EW Academy · Contents · Chapter 6 · Nederlandse versie
Chapter 6: Infrared
Thermal radiation as a sensor: the division of the IR spectrum, active and passive infrared systems, and the physical limitations of IR.
6.1Introduction
Infrared (IR) is the part of the EMS between radio waves and visible light: from 300 GHz to ~394 THz, or wavelengths from 1 mm to 760 nm. Invisible to the eye, but felt as heat — and a goldmine for sensors.
Read §6.1 →6.2Division of the infrared spectrum
Anything warm emits infrared. The hotter something is, the shorter the wavelength at which that radiation is strongest. A hot exhaust (600–1000 K) radiates mainly at 3–5 µm (MWIR), a person or vehicle (around 300 K) at around 10 µm (LWIR).
Read §6.2 →6.3Active and passive infrared
As with radar, we distinguish active and passive systems — but with IR, passive is the norm:
Read §6.3 →6.4Disadvantages of infrared
Infrared sees differences in heat; it does not see through everything. Fog, rain and clouds absorb the radiation, and when everything is equally warm, the contrast disappears.
Read §6.4 →6.6IR seekers up close
The best-known passive IR application is the seeker head of a heat-seeking missile — from shoulder-launched MANPADS to modern air-to-air missiles. The seeker has to do one thing very well: find the target's heat, hold on to it and turn it…
Read §6.6 →