Thermal vision devices and riflescopes
What is a Thermal vision?
Every object having a temperature above the absolute zero (- 273.2°C) emits electromagnetic waves in infrared range.
According to the laws of physics, intensity of thermal emission is proportional to the fourth power of temperature of the heated object.
Consequently, detection ability of heated objects’emission by receivers sensitive in the infrared range depends mainly on temperature of the object and its surrounding background.
It does not depend practically on the illumination level in the visible range.
Infrared emission occupies an extensive part of the spectrum, which is commonly divided into several ranges:
Fig. 4. Spectral ranges of observation devices and atmospheric transparency windows vs. emission wavelength.
NV –Night vision device range (from 0.4 to 1 microns);
SWIR – Short wave Infrared range (from 0,76 to 3 microns);
MWIR – Mid wave Infrared range (from 3 to 6 microns);
LWIR – Long wave Infrared range (from 8 to 14 microns).
A commonly accepted division of infrared emission into ranges is connected with both sensitivity ranges of existing receivers and atmospheric transparency windows.
A night vision device works in visible and close infrared ranges (wavelengths from 0.4 to 1.0 microns) thanks to detection of natural and artifi cial light refl ected from observed objects.
A modern compact thermal vision device works in the range from 8 to 14 microns that corresponds to one of several atmospheric transparency windows.
The action principle of thermal vision devices is based on the ability of certain materials to register object images formed by infrared emissions and transform them into electrical signals.
Received electrical signals that are determined by the thermal scene of observed terrain are transferred onto built-in micro display after amplifi cation and software processing.
The display transforms these signals into a picture of observed objects that is visible by human eye.