such as starlight or moonlight). This means that this technology will not work in total darkness.

Thermal imaging devices on the other hand create an image from the Thermal Infrared Spectrum. This is light that is emitted by an object and not reflected. Movement of atomic particles in all objects creates heat (in form of IR light) and it is this heat that is used by thermal devices to create an image. This means that the thermal imaging devices can be used in total darkness and can allow users to see through smoke, dust, light fog, foliage and camouflage.
 
How it Works:
A special lens focuses the infrared light emitted by all of the objects in the view.

The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. This information is obtained from several thousand points in the field of view of the detector array and the whole process only takes about one-thirteenth of a second.

The thermogram created by the detector elements is translated into electric impulses.

The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.

The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.
 
 
Types of Thermal Imaging Devices
Most thermal-imaging devices scan at a rate of 30 times per second. They can sense temperatures ranging from -20 degrees Celsius to 2,000 degrees Celsius, and can normally detect changes in temperature of about 0.2 degrees Celsius.

There are two common types of thermal-imaging devices:

Un-cooled - This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the battery built right in.
 
Cryogenically cooled - More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 0 degrees Celsius. The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can "see" a difference as small as 0.1 degrees Celsius from more than 300m away, which is enough to tell if a person is holding a gun at that distance!

Unlike traditional night-vision equipment which uses image-enhancement technology, thermal imaging is great for detecting people or working in near-absolute darkness with little or no ambient lighting (i.e. stars, moonlight, etc.)