PART A: BASIC INFRARED THEORY
1. Most people associate IR with temperature rather than electromagnetic energy. This is
not entirely wrong. A direct relationship exists between heat (temperature) and IR. For this
reason, some understanding of IR is needed.
2. IR radiation. Reconnaissance and surveillance (R&S) systems are based on the ability of
the sensors to detect radiation from the terrain below. An increase in the temperature of a
body will cause an increase in the amount of IR generated.
3. Electromagnetic energy. IR is electromagnetic energy. All objects having a temperature
above absolute zero (above minus 460 Fahrenheit) emit IR. Absolute zero is a point where
all molecular activity ceases (Figure 1-1).
Figure 1-1. Temperature Scale Equivalents.
4. Molecular activity. Atoms and molecules are in a constant state of activity. This activity
causes friction as the atoms and molecules bump into each other. This friction raises the
temperature of a body of atoms or molecules. External heat also increases the molecular
activity and consequently the friction. The result of this phenomenon is that every body of
atoms or molecules emits heat. The amount of heat emitted also determines the amount of IR
energy in the electromagnetic spectrum (Figure 1-2).
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